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Over the past 30 years, the Arctic Dipole Anomaly (DA) has repeatedly led to record lows in summer sea ice extent, with cloud radiative effects (CRE) playing a crucial regulatory role. Here, we reveal the CRE variations between positive and negative DA events and elucidate the slowing impacts of CRE on sea ice thickness (SIT) changes. The DA triggers robust meridional winds and transpolar drift, markedly reducing SIT in the Beaufort Sea (BeS), Chukchi Sea (CS), and East Siberian Sea (ESS), while increasing it in the Greenland Sea (GS). CRE significantly slow SIT changes, contributing +14.4, +4.4, +16.4, and −26.7 cm to changes from June to August, against total changes of −55.9, −29.4, −39.8, and +42.8 cm in September over BeS, CS, ESS, and GS, respectively. This study underscores the key impacts of CRE on sea ice variation, emphasizing their significance in the polar climate system. Plain Language Summary: The Arctic Dipole Anomaly is one of the principal atmospheric circulation patterns in the Arctic region, significantly influencing the spatial distribution of sea ice through induced changes in polar wind directions. These wind changes also affect the fraction of Arctic clouds and, by modifying cloud‐surface radiative forcing, alter the surface energy balance. Utilizing 20 years of multi‐source observation data along with reanalysis meteorology, we observed that during the summer, a positive Arctic Dipole Anomaly significantly decreases the thickness of sea ice in the Pacific sector and increases it in the Atlantic sector. During this period, variations in cloud‐surface radiative forcing substantially slow the extent of sea ice thickness reduction/increase. In other words, without considering the impact of cloud radiative forcing, the changes in sea ice thickness would be more severe. Key Points: There is a significant reduction in both the sea ice concentration and thickness across the Pacific sector of the Arctic with Arctic Dipole Anomaly phases in summerThe Arctic Dipole Anomaly induces alterations in the wind and temperature fields, which subsequently influence the spatial distribution of Arctic cloudsVariations in clouds and surface albedo alter the surface energy balance and slow the sea ice changes caused by the Dipole Anomaly [ABSTRACT FROM AUTHOR]

Aerosol‐cloud‐precipitation interactions are a leading source of uncertainty in estimating climate sensitivity. Remote marine boundary layers where accumulation mode (∼100–400 nm diameter) aerosol concentrations are relatively low are very susceptible to aerosol changes. These regions also experience heightened Aitken mode aerosol (∼10–100 nm) concentrations associated with ocean biology. Aitken aerosols may significantly influence cloud properties and evolution by replenishing cloud condensation nuclei and droplet number lost through precipitation (i.e., Aitken buffering). We use a large‐eddy simulation with an Aitken‐mode enabled microphysics scheme to examine the role of Aitken buffering in a mid‐latitude decoupled boundary layer cloud regime observed on 15 July 2017 during the Aerosol and Cloud Experiments in the Eastern North Atlantic flight campaign: cumulus rising into stratocumulus under elevated Aitken concentrations (∼100–200 mg−1). In situ measurements are used to constrain and evaluate this case study. Our simulation accurately captures observed aerosol‐cloud‐precipitation interactions and reveals time‐evolving processes driving regime development and evolution. Aitken activation into the accumulation mode in the cumulus layer provides a reservoir for turbulence and convection to carry accumulation aerosols into the drizzling stratocumulus layer above. Further Aitken activation occurs aloft in the stratocumulus layer. Together, these activation events buffer this cloud regime against precipitation removal, reducing cloud break‐up and associated increases in heterogeneity. We examine cloud evolution sensitivity to initial aerosol conditions. With halved accumulation number, Aitken aerosols restore accumulation concentrations, maintain droplet number similar to original values, and prevent cloud break‐up. Without Aitken aerosols, precipitation‐driven cloud break‐up occurs rapidly. In this regime, Aitken buffering sustains brighter, more homogeneous clouds for longer. Plain Language Summary: Aerosols, small particles in the atmosphere associated with ocean biology, sea spray, land, and human‐produced emissions, influence cloud brightness and, by suppressing precipitation and subsequent break up, cloud lifetime. Understanding aerosol‐cloud‐precipitation interactions is critical in understanding how aerosols influence the climate system. This study examines how the very smallest aerosol particles modify cloud formation, brightness, and lifetime over the North Atlantic ocean. We utilize a recent set of aircraft and satellite observations from a dedicated field campaign as well as a detailed model that resolves fine‐scale interactions important to cloud development. After comparing the model to real‐world observations, we test how modifying the amount of small particles impacts the cloud brightness and lifetime. We find that the small particles are able to offset precipitation removal of larger particles, helping clouds to last longer and stay brighter. Key Points: Observations of mid‐latitude decoupled low clouds constrain a large‐eddy simulation investigating aerosol‐cloud‐precipitation interactionsBoundary layer Aitken activation and turbulent and convective fluxes restore accumulation mode aerosols against precipitation lossesAitken buffering acts to sustain brighter, more homogeneous clouds for longer [ABSTRACT FROM AUTHOR]

The variability of the shortwave radiative fluxes at the surface and top of atmosphere (TOA) is examined in a pre‐industrial modeling setup using the Pacific Decadal Oscillation (PDO) as a possible pacemaker of atmospheric decadal‐scale variability. Within models from the Coupled Model Intercomparison Project—Phase 6, downwelling shortwave radiation at the surface, the net shortwave fluxes at the surface and TOA, as well as cloud radiative effects show remarkably similar patterns associated with the PDO. Through ensemble simulations designed with a pure PDO pattern in the North Pacific only, we show that the PDO relates to about 20%–40% of the unforced year‐to‐year variability of these shortwave fluxes over the Northern Hemispheric continents. The sea surface temperature imprint on shortwave‐flux variability over land is larger for spatially aggregated time series as compared to smaller areas, due to the blurring effect of small‐scale atmospheric noise. The surface and TOA radiative flux anomalies associated with the PDO index range of [−1.64; 1.64] are estimated to reach up to ±6 Wm−2 for North America, ∓3 Wm−2 for India and ±2 Wm−2 for Europe. We hypothesize that the redistribution of clouds in response to a North Pacific PDO anomaly can impact the South Pacific and North Atlantic SSTs. Plain Language Summary: We investigate how solar radiation at Earth's surface and the top of the atmosphere, which are mainly controlled by cloudiness, can vary over decades as a response to a horseshoe pattern typical for the North Pacific sea surface temperatures (SSTs)—the Pacific Decadal Oscillation (PDO). We use idealized climate model simulations to show that about a third of the year‐to‐year changes in solar radiation over the Northern Hemispheric continents are related to this phenomenon. These changes are more noticeable when looking at large areas rather than small ones, as high frequency smaller scale atmospheric variations can obscure the bigger picture. By keeping the PDO fixed to a constant negative value, implying below average cold sea surface temperatures off the western coast of North America and warmer than average temperatures toward Japan, we show that North America and Europe exhibit a reduction in cloudiness, while clouds increase in India. The same with an opposite sign is true for a positive PDO anomaly. These changes in cloud patterns might further affect SSTs in the South Pacific and North Atlantic oceans. Key Points: The Pacific Decadal Oscillation (PDO) is a prominent pacemaker for variability, accounting for about 1/3 of the shortwave flux year‐to‐year variability over NH continentsA negative PDO anomaly leads to a reduction in atmospheric shortwave reflectivity (clouds) in North America and Europe and an increase in IndiaThe redistribution of clouds in response to a North Pacific PDO anomaly might influence SSTs in the South Pacific and North Atlantic [ABSTRACT FROM AUTHOR]

A continuous decrease in aerosols over the Western North Atlantic Ocean (WNAO) on a decadal timescale provides a long‐term benchmark to evaluate how various natural and anthropogenic processes affect the manifestation of aerosol‐cloud interactions in this region. Furthermore, the WNAO serves as a natural laboratory with diverse aerosol sources, marine boundary layer clouds more variable than those in marine stratocumulus deck regions, and unique flow regimes established by the Gulf Stream and the semi‐permanent Bermuda High. We investigate how satellite‐retrieved macrophysical and microphysical properties of low clouds and the surface shortwave irradiance changed from 2003 to 2020, in tandem with this aerosol decrease. The decadal changes in large‐scale meteorology related to the North Atlantic Oscillation (NAO) are also examined. We find a reduction in low‐cloud optical thickness, accompanied by fewer and larger cloud droplets, yet observe no significant changes in low‐cloud fraction and liquid water path. Despite the reduction in low‐cloud optical thickness together with aerosol decrease, a corresponding increase in the trends of surface shortwave irradiance, also known as surface brightening, is lacking. This absence of brightening is potentially related to concomitant changes found in large‐scale meteorology associated with NAO—Bermuda High strengthening, sea surface warming, and atmospheric moistening— as well as an increase in high‐level cloud fraction that can counteract the surface brightening. Ultimately, our findings suggest that spatial patterns of decadal meteorological variability introduce complexities in the surface cloud radiative effect over the WNAO, thereby complicating the isolation and examination of aerosol‐cloud interactions. Plain Language Summary: Over recent decades, the Western North Atlantic Ocean has experienced a steady decrease in aerosols—tiny particles in the air. This situation offers a chance to study how natural phenomena and human activities influence cloud‐aerosol interactions. The area is known for its diverse aerosol sources, complex cloud types, and distinct oceanic and atmospheric flow patterns influenced by the Gulf Stream and Bermuda High. By analyzing satellite data from 2003 to 2020, we investigated how low‐lying clouds and sunlight penetration have changed in response to fewer aerosols, and how the North Atlantic Oscillation (NAO) affects weather patterns. Our findings show that while low‐lying clouds have become more transparent with fewer, larger droplets, their coverage and juiciness have not changed significantly. Contrary to expectations, these changes have not lead to an increase in sunlight reaching the Earth's surface, a phenomenon known as "surface brightening." This could be due to NAO‐related warmer sea surfaces, increased moisture, and more high‐level clouds, which might obscure any brightening. Our study shows that weather shifts in the Western North Atlantic Ocean add complexity to understanding how clouds influence sunlight, challenging the study of aerosol‐cloud interactions. Key Points: In tandem with the continuous decrease in aerosol, low‐cloud droplets became fewer and larger over the western North AtlanticDespite concurrent changes in aerosol and low‐cloud optical properties, surface shortwave irradiance lacked reciprocal significant trendsMeteorological fields—temperature and humidity—correlated with the North Atlantic Oscillation had changed, exhibiting tripolar patterns [ABSTRACT FROM AUTHOR]

In situ and spaceborne studies reveal the prevalence of thin clouds in the major Stratocumulus‐to‐Cumulus Transition (SCT) regions. Using instantaneous satellite and reanalysis data, this study investigates the properties of thin clouds in the Southeast Pacific Ocean and their impact on the cloud radiative effect (CRE). Our findings demonstrate that thin clouds are intrinsic to the SCT. The overcast stratocumulus‐dominated regime exhibits a minimal presence of thin clouds, which become notably prominent after the clouds breakup into the cumulus‐dominated regime. The regime dependence of the occurrence of thin clouds is also observed in terms of the marine cold‐air outbreak parameter and the sea surface temperature. Thin clouds at a given cloud cover significantly modulate the shortwave (SW) and longwave (LW) components of CRE. SW CRE decreases by 46 %–65 % with increasing thin cloud cover. They account for a larger variance in cloud albedo than the combined influence of the liquid water path and effective radius. Furthermore, LW CRE decreases by about 12 %–52 % with thin cloud cover. An increase in the fraction of thin clouds also leads to a larger fraction of negative SW CRE offset by positive LW CRE at a given cloud cover. This LW compensation ranges from approximately 8 % at overcast cloud cover to as much as 19 % at about 50 % cloud cover. These findings elucidate the crucial role of thin clouds, and thus cloud morphology, in modulating CRE and underscore the necessity of their accurate representation in climate models. Plain Language Summary: The eastern regions of major global oceans are primarily covered by low‐altitude clouds. These bright clouds overlay the dark ocean surface, reflecting incoming solar radiation and cooling the Earth. Concurrently, they act as a barrier to the energy emitted by the ocean surface, preventing it from escaping the Earth and thereby contributing to the Earth's warming. Satellite observations reveal the prevalence of thin clouds in these oceanic regions. In contrast to their thicker counterparts, thin clouds are less effective in reflecting solar radiation and blocking surface emissions. This study investigates the impact of thin clouds on radiation using data from various sources. We show that the presence of thin clouds significantly reduces cloud brightness by approximately 46 %–65 %, even when the cloud cover remains constant. Thin clouds have a more substantial effect on a cloud's ability to reflect solar radiation compared to the combined influence of cloud water and cloud droplet size. Furthermore, since thin clouds allow some surface emissions to pass through, their presence at a constant cloud cover reduces their warming effect by up to 52 %. These findings emphasize the crucial role of thin clouds in shaping the contribution of clouds to Earth's energy balance. Key Points: Thin clouds dim cloud brightness by up to 65 percent at a fixed cloud coverThin clouds exert a greater influence on cloud albedo than the combined effects of cloud water and droplet size under constant cloud coverThin clouds reduce longwave warming by up to 52 percent and modulate the balance between longwave warming and shortwave cooling [ABSTRACT FROM AUTHOR]

Earth may have been globally ice‐covered at least two times during the Cryogenian Period (720–635 Ma). Previous studies showed that clouds could strongly warm a hard snowball Earth and promote its deglaciation. However, the understanding of clouds was largely based on coarse‐resolution global simulations with parameterized convection and clouds, or high‐resolution cloud‐resolving simulations with explicit convection and clouds but limited to a small domain without the effects of large‐scale circulation. Here we present the first global non‐hydrostatic high‐resolution (30 km) simulation to investigate snowball clouds and their radiative effects. We show that spatial‐temporal cloud distributions exhibit clear meanders (patterns of curved lines rather than straight lines along the west‐east direction) and strong variabilities, which result from the tight interactions among the Inter‐Tropical Convergence Zone, Hadley cells, and baroclinic instability. The net cloud radiative effect is around 20 W m−2 in the tropics, consistent with previous global general circulation model simulations. Plain Language Summary: Earth may have been globally covered by snow and ice during the Cryogenian Period and is known as a hard snowball Earth, which is radically different from modern Earth. Using a global non‐hydrostatic high‐resolution model, within which vertical velocity and clouds are largely explicitly resolved, we find that the clouds on the hard snowball Earth show a more meandering pattern than modern Earth. Meanwhile, our results confirm the warming effect of snowball clouds, implying a lower CO2 concentration to terminate the global glaciation. Key Points: Snowball climate is simulated by a global non‐hydrostatic high‐resolution modelFine structures of clouds, Inter‐Tropical Convergence Zone, Hadley cells, and baroclinic eddies are clearly resolvedOur simulations confirm that clouds have a net warming effect on a hard snowball Earth [ABSTRACT FROM AUTHOR]

Abstract Over the past 30 years, the Arctic Dipole Anomaly (DA) has repeatedly led to record lows in summer sea ice extent, with cloud radiative effects (CRE) playing a crucial regulatory role. Here, we reveal the CRE variations between positive and negative DA events and elucidate the slowing impacts of CRE on sea ice thickness (SIT) changes. The DA triggers robust meridional winds and transpolar drift, markedly reducing SIT in the Beaufort Sea (BeS), Chukchi Sea (CS), and East Siberian Sea (ESS), while increasing it in the Greenland Sea (GS). CRE significantly slow SIT changes, contributing +14.4, +4.4, +16.4, and −26.7 cm to changes from June to August, against total changes of −55.9, −29.4, −39.8, and +42.8 cm in September over BeS, CS, ESS, and GS, respectively. This study underscores the key impacts of CRE on sea ice variation, emphasizing their significance in the polar climate system.

The Southern Annular Mode (SAM) is the most dominant natural mode of variability in the mid‐latitudes of the Southern Hemisphere (SH). However, both the sign and magnitude of the feedbacks from the diabatic processes, especially those associated with clouds, onto the SAM remain elusive. By applying the cloud locking technique to the Energy Exascale Earth System Model (E3SM) atmosphere model, this study isolates the positive feedback from the cloud radiative effect (CRE) to the SAM. Feedback analysis based on a wave activity‐zonal momentum interaction framework corroborates this weak but positive feedback. While the magnitude of the CRE feedback appears to be secondary compared to the feedbacks from the dry and other diabatic processes, the indirect CRE effects through the interaction with other dynamical and thermodynamical processes appear to play as important a role as the direct CRE in the life cycle of the SAM. The cross‐EOF analysis further reveals the obstructive effect of the interactive CRE on the propagation mode of the SH zonal wind directly through the CRE wave source and/or indirectly through modulating other diabatic processes. As a result, the propagation mode becomes more persistent and the SAM it represents becomes more predictable when the interactive CRE is disabled by cloud locking. Future efforts on inter‐model comparisons of CRE‐denial experiments are important to build consensus on the dynamical feedback of CRE. Plain Language Summary: The annular mode is the most dominant mode of variability in the mid‐latitude atmospheric circulation system. Its origin, maintenance, and feedback mechanisms have long been the focus of atmospheric dynamics research. While its dry mechanisms are well understood, the role of the diabatic processes in the midlatitude storm tracks, especially the radiative effects of the cloud fields that evolve together with the storms, have not been quantified. Even the sign of the diabatic feedback to the annular mode remains a topic of debate. By disabling the cloud radiative feedback through a cloud‐locking technique that decorrelates the cloud fields with other dry and moist components in an atmospheric model, we are able to isolate the cloud radiative effect (CRE) throughout the life cycle of the Southern Annular Mode (SAM). Compared to the case with interactive CRE, the propagating SAM becomes more persistent and predictable in the cloud‐locking run, although the overall diabatic feedback to the standing dipole representation of the SAM is somewhat attenuated in this run. The diabatic and CRE feedbacks to the SAM identified here epitomize the sensitivity of the leading mode of the atmospheric variability to the model representation of the diabatic processes. Key Points: Cloud locking technique is used to isolate the interactive cloud radiative effect (CRE) on the Southern Annular Mode (SAM)Cloud radiative effect boosts the persistence of SAM as the leading EOF of the Southern Hemisphere zonal windThe interactive CRE feedback acts to weaken the cross‐EOF interaction and counter the poleward propagation of the zonal wind [ABSTRACT FROM AUTHOR]

Tropical upper-level clouds (TUCs) control the radiation budget in a climate system and strongly influence surface temperatures. This study examines global mean surface temperature changes due to the percent change in TUC cover, which is referred to as the tropical upper-level cloud radiative effect (TUCRE, in units of Kelvin per %). We use a radiative-convective equilibrium model that can control both upper- and lower-level cloud layers separately in three idealized regions (extratropics, tropical moist, and tropical dry regions) and two sub-regions (clear-moist and cloudy-moist regions) within the tropical moist regions. In the simulation, tropical reflectivity based on the TUC fraction assumes a primary role in determining the TUCRE. Accurate estimate of the TUCRE requires careful prescriptions according to actual satellite observations. We use the extent of TUC fraction and reflectivity obtained from 18 years (2003–2020) of satellite data on daily MODIS cloud properties. Our results show that the estimated net TUCRE ranges from 0.19 to 0.33 K/%, with a higher TUC fraction leading to higher temperatures (a warming effect) in the climate system. This means that a longwave TUCRE dominates over a shortwave TUCRE. When upper- and lower-level clouds interplay in the model, the range of the TUCRE was greater with a combination of two cloud layers, although all values were positive. The TUCRE is greater by 0.22 to 0.40 K/% when upper- and lower-level clouds are negatively coupled, because the Earth warms due to a decline in the reflectance of solar radiation. When upper- and lower-level clouds are positively coupled, the TUCRE is lower by 0.14 to 0.30 K/%, as less radiation reaches the Earth through combined cloud layers. Finally, we test the sensitivity of the TUCRE with five TUC fractions and 15 combinations of tropical reflectivity. Comparing our results with the TUCREs estimated from climate models will help us understand how TUC cover affects climate, and should greatly reduce uncertainty associated with cloud feedback. [ABSTRACT FROM AUTHOR]

Spherical harmonic (SH) expansion is a useful tool to study any variable that has valid values at all latitudes and longitudes. The variable can be quantified as a sum of different spherical harmonic components, which are the spherical harmonic functions multiplied by their expansion coefficients. We find that the SH components of cloud radiative effect (CRE) have correlations with El Niño‐Southern Oscillation (ENSO) and the Hadley Circulation (HC). In particular, the expansion degree 2 (l=2 $l=2$) SH power spectrum component anomaly of CRE is strongly correlated with ENSO. The two dipole patterns appearing in the l=2 $l=2$ SH component anomaly map can be reasonably explained by a known mechanism of ENSO's impact on cloud properties. The l=3 $l=3$ and l=5 $l=5$ SH power spectrum components are correlated with HC intensity, whereas the l=6 $l=6$ and l=8 $l=8$ components are correlated with HC latitudinal widths. In ENSO warm and cold phases, the HC‐correlated SH components have opposite anomalies, which suggests the impact of ENSO on HC. This study illustrates that the SH expansion technique provides a different perspective to study the impacts of large‐scale atmospheric circulation on global cloud properties and radiative effects. Plain Language Summary: Clouds are a critical atmospheric constituent in regulating earth's energy budget (controlling the global temperature) by reflecting incident sunlight (a cooling effect), and emitting radiation to the ground (warming below clouds) and to space. The net warming or cooling effect of these factors is called the cloud radiative effect (CRE). The CRE varies with ordinary climate oscillations such as the well‐known El Niño‐Southern Oscillation (ENSO), and may amplify or partly suppress long‐term global warming depending on whether cloud cover diminishes or increases. This study tests a way to summarize global cloud property variations, observed in great detail by satellites, in terms of various two‐dimensional characteristic patterns defined by the spherical harmonic functions. For example, ENSO variations can be clearly observed in one of the characteristic patterns of CRE changes. Key Points: Spherical harmonic functions can be used to accurately depict global cloud propertiesDegree 2 spherical harmonic component anomaly of cloud radiative effect is correlated with El Niño‐Southern OscillationDegrees 3 to 8 spherical harmonic components of cloud radiative effect are correlated with Hadley Circulation [ABSTRACT FROM AUTHOR]

Abstract Spherical harmonic (SH) expansion is a useful tool to study any variable that has valid values at all latitudes and longitudes. The variable can be quantified as a sum of different spherical harmonic components, which are the spherical harmonic functions multiplied by their expansion coefficients. We find that the SH components of cloud radiative effect (CRE) have correlations with El Niño‐Southern Oscillation (ENSO) and the Hadley Circulation (HC). In particular, the expansion degree 2 (l=2 $l=2$) SH power spectrum component anomaly of CRE is strongly correlated with ENSO. The two dipole patterns appearing in the l=2 $l=2$ SH component anomaly map can be reasonably explained by a known mechanism of ENSO's impact on cloud properties. The l=3 $l=3$ and l=5 $l=5$ SH power spectrum components are correlated with HC intensity, whereas the l=6 $l=6$ and l=8 $l=8$ components are correlated with HC latitudinal widths. In ENSO warm and cold phases, the HC‐correlated SH components have opposite anomalies, which suggests the impact of ENSO on HC. This study illustrates that the SH expansion technique provides a different perspective to study the impacts of large‐scale atmospheric circulation on global cloud properties and radiative effects.

Overlying cloud can affect the radiative and precipitation features of underlying cloud via its radiative and seeding effects. Using 4 years of CALIPSO and CloudSat observations, this study demonstrates that overlying clouds usually suppress the vertical development of underlying stratocumulus (Sc) by their radiative effect, thus reducing the precipitation, cloud liquid water path and thickness of Sc on a global scale. The radiative effect intensity increases with increasing optical depth (COD) of overlying cloud and decreasing cloud distance between cloud layers. By dividing the overlying clouds into seeder and non‐seeder groups, we find that seeding by overlying clouds can partly or even totally offset the precipitation suppression caused by their radiative effect. The net effect on precipitation of Sc switches from suppression to enhancement when COD of overlying cloud exceeds 0.16. This finding indicates that the competition between radiative and seeding effects of overlying cloud should be considered in cloud‐precipitation interaction. Plain Language Summary: Overlying cloud can influence the development of underlying cloud through seeding and radiative effects. However, our understanding of the competition between the two effects of overlying clouds on marine stratocumulus (Sc) and how they affect the energy budget and water cycle remains limited. Using 4 years (2007–2010) of satellite observations, we find that the global net effect of overlying clouds on underlying Sc suppresses the vertical development of the Sc, thus reducing the precipitation rate, cloud liquid water path, and cloud thickness. When the optical depth of the overlying cloud (COD) is larger and the cloud distance between the two cloud layers is smaller, the radiative effect is stronger. By identifying double‐layer cloud systems with upper‐layer cloud seeding, the dependency of the net effect on overlying cloud properties and cloud‐top longwave cooling rate difference between the double‐ and single‐layered Sc clouds is further quantified. Seeding by the overlying cloud can enhance the precipitation and offset the precipitation suppression of the radiative effect. The net effect on precipitation switches from suppression to enhancement when the COD > 0.16. This finding indicates that the seeding effect of overlying cloud and its variation should be considered in the parameterization of cloud–precipitation interactions. Key Points: Competition between the radiative and seeding effects of overlying clouds on stratocumulus (Sc) is quantified at a global scaleThe global net effect of overlying clouds suppresses the vertical development and thus reduces precipitation of underlying ScThicker seeder clouds (optical depth >0.16) can reverse the change in Sc precipitation from radiative suppression to seeding enhancement [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Clouds are a dominant modulator of the energy budget. The cloud shortwave radiative effect at the surface (CRE) is closely related to the cloud macro- and micro-physical properties. Systematic observation of surface irradiance and cloud properties are needed to narrow uncertainties in CRE. In this study, 1-min irradiance and Total Sky Imager measurements from 2005 to 2009 at Xianghe in North China Plain are used to estimate cloud types, evaluate cloud fraction (CF), and quantify the sensitivities of surface irradiance with respect to changes in CF whether clouds obscure the sun or not. The annual mean CF is 0.50, further noting that CF exhibits a distinct seasonal variation, with a minimum in winter (0.37) and maximum in summer (0.68). Cumulus occurs more frequently in summer (32%), which is close to the sum of the occurrence of stratus and cirrus. The annual CRE is −54.4 W m−2, with seasonal values ranging from −29.5 W m−2 in winter and −78.2 W m−2 in summer. When clouds do not obscure the sun, CF is a dominant factor affecting diffuse irradiance, which in turn affects global irradiance. There is a positive linear relationship between CF and CRE under sun-unobscured conditions, the mean sensitivity of CRE for each CF 0.1 increase is about 1.2 W m−2 [79.5° < SZA (Solar Zenith Angle) < 80.5°] to 7.0 W m−2 (29.5° < SZA < 30.5°). When clouds obscure the sun, CF affects both direct and diffuse irradiance, resulting in a non-linear relationship between CF and CRE, and the slope decreases with increasing CF. It should be noted that, although only data at Xianghe is used in this study, our results are representative of neighboring areas, including most parts of the North China Plain. [ABSTRACT FROM AUTHOR]

The surface longwave downward radiation (SLDR) is the crucial input parameter for many land surface process models. To address the unavailability of the official cloudy-sky SLDR product of the FengYun-4A (FY-4A) satellite, this study developed an integrated framework to estimate the hourly all-time cloud-sky SLDR from the advanced geostationary radiation imager (AGRI) onboard FY-4A. Firstly, we developed a novel method that directly estimate the all-time cloud base height (CBH) by the Light Gradient Boosting Machine technique and achieved an accurate CBH estimate. Subsequently, the cloud base temperature (CBT), calculated from the estimated CBH and MARRA2 temperature profiles, was used to drive a single-layer cloud model (SLCM) and realize the cloudy-sky SLDR estimate. Validation results across 51 flux sites showed the bias and RMSE of the estimated all-time cloudy-sky SLDR are −0.06 and 22.61 W/m2, respectively, outperforming mainstream SLDR products. In addition, the CBT-based SLCM performed well under different cloud types, elevations, and land types, demonstrating the robustness and generalizability of the integrated framework for estimating the all-time cloudy-sky SLDR. • We propose an integrated framework to estimate all-time cloud-sky SLDR for FY 4A/AGRI. • A novel direct retrieval method is developed to estimate AGRI CBH during both daytime and nighttime. • The bias and RMSE of the derived cloudy sky SLDR over 51 sites located in East Asia are −0.06 W/m2 and 22.61 W/m2. • This study provides an alternative solution for AGRI which does not have the cloudy-sky SLDR product yet. [ABSTRACT FROM AUTHOR]

Satellite images show solid marine stratocumulus cloud decks (Sc) that break up over the remote oceans. The Sc breakup is initiated by precipitation and is accompanied by a strong reduction in the cloud radiative effect. Aerosol has been shown to delay the Sc breakup by postponing the onset of precipitation, however its climatic effect is uncertain. Here we introduce a new approach that allows us to re‐cast currently observed cloud cover and albedo to their counterfactual cleaner world, enabling the first estimate of the radiative effect due to delayed cloud breakup. Using simple radiative approximation, the radiative forcing with respect to pre‐industrial times due to delayed Sc breakup is −0.39 W m−2. The radiative effect changes nearly linearly with aerosol due to the droplet concentration control on the cloud cover, suggesting a potentially accelerated warming if the current trend of reduction in aerosol emissions continues. Plain Language Summary: The response of cloud cover to aerosol is a climatologically important quantity that has been extremely difficult to estimate. The challenge is that one would need to estimate the fractional area that is currently overcast, but which would have been partly overcast in a cleaner atmosphere. Global climate models (GCMs) are one tool to address such a problem. They allow one to change aerosol levels and to evaluate the cloud response. However, representation of warm, low‐level cloud processes, and in particular aerosol‐cloud interactions in GCMs, is inadequate. Here we introduce an observational method that allows us to re‐cast the currently observed cloud cover and albedo of oceanic warm clouds to their counterfactual state in a cleaner world. We find a linear relationship between the cloud radiative effect and droplet concentration. If we continue to experience a decrease in aerosol emissions then we anticipate a reduction in the aerosol‐cloud radiative effect. The global annual radiative forcing associated with anthropogenic aerosol delaying closed cell breakup is found to be −0.39 W m−2. Key Points: A simple model is presented to describe closed cell breakup by initiation of precipitationThe model demonstrates that the global annual radiative effect due to delayed closed cells breakup changes nearly linearly with emissionsThe linearity emerges from the nearly linear relationship between cloud cover and albedo [ABSTRACT FROM AUTHOR]

Long believed to be insignificant, melt activity on the Northeast Greenland Ice Stream (NEGIS) has increased in recent years. Summertime Arctic clouds have the potential to strongly affect surface melt processes by regulating the amount of radiation received at the surface. However, the cloud effect over Greenland is spatially and temporally variable and high‐resolution information on the northeast is absent. This study aims at exploring the potential of a high‐resolution configuration of the polar‐optimized Weather Research & Forecasting Model (PWRF) in simulating cloud properties in the area of the Nioghalvfjerdsfjorden Glacier (79 N Glacier). Subsequently, the model simulations are employed to investigate the impact of Arctic clouds on the surface energy budget and on surface melting during the extensive melt event at the end of July 2019. Compared to automatic weather station (AWS) measurements and remote‐sensing data (Sentinel‐2A and the Moderate Resolution Imaging Spectroradiometer, MODIS), PWRF simulates cloud properties with sufficient accuracy. It appears that peak melt was caused by an increase in solar radiation and sensible heat flux (SHF) in response to a blocking anticyclone and foehn winds in the absence of clouds. Cloud warming over high‐albedo surfaces helped to precondition the surface and prolonged the melting as the anticyclone abated. The results are sensitive to the surface albedo and suggest spatiotemporal differences in the cloud effect as snow and ice properties change over the course of the melting season. This demonstrates the importance of including high‐resolution information on clouds in analyses of ice sheet dynamics. [ABSTRACT FROM AUTHOR]

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Accurate prediction of cloud radiative effect (CRE) is important to weather forecast and climate projection, and solar energy production—a major renewable energy source toward decarbonization. Here, we evaluate the capability of the Weather Research and Forecast (WRF) model to simulate solar irradiance on a short‐term timescale (days) against observations in a remote region in north China. Results illustrate that our WRF simulation systematically underestimates the CRE and three error sources are identified: (a) incorrectly predicted cloud occurrence (i.e., missed clouds and false clouds), (b) underestimated cloud condensate mass, and (c) simplified parameterization of solar irradiance extinction. The incorrect cloud occurrence is the leading bias source, because it occurred most frequently and results in a substantial magnitude of errors. The cloud occurrence bias is subject to simulations of large‐scale air ascends and planetary boundary layer turbulence. Even when cloud occurrence is correctly simulated, our WRF simulation still underestimates CRE. This is because (a) the shallow convection scheme and cloud microphysics scheme underestimate cloud condensate mass and (b) cloud water path that feeds in the radiation scheme neglects precipitating cloud condensates (i.e., raindrops and graupels). Furthermore, an evaluation of cases with small bias in cloud condensate mass and effective radius demonstrates the parameterization of solar irradiance extinction for clouds induces a mean root mean square deviation of 110 W/m2. A possible reason is the simplified calculation of cloud extinction efficiency by applying Monte Carlo integration. The gained knowledge is important for understanding CRE simulation and solar irradiance forecast. Key Points: The Weather Research and Forecast model simulation is found to underestimate cloud radiative effect (CRE) in a remote and semiarid regionMissed clouds and false clouds, that occur 50% of the time and cause up to 400 W/m2 bias in CRE, are the leading bias sourcesOther nonignorable bias sources include underestimated cloud condensate mass and the oversimplified radiative transfer scheme [ABSTRACT FROM AUTHOR]

Based on 12 years (March 2000–February 2012) of monthly data from Clouds and the Earth's Radiant Energy System energy balanced and filled (CERES-EBAF), this study systematically evaluates the applicability of Advanced Very High Resolution Radiometer (AVHRR) and second Along-Track Scanning Radiometer and advanced ATSR (AATSR) flux products at the top-of-the-atmosphere (TOA), and the ability of atmosphere-only simulations of the Coupled Model Intercomparison Project Phase6 (CMIP6/AMIP) model in reproducing the observed spatial–temporal patterns of TOA cloud radiative effect (CRE) over the Tibetan Plateau (TP). Results show that TOA radiative fluxes from AVHRR and AATSR can be used to analyze their spatial/temporal characteristics over TP region, especially for AVHRR, but none of them can capture the observed CRE trend since 2000. In particular, when using AATSR TOA radiative flux in clear-sky of TP, the large bias of SW flux (regional mean about 30.48 Wm−2) compared with CERES-EBAF must be taken seriously. The multimodel ensemble mean (MEM) can sufficiently reproduce the temporal changes of CREs, particularly the shortwave CRE. Regarding the geographical pattern of CREs of MEM, the annual mean deviations of longwave CRE are very small, while obvious underestimations can be found in the southeastern TP for shortwave CRE. Additionally, the spatial distribution of CREs is difficult to reproduce for many individual models due to albedo and temperature biases of surface. Our results also demonstrated that MEM still has evident difficulties to capture realistic CRE trends in TP due to poor simulations in surface and cloud properties (particularly cloud fraction). [ABSTRACT FROM AUTHOR]

Clouds are largely responsible for the spread of climate models predictions. Here we focus on the uncertainties in cloud shortwave radiative effect due to the parameterization of liquid cloud single scattering properties (SSPs) from liquid water content (LWC) and droplet number concentration (N), named parameterization of cloud optical properties. Uncertainties arise from not accounting for the droplet size distribution (DSD)—which affects the estimation of the effective radius (reff) and modulates the reff‐dependency of the SSPs—and from averaging SSPs over wide spectral bands. To assess these uncertainties a series of reff‐dependent SSPs parameterizations corresponding to various DSDs and spectral averaging methods are derived and implemented in a radiative code. Combined with the DSD‐dependent estimation of reff they are used to compute the bulk radiative properties (reflectance, transmittance, absorptance) of various clouds (defined in terms of LWC and N), including a homogeneous cloud, more realistic case studies, and outputs of a climate model. The results show that the cloud radiative forcing can vary up to 20% depending on the assumed DSD. Likewise, differences up to 20% are obtained for heating rates. The estimation of reff is the main source of uncertainty, while the SSPs parameterization contributes to around 20% of the total uncertainty. Spectral averaging is less an issue, except for atmospheric absorption. Overall, global shortwave cloud radiative effect can vary by 6 W m−2 depending on the assumed DSD shape, which is about 13% of the best observational estimate. Plain Language Summary: Climate predictions differ a lot from one model to another, and the difficulty to simulate how clouds will behave in a warmer world is largely responsible for that. The radiative effect of clouds depends on the size of the individual droplets forming a cloud, a quantity that is not explicitly represented in climate models. In this study we investigate how not accounting for the detailed droplet size distribution affects the capability of climate models to reliably predict the radiative effect of clouds. By assuming a variety of droplet size distributions in a set of simulations, we observe that apparently similar clouds in climate models can have very different radiative impacts depending on the assumed distribution. This is primarily attributed to the estimation of the effective radius of cloud droplets, a key quantity that drives cloud radiative properties. Differences up to 20% are observed on critical quantities such as fluxes at top‐of‐atmosphere and at the surface. The absorption of radiation within clouds is also significantly altered. The impact on the global estimate of shortwave cloud radiative effect is around 13%, which highlights the need to improve the representation of the microphysical characteristics of clouds to run more reliable climate predictions. Key Points: The estimation of cloud single scattering properties (SSPs) is affected by not accounting for the droplet size distribution (DSD) and by spectral averaging over wide bandsThe impact of the DSD shape on the estimation of reff is significant, and slightly offset by the weak dependency of SSPs to DSD shapeThe global cloud radiative effect simulated by a climate model can vary up to 13% depending on the assumed DSD [ABSTRACT FROM AUTHOR]

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. Plain Language Summary: Anomalous surface warming in the Siberian Arctic was observed in spring 2020. The key question is what caused the surface warming. Here, we show that this surface warming in the Siberian Arctic is likely caused by the local severe ozone loss, along with the ice‐albedo feedback. The reduction of stratospheric ozone leads to lower stratospheric cooling and a decrease in the static stability in the upper troposphere, which results in an increase in high clouds. It consequently causes an increase of surface longwave radiation and enhanced surface warming in April and May. The ice‐albedo feedback further amplifies surface warming. Key Points: Both severe ozone loss and surface warming over the Siberian Arctic were observed in the spring of 2020The ozone loss in the Siberian Arctic may contribute to the most of the surface warming in April by modifying the cloud radiative effectsIce‐albedo feedback further amplifies the surface warming in April and May [ABSTRACT FROM AUTHOR]

Regional responses to surface warming are strongly influenced by the availability of surface or atmospheric moisture. For example, differences in evapotranspiration, atmospheric temperature lapse rate and heat capacity due to the availability of water over oceans and its lack over land contribute to an observed land/ocean warming ratio that is greater than one. This study shows that mechanisms related to the distributions of soil or atmospheric moisture could result in variations in regional climate change over land in the tropics and subtropics. Using atmospheric reanalyses and observations for the satellite era (1979–2016) within ±30° latitude, the analysis shows that dry regions such as northern and southern Africa and south‐central Australia have a significant negative regional spatial correlation between time‐averaged soil moisture/evapotranspiration and surface temperature trends. In contrast, wet tropical regions such as Amazonia and the Congo Basin display a significant positive spatial correlation between these quantities. Spatial correlations suggest that a regional amplification of surface temperature trends in wet regions could be associated with a robust positive longwave radiative effect of high clouds which co‐occur with wet soils. This positive relationship is strongest during austral summer, dominated by the summer seasons in the Amazon and Congo basins. These differences in regional sensitivity to greenhouse gas warming can be consequential for regional climate change assessment, for both tropical forests, which could already be operating at their high temperature limit, and also for dry desert regions, which are already marginal for supporting life. [ABSTRACT FROM AUTHOR]

Abstract The cloud parameterizations of the LMDZ6A climate model (the atmospheric component of the IPSL‐CM6 Earth system model) are entirely described, and the global cloud distribution and cloud radiative effects are evaluated against the CALIPSO‐CloudSat and CERES observations. The cloud parameterizations in recent versions of LMDZ favor an object‐oriented approach for convection, with two distinct parameterizations for shallow and deep convection and a coupling between convection and cloud description through the specification of the subgrid‐scale distribution of water. Compared to the previous version of the model (LMDZ5A), LMDZ6A better represents the low‐level cloud distribution in the tropical belt, and low‐level cloud reflectance and cover are closer to the PARASOL and CALIPSO‐GOCCP observations. Mid‐level clouds, which were mostly missing in LMDZ5A, are now better represented globally. The distribution of cloud liquid and ice in mixed‐phase clouds is also in better agreement with the observations. Among identified deficiencies, low‐level cloud covers are too high in mid‐latitude to high‐latitude regions, and high‐level cloud covers are biased low globally. However, the cloud global distribution is significantly improved, and progress has been made in the tuning of the model, resulting in a radiative balance in close agreement with the CERES observations. Improved tuning also revealed structural biases in LMDZ6A, which are currently being addressed through a series of new physical and radiative parameterizations for the next version of LMDZ.

The cloud parameterizations of the LMDZ6A climate model (the atmospheric component of the IPSL‐CM6 Earth system model) are entirely described, and the global cloud distribution and cloud radiative effects are evaluated against the CALIPSO‐CloudSat and CERES observations. The cloud parameterizations in recent versions of LMDZ favor an object‐oriented approach for convection, with two distinct parameterizations for shallow and deep convection and a coupling between convection and cloud description through the specification of the subgrid‐scale distribution of water. Compared to the previous version of the model (LMDZ5A), LMDZ6A better represents the low‐level cloud distribution in the tropical belt, and low‐level cloud reflectance and cover are closer to the PARASOL and CALIPSO‐GOCCP observations. Mid‐level clouds, which were mostly missing in LMDZ5A, are now better represented globally. The distribution of cloud liquid and ice in mixed‐phase clouds is also in better agreement with the observations. Among identified deficiencies, low‐level cloud covers are too high in mid‐latitude to high‐latitude regions, and high‐level cloud covers are biased low globally. However, the cloud global distribution is significantly improved, and progress has been made in the tuning of the model, resulting in a radiative balance in close agreement with the CERES observations. Improved tuning also revealed structural biases in LMDZ6A, which are currently being addressed through a series of new physical and radiative parameterizations for the next version of LMDZ. Plain Language Summary: This paper describes the representation of clouds in the latest version of LMDZ, which is a French atmospheric model used for climate change projections. Along with other international climate models, it serves as a basis for the IPCC (Intergovernmental Panel on Climate Change) report by contributing to the CMIP project (Climate Model Intercomparison Project). Clouds are especially important in the climate system because they reflect a lot of sunlight and also absorb and emit a lot of infrared radiation. They can either amplify or reduce the current global warming depending on their change in opacity, altitude, and detailed properties. It is therefore essential to represent them accurately in climate models. The main physical equations used to compute cloud properties in LMDZ are introduced, and the model results are compared to various satellite observations. It reveals that low‐level and mid‐level clouds are in better agreement with the observations than before but that high‐level clouds remain difficult to simulate realistically. Ongoing developments aimed at solving these remaining deficiencies are finally described. Key Points: Cloud parameterizations of the LMDZ6A climate model are entirely describedLow‐level and mid‐level cloud distribution and radiative effects are improved compared to LMDZ5ALMDZ6A is better tuned than LMDZ5A, and knowledge of its structural deficiencies has been gained [ABSTRACT FROM AUTHOR]

To better understand and quantify the impact of clouds on the Greenland Ice Sheet surface mass balance (SMB), we study the spatiotemporal variability of the cloud radiative effect (CRE). The total CRE is separated in short‐term and long‐term impacts by performing multiple simulations with the SNOWPACK model for 2001‐+2010. The annual total CRE is 16.8 ± 4.5 W m−2, reducing the SMB with −157 ± 3.8 Gt yr−1. Summer cloud radiative cooling is −6.4 ± 5.7 W m−2 in the ablation area, increasing the SMB with 121 ± 2.2 Gt yr−1. The annual integrated impact is cloud‐reduced SMB of −36 Gt yr−1. The short‐term effect dominates the opposing long‐term effects through the albedo‐melt feedback. A long‐term warming effect decreases the albedo and so preconditions the surface for enhanced (summer) melt. The impact of the CRE, determined by spatial, temporal and initial conditions, explains existing conflicted views on the role of cloud radiation and emphasizes the need for accurate cloud and albedo representations in future studies. Key Points: Total cloud radiative warming occurs year‐round, except in the ablation area during summerWhen cloud radiative cooling occurs, clouds reduce mass loss and dominate the impact on the surfaceShort‐term and long‐term cloud effects are opposite, governed by surface albedo changes [ABSTRACT FROM AUTHOR]

The global distribution of winter to winter sea surface temperature (SST) reemergence is analyzed using a novel metric based on an autoregressive 1 model, and the global impact of SST on cloud amount and cloud type are examined using satellite data. A region in the northeastern Pacific Ocean is identified where wintertime SSTs are correlated with the occurrence of marine stratiform cloud the following winter. This correlation is likely a manifestation of SST reemergence. We hypothesize that through this reemergence mechanism marine stratus cloud amount, and thus shortwave cloud radiative effect, in the northeastern Pacific exhibits memory on inter‐seasonal and even multi‐year time scales and that exploration of this relationship may provide insight into the SST—low cloud feedbacks. Plain Language Summary: Global satellite records of ocean temperature and cloudiness are compared, and one region in the North Pacific Ocean is identified where wintertime cloud amount is related to sea surface temperature from the prior winter. This is due to a combination of two well‐established effects: the strong link between low clouds and sea surface temperature, and sea surface temperature reemergence, a tendency for wintertime ocean temperatures to be influenced by ocean temperature from the previous winter. This relationship may be useful for understanding how cloud and sea surface temperature might interact in a changing climate. Key Points: Global patterns of SST reemergence and of cloud‐SST interaction are examinedOne region in the northeastern Pacific is identified where wintertime low cloud occurrence is correlated with the previous winter's SST [ABSTRACT FROM AUTHOR]

Ice crystals commonly adopt a horizontal orientation under certain aerodynamic and electrodynamic conditions that occur in the atmosphere. While the radiative impact of horizontally oriented ice crystals (HOIC) has been theoretically studied with respect to their impact on shortwave cloud albedo, the longwave impact remains unexplored. This work analyzes the occurrence of HOIC at Summit, Greenland, from July 2015 to June 2017. Using polarization lidar and ancillary atmospheric sensors, ice crystal orientations are identified and used to interpret cloud radiative impact on the surface radiation budget. We find HOIC occur in at least 25.6% of all ice‐only column observations. We find that the shortwave impact of HOIC is to increase cloud radiative effect by approximately 22% for a given solar zenith angle. We also find that the longwave impact of HOIC compared to randomly oriented ice crystals are statistically different at the p < 0.01 significance level, increasing the surface radiative effect by approximately 8% for clouds with infrared optical depths < ~1. We suggest that the observed difference between the surface radiative effect for clouds containing randomly oriented ice crystals and HOIC may be due to enhanced scattering, but this hypothesis needs to be further explored with more detailed observations and modeling. Plain Language Summary: Because of their shape, ice crystals can fall from clouds with a preferential horizontal orientation due to drag forces acting on their surfaces. Using novel remote sensing techniques, we identify the occurrence of preferentially oriented ice crystals and attempt to quantify the impact of ice crystal orientation on the surface environment at a field site in the Arctic. We observe, to our knowledge, for the first time, statistically significant differences in the radiative properties of ice clouds containing preferentially oriented ice crystals from those containing no detectable preferentially oriented ice crystals. We suggest a hypothesis that may explain this difference, but note it requires further testing to fully analyze and define methods to explore the mechanism further. Key Points: First long‐term observational study of the radiative importance of ice crystal orientation in the polar regions is presentedIce clouds containing oriented crystals show greater radiative effect than clouds without oriented crystals in the shortwave and longwaveObservations suggesting enhanced radiative effect of oriented ice crystals occurring in the longwave require further investigation [ABSTRACT FROM AUTHOR]

There was a dramatic increase in aerosol loading in China after the 1960s due to rapid industrialization, followed by a gradual reduction due to improvements in air quality since the early 2000s. They are deemed to be the main cause of ‘dimming’ and ‘brightening’ in China, respectively. China, therefore, provides an ideal testbed to investigate the multi-decadal evolution of clouds under a background of large variations in the amount of atmospheric aerosols. We used a unique combination of long-term in-situ observational records combined with a radiative transfer model to investigate the changes in clouds and aerosols over the last 60 years (1958–2018) over China. We found during the dimming period, the clouds over China shrunk in area steadily, gradually thinned in terms of optical depth, and thereby blocked less and less solar radiation. This situation reversed during the brightening period. The clouds over China showed a quick expansion in extent and thickening in terms of optical depth, and accordingly the amounts of solar radiation blocked by clouds recovered rapidly. It is observationally demonstrated that high levels of pollution and the associated amount of aerosols cause a suppression of cloud growth and a reduction of optical depth.

Current passive sensors fail to accurately identify cloud phase, thus largely limiting the quantification of radiative contributions and precipitation of different cloud phases over the Tibet Plateau (TP), especially for the mixed-phase and supercooled water clouds. By combining the 4 years of (January 2007–December 2010) cloud phase (2B-CLDCLASS-LIDAR), radiative fluxes (2B-FLXHR-LIDAR), and precipitation (2C-PRECIP-COLUMN) products from CloudSat, this study systematically quantifies the radiative contribution of cloud phases and precipitation over the TP. Statistical results indicate that the ice cloud frequently occurs during the cold season, while mixed-phase cloud fraction is more frequent during the warm season. In addition, liquid clouds exhibit a weak seasonal variation, and the relative cloud fraction is very low, but supercooled water cloud has a larger cloud distribution (the value reaches about 0.24) than those of warm water clouds in the eastern part of the TP during the warm season. Within the atmosphere, the ice cloud has the largest radiative contribution during the cold season, the mixed-phase cloud is the second most important cloud phase for the cloud radiative contribution during the warm season, and supercooled water clouds’ contribution is particularly important during the cold season. In particular, the precipitation frequency over the TP is mainly dominated by the ice and mixed-phase clouds and is larger over the southeastern part of the TP during the warm season.

This study reviews the recent progresses in cloud physics, processes, and associated radiative effects in China from 2016 to 2022. It mainly consists of three topics, including the recent development of cloud observation techniques, advances in understanding of cloud physical properties and processes, and quantification of cloud radiative effects (CRE). For cloud observation techniques, the launch of new-era high spatio-temporal resolution geostationary satellites makes us able to examine the diurnal variation of cloud properties, along with the cloud properties during different stages of cloud development. Correspondingly, new cloud retrieval algorithms including both physical based and machine learning methods have been developed. With more accurate and reliable aircraft observations and a longer period of satellite observations, cloud physical properties and processes have been further understood, including the spaito-temporal variations of cloud properties, the cloud droplet size distribution, the aerosol-cloud interaction processes, and so on. In addition, recent progress in aerosol effects on precipitation by affecting cloud properties and development has also been summarized, including the increase (reduction) of precipitation amount by aerosols for heavy (light) precipitation cases, the advancement of precipitation time by absorbing aerosols near surface, the delay of precipitation time by scattering aerosols near surface, and the enlarging precipitation area of tropical cyclones by aerosols. With long period radiation observations, CREs have also been quantified, including the temporal variation and spatial distribution of CREs, the various influential factors to changes of CREs, and the identification of uncertainty sources in CMIP6 model simulations of CREs. Challenges associated with cloud studies have also been proposed in this study from the perspective of observations, physical processes, and radiative effects. • Recent progresses in cloud physics and associated radiative effects in China from 2016 to 2022 are reviewed. • Geostationary satellite observations and new cloud retrieval algorithms such as machine learning were developed. • Understanding of cloud characteristics and aerosol-cloud interactions in China were advanced. • Aerosol effect on precipitation amount, area, and time were better understood. • Characteristics and influential factors of CREs are summarized. [ABSTRACT FROM AUTHOR]

This study investigates the seasonal variability of the cloud radiative effects (CREs) over Congo Basin (CB) using 15-year observations from Clouds and the Earth's Radiant Energy System (CERES) Energy Budget and Filled (EBAF) Ed4.1 level 3b dataset involving CERES and Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on board Terra and Aqua satellites. The relationships between CREs and cloud properties such as total cloud fraction (TCF), cloud top height (CTH), cloud top temperature (CTT) and cloud optical thickness (COT) are checked. An evaluation of Coupled Model Intercomparison Project (CMIP) Phase 6 in capturing the seasonal cycle of CREs as well as the magnitudes of the CREs along the seasonal cycle is also performed. This study shows a net cloud cooling effect of −8.4 W/m2 and − 43.9 W/m2 respectively at the top of the atmosphere (TOA) and at the surface, leading to a net warming effect of 35.67 W/m2 in the atmosphere. This value implies a large energy source over the Central Africa (CA) atmospheric column. The associated relationships between CREs and cloud properties show that the shortwave CRE is more sensitive to TCF and optical thickness whereas its longwave counterparts is more sensitive to CTH, CTT and COT at the TOA and in the atmosphere. All of the four CMIP6 models used in this study can capture the spatial pattern of CREs as well as their seasonal cycle but misrepresent intensity of CREs. Results also show that a better-simulated TCF considerably reduces the intensity of the annual mean underestimation in both longwave and shortwave CRE for some CMIP6 models, but not for models with overestimated shortwave CRE. • Central Africa exhibits a large energy source over its atmospheric column. • The shortwave CRE is more sensitive to total cloud fraction and optical thickness. • A better-simulated total cloud fraction reduces the underestimation in both longwave and shortwave CRE in some CMIP6 models. [ABSTRACT FROM AUTHOR]

The surface radiation environment over the Southern Ocean within the region bound by 42.8° S to 78.7° S and 62.6° E to 157.7° W is summarised for three austral summers. This is done using ship-based measurements with the combination of downwelling radiation sensors and a cloud imager. We focus on characterising the cloud radiative effect (CRE) under a variety of conditions, comparing observations in the open ocean with those in the sea ice zone. For comparison with our observed data, we obtained surface data from the European Centre for Medium-Range Weather Forecasts fifth reanalysis (ERA5). We found that the daily average cloud fraction was slightly lower in ERA5 compared with the observations (0.71 and 0.75, respectively). ERA5 also showed positive biases in the shortwave radiation effect and a negative bias in the longwave radiation effect. The observed mean surface CRE of −164 ± 100 Wm−2 was more negative than the mean surface CRE for ERA5 of −101 W m−2.

Abstract: This study examines the relationships between marine stratocumulus clouds (MSC) coupling state with the ocean surface, their precipitation rate and fractional cloud cover (CF). This was possible by developing a novel methodology for satellite retrieval of the clouds coupling state. Decks of overcast MSC were reported in previous studies to break up often as their precipitation rate increases significantly, thus reducing CF and cloud radiative effect substantially. Here we show that decks of precipitating decoupled MSC have larger CF compared to similarly precipitating coupled MSC. The difference in CF between decoupled and coupled clouds was found to increase with precipitation rate, up to nearly doubling the CF of the heaviest precipitating decoupled MSC. This suggests that decoupling is a feature related to higher cloud radiative effect in precipitating MSC. [ABSTRACT FROM AUTHOR]

Measurements of the longwave cloud radiative effect (LWCRE) at the top of the atmosphere assess the contribution of clouds to the Earth warming but do not quantify the cloud property variations that are responsible for the LWCRE variations. The CALIPSO space lidar observes directly the detailed profile of cloud, cloud opacity, and cloud cover. Here we use these observations to quantify the influence of cloud properties on the variations of the LWCRE observed between 2008 and 2015 in the tropics and at global scale. At global scale, the method proposed here gives good results except over the Southern Ocean. We find that the global LWCRE variations observed over ocean are mostly due to variations in the opaque cloud properties (82%); transparent cloud columns contributed 18%. Variation of opaque cloud cover is the first contributor to the LWCRE evolution (58%); opaque cloud temperature is the second contributor (28%). [ABSTRACT FROM AUTHOR]

This study uses 2001-2014 satellite observations and reanalyses to investigate the seasonal characteristics of Cloud Radiative Effects (CREs) and their associations with cloud fraction (CF) and precipitation over the Asian monsoon region (AMR) covering Eastern China (EC) and South Asia (SA). The CREs exhibit strong seasonal variations but show distinctly different relationships with CFs and precipitation over the two regions. For EC, the CREs is dominated by shortwave (SW) cooling, with an annual mean value of − 40 W m for net CRE, and peak in summer while the presence of extensive and opaque low-level clouds contributes to large Top-Of-Atmosphere (TOA) albedo (>0.5) in winter. For SA, a weak net CRE exists throughout the year due to in-phase compensation of SWCRE by longwave (LW) CRE associated with the frequent occurrence of high clouds. For the entire AMR, SWCRE strongly correlates with the dominant types of CFs, although the cloud vertical structure plays important role particularly in summer. The relationships between CREs and precipitation are stronger in SA than in EC, indicating the dominant effect of monsoon circulation in the former region. SWCRE over EC is only partly related to precipitation and shows distinctive regional variations. Further studies need to pay more attention to vertical distributions of cloud micro- and macro-physical properties, and associated precipitation systems over the AMR. [ABSTRACT FROM AUTHOR]

Processes of plant growth are affected by solar radiation reaching the surface, which is regulated by atmospheric components such as aerosols and clouds. However, there are still large uncertainties in evaluating the impact of aerosol radiative effects (ARE) and cloud radiative effects (CRE) on ecosystems. This study estimated the ARE and CRE on vegetation productivity from 2001 to 2020 over the Northeast Qinghai-Tibet Plateau (QTP) based on MODIS satellite data coupled with the validated Radiative Transfer model (RTM) libRadtran and CASA (Carnegie-Ames-Stanford Approach)model. The results showed that both ARE and CRE have restrained vegetation growth in the last 20 years. The net primary productivity (NPP) of vegetation attenuation by ARE was strongest in summer with an increase of temperature and humidity which caused enhanced air particle transformation and hygroscopic growth, followed by spring and autumn, which were extremely affected by dust, and NPP attenuation by ARE was weakest in winter, accounting for 5.2% of the annual NPP. CRE plays an attenuating role on NPP with increasing cloudiness. The ARE reduced NPP by 18.8 g C/m2/yr, and CRE reduced NPP by 406.9 g C/m2/yr. NPP attenuation by CRE was more than ten times that of NPP attenuation by ARE, which indicated that the CRE has a much stronger weakening of NPP than ARE. The area where the trend of NPP at all-sky conditions increases/decreases had a good match with the areas where the trend of NPP by CRE increases/decreases with R2 being 0.89, indicating that CRE plays a dominant role in attenuating NPP. The increase in NPP is mainly attributed to the decrease in NPP attenuation by CRE over the past two decades. The study results could help to comprehensively understand the ARE and CRE on the terrestrial carbon cycle, and to further access and analyze vegetation ecosystem conditions. • The radiative effects of aerosol and cloud on NPP over Northeast QTP were evaluated. • NPP attenuation by CRE was more than ten times that by ARE. • CRE plays a dominant role in the increase in NPP in the past two decades. [ABSTRACT FROM AUTHOR]

Active cloud observations from A-Train's CloudSat and CALIPSO satellites offer new opportunities to examine the vertical structure of hydrometeor layers. We use the 2B-CLDCLASS-LIDAR merged CloudSat-CALIPSO product to examine global aspects of hydrometeor vertical stratification. We group the data into major cloud vertical structure (CVS) classes based on our interpretation of how clouds in three standard atmospheric layers overlap and provide their global frequency of occurrence. The two most frequent CVS classes are single-layer (per our definition) low and high clouds that represent ~53% of cloudy skies, followed by high clouds overlying low clouds, and vertically extensive clouds that occupy near-contiguously a large portion of the troposphere. The prevalence of these configurations changes seasonally and geographically, between daytime and nighttime, and between continents and oceans. The radiative effects of the CVS classes reveal the major radiative warmers and coolers from the perspective of the planet as a whole, the surface, and the atmosphere. Single-layer low clouds dominate planetary and atmospheric cooling and thermal infrared surface warming. We also investigate the consistency between passive and active views of clouds by providing the CVS breakdowns of Moderate Resolution Imaging Spectroradiometer cloud regimes for spatiotemporally coincident MODIS-Aqua (also on the A-Train) and CloudSat-CALIPSO daytime observations. When the analysis is expanded for a more in-depth look at the most heterogeneous of the MODIS cloud regimes, it ultimately confirms previous interpretations of their makeup that did not have the benefit of collocated active observations. [ABSTRACT FROM AUTHOR]