Search

Not only total solar irradiance (TSI) but also spectral solar irradiance (SSI) matter for our climate. Different surfaces can have different reflectivity for the visible (VIS) and near-infrared (NIR). The recent NASA Total and Spectral Solar Irradiance Sensor (TSIS-1) mission has provided more accurate SSI observations than before. The TSI observed by TSIS-1 differs from the counterpart used by climate models by no more than 1 W m−2. However, the SSI difference in a given VIS (e.g., 0.44–0.63 μm) and NIR (e.g., 0.78–1.24 μm) band can be as large as 4 W m−2 with opposite signs. Using the NCAR CESM2, we study to what extent such different VIS and NIR SSI partitions can affect the simulated climate. Two sets of simulations with identical TSI are carried out, one with SSI partitioning as observed by the TSIS-1 mission and the other with what has been used in the current climate models. Due to different VIS-NIR spectral reflectance contrasts between icy (or snowy) surfaces and open water, the simulation with more SSI in the VIS has less solar absorption by the high-latitude surfaces, ending up with colder polar surface temperature and larger sea ice coverage. The difference is more prominent over the Antarctic than over the Arctic. Our results suggest that, even for the identical TSI, the surface albedo feedback can be triggered by different SSI partition between the VIS and NIR. The results underscore the importance of continuously monitoring SSI and the use of correct SSI in climate simulations. [ABSTRACT FROM AUTHOR]

In this study, the radiation scheme BCC-RAD (Beijing Climate Center RADiative transfer model) developed for global climate models is implemented into the Global–Regional Integrated SysTem (GRIST) model as an alternative to the default RRTMG (general circulation model (GCM) version of the Rapid Radiative Transfer Model) scheme. Its impact on the simulated climate is comprehensively evaluated under different physics parametrization packages, in comparison with both the CERES (partly from ERA5 reanalysis) observations and multi-model results from CMIP6. The results indicate that under the default physics parameterization package of GRIST (PhysC), BCC-RAD improved the simulated global mean cloud cover by ~3% and the clear-sky outgoing longwave radiation by ~5.6 W/m2. Upon the inclusion of the PhysCN parameterization package, BCC-RAD exhibited further improvement in simulated cloud cover and radiative forcing (particularly longwave radiative forcing, the bias of which decreases from −9.2 W/m2 to −1.8 W/m2), leading it to be closer to observations than RRTMG. Additionally, BCC-RAD improved the simulation of atmospheric temperature and hence notably diminished the apparent overestimation of atmospheric humidity seen in RRTMG. This study demonstrates the advantages of BCC-RAD over RRTMG in certain aspects of the GRIST-simulated climate, verifying its capability for the climate-oriented configuration of GRIST. [ABSTRACT FROM AUTHOR]

Global climate models (GCMs) have been found to share the common too-frequent bias in the warm rain formation process. In this study, five different autoconversion schemes are incorporated into a single GCM, to systematically evaluate the warm rain formation processes in comparison with satellite observations and investigate their effects on the aerosol indirect effect (AIE). It is found that some schemes generate warm rain less efficiently under polluted conditions in the manner closer to satellite observations, while the others generate warm rain too frequently. Large differences in AIE are found among these schemes. It is remarkable that the schemes with more observation-like warm rain formation processes exhibit larger AIEs that far exceed the uncertainty range reported in IPCC AR5, to an extent that can cancel much of the warming trend in the past century, whereas schemes with too-frequent rain formations yield AIEs that are well bounded by the reported range. The power-law dependence of the autoconversion rate on the cloud droplet number concentration β is found to affect substantially the susceptibility of rain formation to aerosols: the more negative β is, the more difficult it is for rain to be triggered in polluted clouds, leading to larger AIE through substantial contributions from the wet scavenging feedback. The appropriate use of a droplet size threshold can mitigate the effect of a less negative β. The role of the warm rain formation process on AIE in this particular model has broad implications for others that share the too-frequent rain-formation bias. [ABSTRACT FROM AUTHOR]

Vertical decorrelation length ( L cf ) as used to determine overlap of cloudy layers in GCMs was obtained from CloudSat/CALIPSO measurements, made between 2007 and 2010, and analyzed in terms of monthly means. Global distributions of L cf were produced for several cross-sectional lengths. Results show that: L cf over the tropical convective regions typically exceeds 2 km and shift meridionally with season; the smallest L cf (< 1 km) tends to occur in regions dominated by marine stratiform clouds; L cf for mid-to-high latitude continents of the Northern Hemisphere (NH) ranges from 5–6 km during winter to 2–3 km during summer; and there are marked differences between continental and oceanic values of L cf in the mid-latitudes of the NH. These monthly-gridded, observationally-based values of L cf data were then used by the Monte Carlo Independent Column Approximation (McICA) radiation routines within the Beijing Climate Center's GCM (BCC_AGCM2.0.1). Additionally, the GCM was run with two other descriptions of L cf : one varied with latitude only, and the other was simply 2 km everywhere all the time. It is shown that using the observationally-based L cf in the GCM led to local and seasonal changes in total cloud fraction and shortwave (longwave) cloud radiative effects that serve mostly to reduce model biases. This indicates that usage of L cf that vary according to location and time has the potential to improve climate simulations. [ABSTRACT FROM AUTHOR]

Cloud albedo is expected to influence cloud radiative forcing in addition to cloud fraction, and inadequate description of the cloud overlapping effects on the cloud fraction may influence the simulated cloud fraction, and thus the relative cloud radiative forcing (RCRF) and cloud albedo. In this study, we first present a new formula by extending that presented previously to consider multilayer clouds directly in the relationship between cloud albedo, cloud fraction, and RCRF, and then quantitatively evaluate the effects of different cloud vertical overlapping structures, represented by the decorrelation length scales (Lcf), on the simulated cloud albedos. We use the BCC_AGCM2.0_CUACE/Aero model with simultaneous validation by observations from the Clouds and the Earth's Radiation Energy System (CERES) satellite. When Lcf < 4 km (i.e., the cloud overlap is closer to the random overlap), the simulated cloud albedos are generally in good agreement with the satellite-based albedos for December–February and June–August; when Lcf ≥ 4 km (i.e., the cloud vertical overlap is closer to the maximum overlap), the difference between simulated and observed cloud albedos became larger, due mainly to significant differences in cloud fractions and RCRF. Further quantitative analysis shows that the relative Euclidean distance, which represents the degree of overall model–observation disagreement, increases with the Lcf for all three variables (cloud albedo, cloud fraction, and RCRF), indicating the importance of cloud vertical overlapping in determining the accuracy of the calculated cloud albedo for multilayer clouds. Significance Statement: The purpose of this study is presenting a new formula to consider multilayer clouds directly in the relationship between cloud albedo, cloud fraction, and relative cloud radiative forcing (RCRF). This is important because the effects of different cloud vertical overlapping structures, represented by the decorrelation length scales (Lcf), can affect the simulated cloud albedos. Our results provide a guide on the importance of cloud vertical overlapping in determining the accuracy of the calculated cloud albedo for multilayer clouds. [ABSTRACT FROM AUTHOR]

Many global climate models have been found to generate warm rain too frequently. This study, with a particular global climate model, found that the problem can be mitigated via altering the autoconversion process so as to inhibit rain formation under conditions of a large cloud number concentration and small droplet sizes. However, this improvement was found to cause an overly large aerosol indirect effect. This dichotomy between the constraint on warm‐rain formation process and the energy‐budget requirement on aerosol indirect effect was found to result from a pronounced cloud‐water response to aerosol perturbations, which is amplified through the wet scavenging feedback to an extent depending on precipitation‐formation parameterization. Thus, critical compensating errors exist between warm‐rain formation and other key processes, and better constraint on these processes, particularly wet scavenging, is required to mitigate the dichotomy. The results have broad implication for models that suffer from the aforementioned too‐frequent warm‐rain formation bias. Plain Language Summary: Climate scientists rely on numerical climate models to project temperature changes in the coming decades. The credibility of the projections is argued to arise from the fact that models are able to reproduce well the temperature trend in the past century. However, success in reproducing the past does not necessarily mean credible projection for the future, because the former may be a result of compensating biases in the models, which potentially misrepresent the relationship between changes to the energy balance and aerosols/clouds. In this study, compensating biases were found to exist between rain formation and other processes in a model capable of simulating aerosol effects. Specifically, this model tends to generate rain too frequently against satellite observations, whereas satellite‐based improvements with respect to the rain process yield an unrealistically strong aerosol indirect effect that can substantially cool the surface. This means that dual efforts are required to derive trustworthy projections of future climate changes: on the one hand, the rain‐formation process should be represented realistically in accordance with observations, while on the other hand, errors in the interaction between rain and aerosol/cloud should be mitigated. Key Points: Formulation of autoconversion was found to determine the manner of warm‐rain formation and the occurrence of nonprecipitating cloudsProcess‐based constraint on warm rain was found to cause overly negative aerosol indirect effect in a GCMThe overestimation of the AIE stems from a pronounced cloud‐water response to aerosol that is amplified via the rain‐scavenging interplay [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Characteristics of cloud overlap over Eastern Asia are analyzed using a three-year dataset (2007-2009) from the cloud observing satellite CloudSat. Decorrelation depth L* is retrieved, which represents cloud overlap characteristics in the simulation of cloud-radiation processes in global climate models. Results show that values of L* in six study regions are generally within the range 0-3 km. By categorizing L* according to cloud amount in subregions, peak L* appears near subregions with cloud amount between 0.6 and 0.8. Average L* is 2.5 km. L* at higher altitudes is generally larger than at lower latitudes. Seasonal variations of L* are also clearly demonstrated. The sensitivity of cloud radiative forcing (CRF) to L* in Community Atmosphere Model 3.0 of the National Center for Atmospheric Research (CAM3/NCAR) is analyzed. The result shows that L* can have a big impact on simulation of CRF, especially in major monsoon regions and the Mid-Eastern Pacific, where the difference in CRF can reach 40-50 W m. Therefore, accurate parameterization of cloud vertical overlap structure is important to CRF simulation and its feedback to climate. [ABSTRACT FROM AUTHOR]

Abstract: The optical properties of spherical and non-spherical dust aerosols are calculated using the Lorenz–Mie theory and the combination of T-matrix method and an improved geometric optics method. The resulting optical properties are then applied in an interactive system that coupled a general circulation model with an aerosol model to quantitatively analyze the effect of non-spherical dust aerosol on its direct radiative forcing (DRF). Our results show that the maximum difference in dust instantaneous radiative forcing (IRF) between spherical and non-spherical particles is 0.27Wm−2 at the top of the atmosphere (TOA) and appears over the Sahara Desert due to enhanced absorption of solar radiation by non-spherical dust. The global annual means of shortwave (longwave) IRFs due to spherical and non-spherical dust aerosols at the TOA for all sky are −0.62 (0.074) Wm−2 and −0.61 (0.073) Wm−2, respectively, and the corresponding values for clear sky are −1.16 (0.092) Wm−2 and −1.14 (0.093) Wm−2, which indicates that the non-spherical effect of dust has almost no effect on their global annual mean IRFs. However, non-spherical dust displays more evident influences than above on its atmospheric- and land-temperature adjusted radiative forcing (AF) at the TOA over the Saharan Desert, West Asia, and northern China, with an approximate maximum increase of 3.0 and decrease of 0.5Wm−2. The global annual means of shortwave (longwave) AFs due to spherical and non-spherical dust aerosols are −0.55 (0.052) Wm−2 and −0.48 (0.049) Wm−2 at the TOA for all sky, respectively, and the corresponding values for clear sky are −1.07 (0.066) Wm−2 and −0.95 (0.062) Wm−2. All AFs of dust become much weaker than their corresponding IRFs. The absolute values of annual mean AF for non-spherical dust are approximately 13% (11.2%) and 6% (6%) less than those of spherical dust for the shortwave and longwave for all sky (clear sky), respectively. The results indicate that the non-spherical effect of dust can reduce their AFs more obviously than do their IRFs. [Copyright &y& Elsevier]

Carbon dioxide (CO 2) geological storage (CGS) can help realize the plan of "Carbon Neutrality". Injection capacity and storage safety are crucial factors in evaluating CO 2 storage efficiency. Deep saline aquifers are major sites for CGS. This study focused on evaluating the CO 2 injection amount, migration safety and leakage risk. A three-dimensional (3D) model of the Shenhua CO 2 capture and storage (CCS) project in the Ordos Basin, China, was established to discuss the impact of injection pressure (1.3P (equal to 1.3 times the top reservoir formation hydrostatic pressure), 1.4P, and 1.5P) and formation dip angle (0°, 5°, 10°, 15°) with fault on the total CO 2 injection and migration safety. Twelve schemes were designed for simulation. Based on the results, faulting provided a pathway for CO 2 leakage, posing a threat to CO 2 storage safety. Injection pressure and formation dip angle had significant effects on injectivity and migration during CO 2 storage. The influence of the injection pressure on the CO 2 injection amount was more evident than that of the dip angle, though formation dip angle had a significant impact on the CO 2 migration during storage. Increasing the injection pressure and formation dip angle increased the gas and dissolved-phase CO 2 migration and decreased the CO 2 leakage time and storage safety. The CO 2 leakage through the fault occurred after 160, 110 and 80 years in a 15° sloping formation with 1.3P, 1.4P, and 1.5P, respectively. The CO 2 injection amount was the largest for the 0° formation with 1.5P. These results provide fundamental information for CO 2 storage safety and capacity, suggesting that un-faulted reservoirs with smaller dip angles should be selected for CGS projects; however, larger injection pressures can result in greater injection amounts, decreasing the migration safety of CO 2 during storage. • A suite of 3D models with faulting and dip angle and injection pressure were built. • The law of CO 2 plume migration and storage had been revealed. • Larger dip angle is not conducive to CO 2 storage. • Higher injection pressure leads to increased injection amount and reduced safety. • The results will help to inform site selection for future CCS projects. [ABSTRACT FROM AUTHOR]

A review of the progression of cloud physics from a subdiscipline of meteorology into the global science it is today is described. The discussion briefly touches on the important post‐war contributions of three key individuals who were instrumental in developing cloud physics into a global science. These contributions came on the heels of the post‐war weather modification efforts that influenced much of the early development of cloud physics. The review is centred on the properties of warm clouds primarily to limit the scope of the article and the connection between the early contributions to cloud physics and the current vexing problem of aerosol effects on cloud albedo is underlined. Progress toward estimating cloud properties from space and insights on warm cloud processes are described. Measurements of selected cloud properties, such as cloud liquid water path are now mature enough that multi‐decadal time series of these properties exist and this climatology is used to compare to analogous low‐cloud properties taken from global climate models. The too‐wet (and thus too bright) and the too‐dreary biases of models are called out underscoring the challenges we still face in representing warm clouds in Earth system models. We also provide strategies for using observations to constrain the indirect radiative forcing of the climate system. [ABSTRACT FROM AUTHOR]

The Cloud Feedback Model Intercomparison Project Observational Simulator Package (COSP) is used to diagnose model performance and physical processes via an apple-to-apple comparison to satellite measurements. Although the COSP provides useful information about clouds and their climatic impact, outputs that have a subcolumn dimension require large amounts of data. This can cause a bottleneck when conducting sets of sensitivity experiments or multiple model intercomparisons. Here, we incorporate two diagnostics for warm rain microphysical processes into the latest version of the simulator (COSP2). The first one is the occurrence frequency of warm rain regimes (i.e., non-precipitating, drizzling, and precipitating) classified according to CloudSat radar reflectivity, putting the warm rain process diagnostics into the context of the geographical distributions of precipitation. The second diagnostic is the probability density function of radar reflectivity profiles normalized by the in-cloud optical depth, the so-called contoured frequency by optical depth diagram (CFODD), which illustrates how the warm rain processes occur in the vertical dimension using statistics constructed from CloudSat and MODIS simulators. The new diagnostics are designed to produce statistics online along with subcolumn information during the COSP execution, eliminating the need to output subcolumn variables. Users can also readily conduct regional analysis tailored to their particular research interest (e.g., land–ocean differences) using an auxiliary post-process package after the COSP calculation. The inline diagnostics are applied to the MIROC6 general circulation model (GCM) to demonstrate how known biases common among multiple GCMs relative to satellite observations are revealed. The inline multi-sensor diagnostics are intended to serve as a tool that facilitates process-oriented model evaluations in a manner that reduces the burden on modelers for their diagnostics effort. [ABSTRACT FROM AUTHOR]

Realistic climate and weather prediction models are necessary to produce confidence in projections of future climate over many decades and predictions for days to seasons. These models must be physically justified and validated for multiple weather and climate processes. A key opportunity to accelerate model improvement is greater incorporation of process-oriented diagnostics (PODs) into standard packages that can be applied during the model development process, allowing the application of diagnostics to be repeatable across multiple model versions and used as a benchmark for model improvement. A POD characterizes a specific physical process or emergent behavior that is related to the ability to simulate an observed phenomenon. This paper describes the outcomes of activities by the Model Diagnostics Task Force (MDTF) under the NOAA Climate Program Office (CPO) Modeling, Analysis, Predictions and Projections (MAPP) program to promote development of PODs and their application to climate and weather prediction models. MDTF and modeling center perspectives on the need for expanded process-oriented diagnosis of models are presented. Multiple PODs developed by the MDTF are summarized, and an open-source software framework developed by the MDTF to aid application of PODs to centers' model development is presented in the context of other relevant community activities. The paper closes by discussing paths forward for the MDTF effort and for community process-oriented diagnosis. [ABSTRACT FROM AUTHOR]

The comprehensive effects of anthropogenic aerosols (sulfate, black carbon, and organic carbon) on terrestrial aridity were simulated using an aerosol-climate coupled model system. The results showed that the increase in total anthropogenic aerosols in the atmosphere from 1850 to 2010 had caused global land annual mean precipitation to decrease by about 0.19 (0.18, 0.21) mm day−1, where the uncertainty range of the change (minimum, maximum) is given in parentheses following the mean change, and reference evapotranspiration ET0 (representing evapotranspiration ability) to decrease by about 0.33 (0.31, 0.35) mm day−1. The increase in anthropogenic aerosols in the atmosphere from 1850 to 2010 had caused land annual mean terrestrial aridity to decrease by about 3.0% (2.7%, 3.6%). The areal extent of global total arid and semiarid areas had reduced due to the increase in total anthropogenic aerosols in the atmosphere from preindustrial times. However, it was found that the increase in anthropogenic aerosols in the atmosphere had enhanced the terrestrial aridity and thus resulted in an expansion of arid and semiarid areas over East and South Asia. The projected decrease in anthropogenic aerosols in the atmosphere from 2010 to 2100 will increase global land annual mean precipitation by about 0.15 (0.13, 0.16) mm day−1 and ET0 by about 0.26 (0.25, 0.28) mm day−1, thereby producing a net increase in terrestrial aridity of about 2.8% (2.1%, 3.6%) and an expansion of global total arid and semiarid areas. [ABSTRACT FROM AUTHOR]

The Gaussian–Legendre, Gaussian–Lobatto, Gaussian–Chebyshev and Gaussian quadrature (GQ) with different moment powers have been investigated by applying them into the four-stream solar and infrared radiative transfer algorithms. For solar radiative transfer, the Gaussian–Chebyshev and GQ with moment power m =0 show relatively accurate results compared to other types of 2GQ in a single-layer scattering medium. In a real atmospheric profile including gaseous transmission, Gaussian–Chebyshev and GQ with moment power m =0 are comparable in accuracy for cloud heating rate. GQ with moment power m =0 produces more accurate results in the upward flux at the top of the atmosphere, while Gaussian–Chebyshev produces more accurate results in the downward flux at the surface. These results have been confirmed in evaluations by using satellite observation data. For infrared radiative transfer, the GQ with moment powers m = 0 , 2 , 4 show relatively accurate results in effective emissivity for a single-layer scattering medium. In a real atmospheric profile, the GQ with moment powers m =0 and m =2 show superior accuracy in heating rate and flux. In addition, the evaluations using satellite observation data also show that the accuracy of GQ with moment powers m =0 and m =2 is comparable. Both the schemes are the best candidates for the four-stream radiation algorithms. [ABSTRACT FROM AUTHOR]

Global radiation over China decreased between the 1960s and 1990, since when it has remained stable. As the total cloud cover has continued to decrease since the 1960s, variations in aerosols were suggested in previous studies to be the primary cause for variations in global radiation over China. However, the effect of aerosols on global radiation on a decadal scale has not been physically quantified over China. In this study, aerosol optical depth (AOD) data since 1980 are estimated by combining horizontal visibility data at stations in China and AOD observed by the moderate resolution imaging spectroradiometer (MODIS). It is found that the AOD exhibits decadal changes, with two decreasing periods (before the end of 1980s and after 2006) and one increasing period (from 1990 to 2006). With the derived AOD, a clear-sky model is then applied to quantify the role of aerosols in the variations in global radiation over China. The results show that aerosol direct effect cannot fully explain the decadal variations in the global radiation over China between 1980 and 2010, though it has a considerable effect on global radiation climatology. There are significant differences between the trends of clear-sky global radiation impacted by aerosols and those of all-sky global radiation impacted by aerosols and clouds, and the correlation coefficient for the comparison is very low. Therefore, the variations in all-sky global radiation over China are likely to be due to changes in cloud properties and to interactions between clouds and aerosols. [ABSTRACT FROM AUTHOR]

Large uncertainties remain in the estimation of aerosol direct radiative effect (DRE) and forcing (DRF). In this work, using an aerosol-climate model with two- and four-stream radiation schemes, we show that the radiative transfer algorithms contribute to the uncertainties. Aerosol shortwave DREs and heating rate are underestimated significantly by the two-stream algorithm. For present-day conditions, the four-stream algorithms are found to enhance global annualmean aerosol shortwave DREs by more than 8% (14%) at the top of the atmosphere (TOA), 15% (18%) in the atmosphere, and 12% (15%) at the surface for all-sky (clear-sky) case. The regional-averaged relative differences in aerosol shortwave DREs between the two- and four-stream algorithms increase as latitude increases, exceeding 25% at the TOA and 30% at the surface in the high latitudes of the Southern Hemisphere. The DRE differences due to the four-stream algorithms are negative, except for the Arctic, Tibetan Plateau, Arabia, and Sahara, at the TOA, are positive in the atmosphere, and are negative at the surface, with the maximum exceeding 4.0Wm-2. Increases in aerosol shortwave heating rates due to the four-stream algorithms are generally more than 10% and may even exceed 100%. Our results also show that the two-stream algorithm underestimates the DRFs due to anthropogenic aerosols. Significant underestimation appears in the middle latitudes of the Northern Hemisphere, with the maximum being close to the quantity of 0.6Wm-2 for clear-sky case. This study indicates that a multi-stream radiative transfer algorithm is necessary to reduce the uncertainties of aerosol DREs and DRFs estimated by global climate models. [ABSTRACT FROM AUTHOR]