Water Vapor and Cloud Radiative Forcings over the Pacific Ocean Simulated by the LASG/IAP AGCM:Sensitivity to Convection Schemes

Characteristics of the total clear-sky greenhouse effect （GA） and cloud radiative forcings （CRFs）, along with the radiative-related water vapor and cloud properties simulated by the Spectral Atmospheric Model developed by LASGIAP （SAMIL） are evaluated. Impacts of the convection scheme on the simulation of CRFs are discussed by using two AMIP （Atmospheric Model Inter-comparison Project） type simulations employing different convection schemes： the new Zhang-McFarlane （NZH） and Tiedtke （TDK） convection schemes. It shows that both the climatological GA and its response to El Nio warming are simulated well, both in terms of spatial pattern and magnitude. The impact of the convection scheme on GA is not significant. The climatological longwave CRF （LWCRF） and its response to El Nio warming are simulated well, but with a prominently weaker magnitude. The simulation of the climatology （response） of LWCRF in the NZH （TDK） run is slightly more realistic than in the TDK （NZH） simulation, indicating significant impacts of the convection scheme. The shortwave CRF （SWCRF） shows large biases in both spatial pattern and magnitude, and the results from the TDK run are better than those from the NZH run. A spuriously excessive negative climatological SWCRF over the southeastern Pacific and an insufficient response of SWCRF to El Nio warming over the tropical Pacific are seen in the NZH run. These two biases are alleviated in the TDK run, since it produces vigorous convection, which is related to the low threshold for convection to take place. Also, impacts of the convection scheme on the cloud profile are discussed.

Shortwave Cloud Radiative Forcing on Major Stratus Cloud Regions in AMIP-type Simulations of CMIP3 and CMIP5 Models

Cloud and its radiative effects are major sources of uncertainty that lead to simulation discrepancies in climate models. In this study, shortwave cloud radiative forcing （SWCF） over major stratus regions is evaluated for Atmospheric Models Intercomparison Project （AMIP）-type simulations of models involved in the third and fifth phases of the Coupled Models Intercomparison Project （CMIP3 and CMIP5）. Over stratus regions, large deviations in both climatological mean and seasonal cycle of SWCF are found among the models. An ambient field sorted by dynamic （vertical motion） and thermodynamic （inversion strength or stability） regimes is constructed and used to measure the response of SWCF to large-scale controls. In marine boundary layer regions, despite both CMIP3 and CMIP5 models being able to capture well the center and range of occurrence frequency for the ambient field, most of the models fail to simulate the dependence of SWCF on boundary layer inversion and the insensitivity of SWCF to vertical motion. For eastern China, there are large differences even in the simulated ambient fields. Moreover, almost no model can reproduce intense SWCF in rising motion and high stability regimes. It is also found that models with a finer grid resolution have no evident superiority than their lower resolution versions. The uncertainties relating to SWCF in state-of-the-art models may limit their performance in IPCC experiments.

Cloud Radiative Forcing in Asian Monsoon Region Simulated by IPCC AR4 AMIP Models

This study examines cloud radiative forcing （CRF） in the Asian monsoon region （0° 50°N, 60° 150°E） simulated by Intergovernmental Panel on Climate Change （IPCC） Fourth Assessment Report （AR4） AMIP models. During boreal winter, no model realistically reproduces the larger long-wave cloud radiative forcing （LWCF） over the Tibet Plateau （TP） and only a couple of models reasonably capture the larger short-wave CRF （SWCF） to the east of the TP. During boreal summer, there are larger biases for central location and intensity of simulated CRF in active convective regions. The CRF biases are closely related to the rainfall biases in the models. Quantitative analysis further indicates that the correlation between simulated CRF and observations are not high, and that the biases and diversity in SWCF are larger than that in LWCF. The annual cycle of simulated CRF over East Asia （0°-50°N, 100°-145°E） is also examined. Though many models capture the basic annual cycle in tropics, strong LWCF and SWCF to the east of the TP beginning in early spring are underestimated by most models. As a whole, GFDL-CM2.1, MPI-ECHAM5, UKMO-HadGAM1, and MIROC3.2 （medres） perform well for CRF simulation in the Asian monsoon region, and the multi-model ensemble （MME） has improved results over the individual simulations. It is suggested that strengthening the physical parameterizations involved over the TP, and improving cumulus convection processes and model experiment design are crucial to CRF simulation in the Asian monsoon region.

The Significant Role of Radiosonde-measured Cloud-base Height in the Estimation of Cloud Radiative Forcing

The satellite-based quantification of cloud radiative forcing remains poorly understood,due largely to the limitation or uncertainties in characterizing cloud-base height(CBH).Here,we use the CBH data from radiosonde measurements over China in combination with the collocated cloud-top height(CTH) and cloud properties from MODIS/Aqua to quantify the impact of CBH on shortwave cloud radiative forcing(SWCRF).The climatological mean SWCRF at the surface(SWCRFSUR),at the top of the atmosphere(SWCRFTOA),and in the atmosphere(SWCRFATM) are estimated to be-97.14,-84.35,and 12.79 W m^(-2),respectively for the summers spanning 2010 to 2018 over China.To illustrate the role of the cloud base,we assume four scenarios according to vertical profile patterns of cloud optical depth(COD).Using the CTH and cloud properties from MODIS alone results in large uncertainties for the estimation of SWCRFATM,compared with those under scenarios that consider the CBH.Furthermore,the biases of the CERES estimation of SWCRFATM tend to increase in the presence of thick clouds with low CBH.Additionally,the discrepancy of SWCRFATM relative to that calculated without consideration of CBH varies according to the vertical profile of COD.When a uniform COD vertical profile is assumed,the largest SWCRF discrepancies occur during the early morning or late afternoon.By comparison,the two-point COD vertical distribution assumption has the largest uncertainties occurring at noon when the solar irradiation peaks.These findings justify the urgent need to consider the cloud vertical structures when calculating the SWCRF which is otherwise neglected.

LASG Global AGCM with a Two-moment Cloud Microphysics Scheme:Energy Balance and Cloud Radiative Forcing Characteristics

Cloud dominates influence factors of atmospheric radiation, while aerosol–cloud interactions are of vital importance in its spatiotemporal distribution. In this study, a two-moment(mass and number) cloud microphysics scheme, which significantly improved the treatment of the coupled processes of aerosols and clouds, was incorporated into version 1.1 of the IAP/LASG global Finite-volume Atmospheric Model(FAMIL1.1). For illustrative purposes, the characteristics of the energy balance and cloud radiative forcing(CRF) in an AMIP-type simulation with prescribed aerosols were compared with those in observational/reanalysis data. Even within the constraints of the prescribed aerosol mass, the model simulated global mean energy balance at the top of the atmosphere(TOA) and at the Earth’s surface, as well as their seasonal variation, are in good agreement with the observational data. The maximum deviation terms lie in the surface downwelling longwave radiation and surface latent heat flux, which are 3.5 W m-2(1%) and 3 W m-2(3.5%), individually. The spatial correlations of the annual TOA net radiation flux and the net CRF between simulation and observation were around 0.97 and 0.90, respectively. A major weakness is that FAMIL1.1 predicts more liquid water content and less ice water content over most oceans. Detailed comparisons are presented for a number of regions, with a focus on the Asian monsoon region(AMR). The results indicate that FAMIL1.1 well reproduces the summer–winter contrast for both the geographical distribution of the longwave CRF and shortwave CRF over the AMR. Finally, the model bias and possible solutions, as well as further works to develop FAMIL1.1 are discussed.

Impact of Arctic Oscillation on cloud radiative forcing and September sea ice retreat

The Arctic Oscillation(AO)has important effects on the sea ice change in terms of the dynamic and thermodynamic processes.However,while the dynamic processes of AO have been widely explored,the thermodynamic processes of AO need to be further discussed.In this paper,we use the fifth state-of-the-art reanalysis at European Centre for Medium-Range Weather Forecasts(ERA5)from 1979 to 2020 to investigate the relationship between AO and the surface springtime longwave(LW)cloud radiative forcing(CRF),summertime shortwave(SW)CRF in the Arctic region(65°-90°N).In addition,the contribution of CRF induced by AO to the sea ice change is also discussed.Results indicate that the positive(negative)anomalies of springtime LW CRF and summertime SW CRF are generally detected over the Arctic Ocean during the enhanced positive(negative)AO phase in spring and summer,respectively.Meanwhile,while the LW(SW)CRF generally has a positive correlation with AO index(AOI)in spring(summer)over the entire Arctic Ocean,this correlation is statistically significant over 70°-85°N and 120°W-90°E(i.e.,region of interest(ROI))in both seasons.Moreover,the response of CRF to the atmospheric conditions varies in spring and summer.We also find that the positive springtime(summertime)AOI tends to decrease(increase)the sea ice in September,and this phenomenon is especially prominent over the ROI.The sensitivity study among sea ice extent,CRF and AOI further reveals that decreases(increases)in September sea ice over the ROI are partly attributed to the springtime LW(summertime SW)CRF during the positive AOI.The present study provides a new pattern of AO affecting sea ice change via cloud radiative effects,which might benefit the sea ice forecast improvement.

Cloud-Aerosol-Radiation (CAR) Ensemble Modeling System: Overall Accuracy and Efficiency

The Cloud Aerosol- Radiation （CAR） ensemble modeling system has recently been built to better un- derstand cloud/aerosol/radiation processes and determine the uncertainties caused by different treatments of cloud/aerosol/radiation in climate models. The CAR system comprises a large scheme collection of cloud, aerosol, and radiation processes available in the literature, including those commonly used by the world＇s leading GCMs. In this study, detailed analyses of the overall accuracy and efficiency of the CAR system were performed. Despite the different observations used, the overall accuracies of the CAR ensemble means were found to be very good for both shortwave （SW） and longwave （LW） radiation calculations. Taking tile percentage errors for July 2004 compared to ISCCP （International Satellite Cloud Climatology Project） data over （60~N, 60~S） as an example, even among the 448 CAR members selected here, those errors of the CAR ensemble means were only about -0.67% （-0.6 W m-2） and -0.82% （-2.0 W m-2） for SW and LW upward fluxes at the top of atmosphere, and 0.06% （0.1 W m-2） and -2.12% （-7.8 W m 2） for SW and LW downward fluxes at the surface, respectively. Furthermore, model SW frequency distributions in July 2004 covered the observational ranges entirely, with ensemble means located in the middle of the ranges. Moreover, it was found that the accuracy of radiative transfer calculations can be significantly enhanced by＂ using certain combinations of cloud schemes for the cloud cover fraction, particle effective size, water path, and optical properties, along with better explicit treatments for unresolved cloud structures.

Intercomparison of Surface Radiative Fluxes in the Arctic Ocean

最近的卫星数据分析在北极海洋提供了与表面精力预算相关的改进数据集合。在这份报纸，在从表面放射预算(SRB3.0 ) 和国际卫星获得的北极海洋的表面放射性质在 19842007 期间遮蔽气候学工程(ISCCP-FD ) 被分析并且比较。我们的分析建议这些数据集在盆宽的平均季节的周期和表面反照率的空间分发显示出令人鼓舞的同意；捕捞表面短波和从所有方向的放射的流动；并且短波， longwave，和从所有方向的云放射的 forcings。然而，系统的大差异为在在大小 of23 W m2 的二个数据集合之间的放射的流动，它是首先在表面温度归因于重要差别的网络表面 longwave 被检测，特别地从 4 月到 6 月。而且，在表面短波的最大的差别和在二个数据之间的放射的 forcings 设置的从所有方向的云在在 30 W m 2 的大小的早 6 月是明显的。

Cloud Radiative Forcing Induced by Layered Clouds and Associated Impact on the Atmospheric Heating Rate

A quantitative analysis of cloud fraction, cloud radiative forcing, and cloud radiative heating rate （CRH） of the single-layered cloud （SLC） and the multi-layered cloud （MLC）, and their differences is presented, based on the 2B-CLDCLASS-LIDAR and 2B-FLXHR-LIDAR products on the global scale. The CRH at a given atmospheric level is defined as the cloudy minus clear-sky radiative heating rate. The statistical results show that the globally averaged cloud fraction of the MLC （24.9%）, which is primarily prevalent in equatorial regions, is smaller than that of the SLC （46.6%）. The globally averaged net radiative forcings （NET CRFs） induced by the SLC （MLC） at the top and bottom of the atmosphere （TOA and BOA） and in the atmosphere （ATM） are -60.8 （40.9）, 67.5 （49.6）, and 6.6 （8.7） W m-2, respectively, where the MLC contributes approximately 40.2%, 42.4%, and 57% to the NET CRF at the TOA, BOA, and in the ATM, respectively. The MLC exhibits distinct differences to the SLC in terms of CRH. The shortwave CRH of the SLC （MLC） reaches a heating peak at 9.75 （7.5） km, with a value of 0.35 （0.60） K day-1, and the differences between SLC and MLC transform from positive to negative with increasing altitude. However, the longwave CRH of the SLC （MLC） reaches a cooling peak at 2 （8） km, with a value of -0.45 （-0.42） K day-1, and the differences transform from negative to positive with increasing altitude. In general, the NET CRH differences between SLC and MLC are negative below 7.5 km. These results provide an observational basis for the assessment and improvement of the cloud parameterization schemes in global models.

Modeling Study of the Global Distribution of Radiative Forcing by Dust Aerosol

To quantitatively understand the dust aerosol effects on climate change, we calculated the global dis-tribution of direct radiative forcing due to dust aerosol under clear and cloudy skies in both winter and summer, by using an improved radiative transfer model and the global distribution of dust mass concentra-tion given by GADS （Global Aerosol Data Set）. The results show that the global means of the solar forcing due to dust aerosol at the tropopause for winter and summer are -0.48 and -0.50 W m-2, respectively; the corresponding values for the longwave forcing due to dust are 0.11 and 0.09 W m-2, respectively. At the surface, the global means of the solar forcing clue to dust are -1.36 W m-2 for winter and -1.56 W m-2 for summer, whereas the corresponding values for the longwave forcing are 0.27 and 0.23 W m-2, respectively. This work points out that the absolute values of the solar forcing due to dust aerosol at both the tropopause and surface increase linearly with the cosine of solar zenith angle and surface albedo. The solar zenith angle influences both the strength and distribution of the solar forcing greatly. Clouds exert great effects on the direct radiative forcing of dust, depending on many factors including cloud cover, cloud height, cloud water path, surface albedo, solar zenith angle, etc. The effects of low clouds and middle clouds are larger than those of high clouds. The existence of clouds reduces the longwave radiative forcing at the tropopause, where the influences of low clouds are the most obvious. Therefore, the impacts of clouds should not be ignored when estimating the direct radiative forcing due to dust aerosol.

Evaluation of Cloud Vertical Structure Simulated by Recent BCC_AGCM Versions through Comparison With CALIPSO-GOCCP Data

ABSTRACT The abilities of BCC-AGCM2.1 and BCC_AGCM2.2 to simulate the annual-mean cloud vertical structure （CVS） were evaluated through comparison with GCM-Oriented CALIPSO Cloud Product （CALIPSO-GOCCP） data. BCC-AGCM2.2 has a dynamical core and physical processes that are consistent with BCC-AGCM2.1, but has a higher horizontal resolution. Results showed that both BCC-AGCM versions underestimated the global-mean total cloud cover （TCC）, middle cloud cover （MCC） and low cloud cover （LCC）, and that BCC_AGCM2.2 underestimated the global-mean high cloud cover （HCC）. The global-mean cloud cover shows a systematic decrease from BCCA-GCM2.1 to BCC_AGCM2.2, especially for HCC. Geographically, HCC is significantly overestimated in the tropics, particularly by BCC_AGCM2,1, while LCC is generally overestimated over extra-tropical lands, but significantly underestimated over most of the oceans, especially for subtropical marine stratocumulus clouds. The leading EOF modes of CVS were extracted. The BCC_AGCMs perform well in reproducing EOF1, but with a larger variance explained. The two models also capture the basic features of EOF3, except an obvious deficiency in eigen- vector peaks. EOF2 has the largest simulation biases in both position and strength of eigenvector peaks. Furthermore, we investigated the effects of CVS on relative shortwave and longwave cloud radiative forcing （RSCRF and RLCRF）. Both BCC_AGCM versions successfully reproduce the sign of regression coefficients, except for RLCRF in PC1. However, the RSCRF relative contributions from PC1 and PC2 are overestimated, while the relative contribution from PC3 is underes timated in both BCC_AGCM versions. The RLCRF relative contribution is underestimated for PC2 and overestimated for PC3.

Analytical Studies of the Cloud Droplet Spectral Dispersion Influence on the First Indirect Aerosol Effect

Atmospheric aerosols （acting as cloud condensation nuclei） can enhance the cloud droplet number concentration and reduce the cloud droplet size, and in turn affect the cloud optical depth, as well as the cloud albedo, and thereby exert a radiative influence on climate （the first indirect aerosol effect）. In this paper, based on various relationships between cloud droplet spectral dispersion （c） and cloud droplet number concentration （Nc）, we analytically derive the corresponding expressions of the cloud radiative forcing induced by changes in the cloud droplet number concentration. Further quantitative evaluation indicates that the cloud radiative forcing induced by aerosols for the different ^-Nc relationships varies from -29.1% to 25.2%, compared to the case without considering spectral dispersion （e = 0）. Our results suggest that an accurate description of e - Nc relationships helps to reduce the uncertainty of the first indirect aerosol effect and advances our scientific understanding of aerosol-cloud-radiation interactions.

Cloud Variations under Subtropical High Conditions

The cloud variations under subtropical high(STH) conditions during summers over a ten-year period are studied using combined data from the International Satellite Cloud Climatology Project and the National Centers for Environmental Prediction.The results reveal that clouds mainly experience an isolated evolution in the STHs,which is designated in this study by the 1540 gpm geopotential lines at 850 hPa.In the STH domain throughout the Northern Hemisphere,the average amount of total clouds exceeds 30%.Low clouds dominate in the STH domain,contributing over 60%of total cloud amount within the Pacific subtropical high and over 40%within the Atlantic subtropical high.The prevalence of low clouds in above regions is determined by the circulation pattern around 150°-180°E and 850 hPa,which suppresses both the upward development of the cloud tops and the water vapor divergences near the surface.Furthermore,clouds present great geographical incoherence within the STH domain.In the eastern STHs,the amount of middle and low clouds increases to peak in the early morning and decreases to a trough in the afternoon,while the amount of high clouds remains stable throughout the day.Conversely,in the western STHs,the diurnal amplitude of low and middle clouds is less than three,while high clouds dramatically reach the maximum in the afternoon and drop to the minimum in the evening.Among the nine cloud categories,stratocumulus clouds with greater optical thickness account for the most under STH conditions,no matter their occurrence or amount,causing more shortwave cloud radiative forcing to cool the local atmosphere and surface as a consequence.

Evaluating the Impacts of Cloud Microphysical and Overlap Parameters on Simulated Clouds in Global Climate Models

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.

Model Analysis of the Anthropogenic Aerosol Effect on Clouds over East Asia

A coupled meteorology and aerosol/chemistry model WRF-Chem(Weather Research and Forecast model coupled with Chemistry) was used to conduct a pair of simulations with present-day(PD) and preindustrial(PI) emissions over East Asia to examine the aerosol indirect effect on clouds.As a result of an increase in aerosols in January,the cloud droplet number increased by 650 cm-3 over the ocean and East China,400 cm-3 over Central and Southwest China,and less than 200 cm-3 over North China.The cloud liquid water path(LWP) increased by 40-60 g m-2 over the ocean and Southeast China and 30 g m-2 over Central China;the LWP increased less than 5 g m-2 or decreased by 5 g m-2 over North China.The effective radius(Re) decreased by more than 4 μm over Southwest,Central,and Southeast China and 2μm over North China.In July,variations in cloud properties were more uniform;the cloud droplet number increased by approximately 250-400 cm-3,the LWP increased by approximately 30-50 g m-2,and Re decreased by approximately 3 ?m over most regions of China.In response to cloud property changes from PI to PD,shortwave(SW) cloud radiative forcing strengthened by 30 W m-2 over the ocean and 10 W m-2 over Southeast China,and it weakened slightly by approximately 2-10 W m-2 over Central and Southwest China in January.In July,SW cloud radiative forcing strengthened by 15 W m-2 over Southeast and North China and weakened by 10 W m-2 over Central China.The different responses of SW cloud radiative forcing in different regions was related to cloud feedbacks and natural variability.

Downward surface shortwave radiation over the subtropical Asia-Pacific region simulated by CMIP5 models

本文以两套卫星观测资料为参考,评估了15个CMIP5气候模式对亚太地区太阳总辐射(DSSR)的模拟能力,并将亚太地区按经度位置划分成五个子区域来更好地分析模式误差的成因。许多CMIP5模式在海洋上低估了DSSR,而在陆地上却高估了DSSR。除了地中海-西亚(MWA)和中亚(CA),在年平均或季节平均尺度上,地表短波云辐射强迫(CRF)的误差都能很好地解释CMIP5模式中DSSR的主要误差来源:模式在海洋上高估了CRF的影响,而在陆地上低估了CRF的影响。云是影响亚太地区CMIP5模式中DSSR质量的主要因素,但是其在MWA和CA区域的影响相对较弱,特别是在北方的夏季和秋季。

基于云辐射强迫的太阳辐射短期预报模型

太阳能持续性模型常被用作基准模型以评估其他模型的预报性能,但有云时的预报准确率很低。基于云相对辐射强迫(RCRF)的持续性,构建了RCRF模型。它能更好地预报有云时段的太阳辐照度。利用美国南部大平原中心站长达16年的太阳辐射资料,通过一个有云个例和所有样本评估了新模型的预报性能,并与应用最广泛的Simple模型作对比。结果表明:新模型的预报性能优于Simple模型,百分比误差评分(S)评估结果显示新模型6 h预报精度相较于Simple模型最大可提高至56%,预报时效也延长了0.25~2 h不等。RCRF模型为太阳能预报模式提供了准确率更高的基准模型。

华北地区沙尘气溶胶对云辐射强迫的影响

采用CERES SSFAqua MODIS Edition 2B/2C和CALIPSO卫星探测资料结合地面台站沙尘观测资料,通过对强沙尘天气过程中纯云区与沙尘云区大气层顶处辐射强迫值的对比分析,研究了我国华北地区沙尘气溶胶对云辐射强迫的影响.研究发现,2006年4月16日、5月16日、2007年3月30日3次过程沙尘云区大气层顶云的净辐射强迫绝对值比纯云区分别减小了7.1%,17.2%和3.1%,云的冷却效应受到不同程度抑制.纯云区与沙尘云区云的光学特性参量的对比分析结果表明,绝大部分沙尘云区的云粒径、云水路径和光学厚度值均比纯云区的要小.

LASG/IAP和BCC大气环流模式模拟的云辐射强迫之比较

通过与ISCCP(International Satellite Cloud Cli matology Project)逐月辐射资料的比较,本文从气候态和对ENSO响应的角度,评估了国内的三个大气环流模式BCC AGCM、IAP GAMIL和IAP SAMIL对云辐射强迫的模拟能力,讨论了影响模拟结果不确定性的因素。分析表明,三个模式均能较为合理地再现年平均长、短波云辐射强迫及净云辐射强迫的空间分布型,其与ISCCP资料年平均结果的空间相关系数,均超过了1%水平的信度检验。定量比较表明,除部分区域外,模式模拟的云辐射强迫的强度与ISCCP资料相比存在显著差异,尤以副热带大洋最为显著。三个模式模拟的云净辐射强迫在赤道外北太平洋、热带东南和西南太平洋存在显著的偏差。分析表明,造成上述模拟偏差的原因,一是对流的模拟偏差,二是云方案,二者导致模式无法合理再现观测中的云量分布、云垂直结构(云高度、云厚等)和云光学属性,最终导致云辐射强迫的模拟偏差。此外,在年际变率方面,模式基本模拟出ENSO期间云净辐射强迫"东正西负"的响应分布型,但是BCC AGCM和IAP SAMIL在西太平洋的负响应偏强,而IAP GAMIL的响应偏弱且中心位于赤道中太平洋。

一维辐射对流模式对云辐射强迫的数值模拟研究

利用一维辐射对流气候模式,详细研究了云量、云光学厚度以及云高等要素的变化对大气顶和地面太阳短波辐射和红外长波辐射通量以及云的辐射强迫的影响,给出了计算这些物理量的经验拟合公式。结果表明,云具有极为重要的辐射气候效应。云量、云光学厚度以及云高即使只有百分之几的变化,所带来的辐射强迫也可以与大气二氧化碳浓度加倍所产生的辐射强迫(3.75 W/m2)相比拟。例如,当分别给它们+3%的扰动时,即取云量变化0.015,云光学厚度变化0.27,以及云高变化0.15 km时(在实际的地球大气中,这种尺度的变化是完全可能发生的),那么,可以得到地气系统的太阳短波辐射强迫-3.10 W/m2以及红外长波辐射强迫-1.77 W/m2,二者之和为-4.78 W/m2,已经完全可以抵消大气二氧化碳浓度加倍所产生的辐射强迫。但是,当云量、云光学厚度以及云高向相反方向产生类似扰动时,所产生的辐射强迫可能极大地放大二氧化碳浓度增加所产生的增强温室效应。因此,研究结果揭示出,不管是为了解释过去的气候变化,还是预测未来的气候变化,亟待加强在一个变化了的气候环境(例如地面温度升高)下,云将发生何种变化的研究。