不同云重叠参数对全球和东亚地区模拟总云量的影响

Effects of different cloud overlapping parameters on simulated total cloud fraction over the globe and East Asian region

在国家气候中心全球大气环流模式BCC_AGCM2.0中引入一组基于CloudSat/CALIPSO卫星观测的、能够体现真实时空变化特征的云垂直重叠参数(抗相关厚度,L_(cf))数据,以减小由云的重叠描述造成的辐射场的不确定性。对比了采用时空变化的云重叠参数和采用恒定云重叠参数的气候模拟结果,发现无论在全球还是东亚区域,采用基于卫星观测的云重叠参数对模拟的总云量都有一定程度的改进。采用时空变化的云重叠参数后,冬、夏两季全球平均总云量与云和地球的辐射能量系统(CERES)卫星资料的误差都减少了1.6%,其中热带对流区域总云量的正偏差和副热带地区总云量的负偏差都明显减少,这些有助于正确模拟不同区域间的能量收支差异。在东亚区域,采用时空变化的云重叠参数后,冬、夏两季的东亚区域平均总云量与CERES卫星资料的误差分别减少了1.8%和1.4%。综上所述,基于CloudSat/CALIPSO卫星资料计算得到的L_(cf)有助于改进大气环流模式对总云量的模拟,从而提高模式对辐射场的模拟精度。

The cloud overlapping parameter（vertical decorrelation length,Lcf） from CloudSat/CALIPSO is implemented in Beijing Climate Center＇s GCM（BCC_AGCM2.0） to reduce the uncertainly in radiation field.Comparing the climate simulation results obtained by using the constant Lcf of 2 km with those using the above retrieved Lcf,it is found that the total cloud fraction simulation has been obviously improved by using the satellite-based Lcf.The error of global mean total cloud fraction between simulations and CERES（Clouds and the Earth＇s Radiant Energy System）satellite data is decreased by 1.6% in both the winter and summer,of which the positive deviation of total cloud fraction at tropical convection area and the negative deviation in subtropical region both are significantly reduced.These improvements are helpful for better simulation of energy budget differences between different regions.In East Asia,using the satellite-based Lcfcan decrease the error of average total cloud fraction（compared to the CERES）by 1.8%（1.4%） in the winter（summer）.Overall,using Lcf from CloudSat/CALIPSO satellite data can improve the simulation of total cloud fraction and thus obtain more accurate simulation of radiation field.