气候模式中云的垂直重叠假定对模拟的地-气辐射的影响研究  

Effect of Cloud Overlap Assumptions in Climate Models on Modeled Earth-Atmosphere Radiative Fields

作　　者：张华[1] 荆现文[1,2] 

机构地区：[1]中国气象局气候研究开放实验室国家气候中心,北京100081 [2]中国气象科学研究院,北京100081

出　　处：《大气科学》2010年第3期520-532,共13页Chinese Journal of Atmospheric Sciences

基　　金：科技部公益性行业(气象)科研专项经费GYHY200706036;国家重点基础研究发展计划项目2006CB403707

摘　　要：本文将一种新的可以模拟云的多种垂直重叠假定的随机次网格云产生器(SCG)放入NCAR/CAM3气候模式中,利用该产生器得到云的四种垂直重叠结构,即最大重叠(MO)、随机重叠(RO)、最大-随机重叠(MRO)以及近年来发展的一般重叠(GenO),并以GenO为参照研究了这四种云的重叠结构对模拟的地-气辐射的影响,为气候模式中云的次网格结构选择提供一定的依据。结果表明,MRO、MO和RO总云量分别与Ge-nO总云量(全球平均0.64左右)偏差约-0.012、-0.034和0.026,其中MRO最接近GenO。不同重叠假定对地面接收到的短波辐射通量(DSR)的改变显著,在热带对流区达到16W/m2以上,相当于GenO下该地区相应量的8%～12%,通过了95%信度检验;在中高纬度低云量大的地区也达到4～8W/m2。不同重叠假定对大气顶出射长波辐射(OLR)的改变比其对短波辐射通量的改变小得多,在热带对流区有极大值3～4W/m2。不同的云重叠结构的大气加热率垂直廓线不同,从而影响大气热力结构,其中长波加热率差值(最大约0.1～0.26K/d)比短波加热率差值(最大约0.01～0.025K/d)几乎大一个量级,因此,长波加热率的变化是影响大气热力层结的主要因素。云重叠假定影响地面和大气顶云辐射强迫,并通过柱辐射强迫使得整层气柱的能量收支发生变化,不同纬度变化趋势也不同,从而系统性地改变地-气系统能量在各纬度地区的分配,影响所模拟的气候系统的演变。Weather generators were useful for generating incomplete history weather records and weather scenarios in future.Recently they were used to study downscaling climate variables and provide weather forcings for hydrological and ecological simulations.Generalized linear models（GLM） are powerful tools for relating large-scale weather variables with high resolution variables at the earth surface.The application of generators based on GLM is promising.In this paper,by using five variables derived from single grid NCEP reanalysis data,such as air temperature,500-hPa geopotential height,potential temperature,relative humidity,sea-level pressure,as large-scale independent variables that affect precipitation variations,GLM for downscaling and simulating daily precipitation were constructed.For determination of precipitation occurrence probability,the logistic model was used,and for simulating daily precipitation amounts,the Gamma,exponential,normal,and lognormal distributions were used respectively.The observed daily precipitation series and the selected NCEP reanalysis data were used for parameter-estimation and simulation.The maximum likelihood estimate of the model parameters was performed by genetic algorithms.The results of estimation showed that the fitting effect of the gamma distribution-based models was the best,the lognormal distribution was the second,the exponential distribution was the third,and the fitting effect of the normal distribution-based models was the worst;on the other hand,the fitting effect of the models with their parameters estimated for each month separately was a little better than that without separation of months.Both the observed and simulated daily precipitation-occurrence probabilities were added for each month and the corresponding precipitation amounts were also averaged for each month in order to verify the models＇ ability.Results showed that the precipitation-occurrence probability was underestimated slightly by the logistic model,and precipitation-amounts expectations were unde

关 键 词：云垂直重叠 全球气候模式 随机云产生器 

分 类 号：P422[天文地球—大气科学及气象学]