Abstract: Large eddy simulations were used to get profiles of liquid water content and droplet effective radius in shallow cumulus clouds. Results show that both liquid water content and droplet effective radius increase with height (vertically inhomogeneous). Then the atmospheric radiative transfer model SBDART were used to study the effects of vertical distributions of microphysical properties on radiative transfer. The shortwave radiative forcings from a vertically inhomogeneous cloud and a vertically homogeneous cloud with the same liquid water path were compared. Results indicate that vertical distributions of microphysical properties have significant effects on radiative transfer. When droplet effective radius of the vertically homogeneous cloud is equal to 76% -90% of the cloud-top droplet effective radius in a vertically inhomogeneous cloud, the two clouds have similar radiatve forcing. This means that in global climate models, the assumption of vertical homogeneity of a cloud must be used carefully and the associated droplet effective radius must be about 76% -90% of the observed value at cloud top for shallow cumulus clouds. Results in this study are consistent with previous studies for stratified clouds.

Key words: vertically inhomogeneous clouds, SBDART, shortwave radiative forcing , shallow cumulus clouds

摘要： 使用大涡模拟模式获得浅积云的液态水含量和云滴有效半径的垂直廓线, 结果显示云的液态水含量和云滴有效半径均随高度的增加而增加( 垂直非均一) 。使用辐射传输模式 SBDART 研究了浅积云中微物理特性的垂直廓线对短波辐射的影响, 以及液态水路径相同时, 垂直非均一云和垂直均一云的短波辐射强迫的差异, 结果表明微物理特性的垂直廓线对云的辐射特性有很大影响。当垂直均一云的云滴有效半径约为垂直非均一云在云顶处的云滴有效半径的76% ～90% 时, 两种类型云的短波辐射强迫相当。结果说明在气候模式中对云的辐射传输特性进行参数化时, 如果假定云是垂直均一的, 则采用的云滴有效半径应该大致为实际观测的云顶云滴有效半径的76% ～90% 。对于浅积云的研究结果与以往对于层状云的研究结果一致。

关键词: 垂直非均一云, SBDART, 短波辐射强迫, 浅积云