典型站点气溶胶对云特性的影响

结合Cloud Sat对云的主动观测和MODIS(MODerate-Resolution Imaging Spectroradiometer)对气溶胶的被动反演,研究了典型站点气溶胶对云的宏观、微观和辐射特性的影响。结果表明,气溶胶对大陆性和海洋性站点的云均有显著影响。1)随气溶胶光学厚度(Aerosol Optical Depth,AOD)增加,水汽含量较弱站点的低层(高层)云量呈减小(增加)趋势,而水汽条件较强站点的各层云量均增大,且具有较高(较低)云顶的云层发生概率在各个站点都呈增加(减小)趋势。2)AOD的增大导致各站点云滴和冰晶粒子的有效半径均减小、大气层顶的短波和长波云辐射强迫均增强、短波云辐射强迫绝对值的加强更显著、长波云辐射强迫增加的幅度相对更大。3)气象要素在AOD大(小)值情况下的变化表明,大尺度动力条件并不能解释云的上述特性随AOD的显著改变。

Impact of aerosols on cloud properties at typical sites

The effects of aerosols on cloud macro-physical,microphysical and radiative properties at typical sites are analyzed using the objective cloud observations from CloudSat and the passive aerosol retrievals from MODIS(Moderate-Resolution Imaging Spectroradiometer).Results show that aerosols have significant impact on cloud over both continental and marine sites.With the increase of aerosol optical depth(AOD),the low(high) level cloud fraction at sites with relative weak water vapor conditions shows decrease(increase) trend,while the cloud fraction of all altitudes increases at sites with relative strong water vapor conditions.With the increase of AOD,occurrence probabilities of cloud layers with high(low) cloud top height at each site show an increase(a decrease) trend.With the increase of AOD,the effective radius of cloud droplet and ice crystal decrease,both the shortwave and longwave cloud radiative forcings at atmosphere top are enhanced,the increase of absolute value of shortwave cloud radiative forcing is large,and the increase of longwave cloud radiative forcing is relatively larger at all sites.The variations of meteorological elements under large(small) AOD conditions indicate that the significant changes of cloud physical and radiative properties with AOD can not be explained by large scale dynamical influence.