基于CloudSat–CALIPSO资料的全球不同类型云的水平和垂直分布特征

Horizontal and Vertical Distributions of Clouds of Different Types Based on CloudSat-CALIPSO Data

基于Cloud Sat-CALIPSO(Cloud Sat–Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observations)卫星观测资料,分析了全球总云量和8类云的云量、云底高、云顶高、云厚度的水平和垂直分布。分析结果表明,全球平均总云量为66.7%,其中卷云(Ci)和层积云(Sc)云量之和与其他6类云量总和相当,是全球云量最多的两类云。积状云云量呈现从赤道向极地递减的特征,层状云则相反,反映了二者不同的生成环境,同时下垫面地形和天气系统也严重影响云的分布。8类云的高度及厚度特征有显著差异。Ci的云底高度和云顶高度都较高,厚度则较薄;高层云(As)和高积云(Ac)的云底高度和云顶高度都位于大气中层,但As比Ac出现的高度高且厚度大;层云(St)、层积云和积云(Cu)的云底高度和云顶高度都很低,属于薄的低云;雨层云(Ns)和深对流云(DC)云底较低但云顶伸展很高,归属于厚云类。总体而言,海洋上云底高度较陆地低;赤道等大气不稳定地区,云底较高,云厚度较大;高原地区则表现出"高云不高,低云不低,云厚较薄"的特征。

Global mean total amount of clouds is 66.7%. The total cloud fraction of Cirrus（Ci） and Stratocumulus（Sc） clouds is comparable to the sum of clouds of other six types, indicating that Ci and Sc clouds are two most frequently occurring cloud types over the globe. The amount of cumuliform clouds decreases from tropical to subtropical, while the amount of stratiform clouds changes in the opposite direction, indicating different environments for the formation of cumuliform and stratiform clouds. The topography and synoptic systems can affect cloud occurrence too. The cloud height and thickness of eight types of clouds are significantly different in different regions. Ci clouds, with higher cloud base and top, are very thin. Altostratus（As） clouds and Altocumulus（Ac） clouds are mid-level clouds, but As clouds are thicker and located at higher levels than Ac clouds. Stratus（St）, Sc, and Cumulus（Cu） clouds are thin clouds occurring in the lower atmosphere. Nimbostratus（Ns） and deep convective（DC） clouds are thick clouds with lower cloud base and higher cloud top. Overall, the height of the cloud base over the ocean is lower than that over the land. The cloud base is higher and the cloud depth is thicker in relatively unstable atmosphere such as over the equator than in stable atmosphere. Clouds over the Plateau are characterized by the features that high-clouds are not high and low-clouds are not low while the cloud depth is usually thin.