基于CloudSat卫星资料的青藏高原云系发生频率及其结构

Cloud Occurrence Frequency and Structure over the Qinghai-Tibetan Plateau from CloudSat Observation

应用2006年5月至2013年5月7年的Cloud Sat卫星观测资料,针对青藏高原上空不同高度、不同季节8类云(卷云、高层云、高积云、层云、层积云、积云、雨层云、浓积云)的发生频率,分析研究了青藏高原地区云的水平和垂直分布特征及其物理成因,为数值预报模式对云系模拟能力的评估提供了有效的验证信息。研究表明:青藏高原云的发生频率为35%,其中:低云的频率最大,接近21%;中云次之,频率14%;高云的频率最小。垂直分布上,低云最大频率的高度为5~6 km,中云为7~8 km,高云为11~12 km。水平分布上,高原东南部、西北部云发生频率较高,是高原的两个相对多云中心。低云与总的云频率水平分布基本一致;中云是高原北部、中部频率高,南部低,与低云明显不同;高云主要是夏季在高原南部频率高。从不同季节来看,冬季高原西部的低云频率高;春季高原中北部的中云频率高,西部和东南部的低云频率高;夏季南部的低云和高云频率高;秋季云发生频率都很低。在物理成因上,低云的形成主要是地形抬升作用,中云的形成与高原热力作用相关。

By using 7-year（Data time series from May 2006 to May 2013） CloudSat observations,occurrence frequencies of 8 cloud types for different levels and seasons over the Qinghai-Tibetan Plateau are constructed to examine characteristics of their horizontal and vertical distributions and related physical causes,which could provide observational information for evaluating cloud simulated by numerical weather prediction models. It is found that the frequency of total cloud occurrence is about 35%. Among low,middle and high clouds,the highest frequency is low cloud near 21%,followed by middle clouds about 14%,and the lowest one is high cloud less than1%. In terms of vertical structure,the maximum frequency of low clouds at a height of 5 ~ 6 km,7 ~ 8 km for middle clouds and 11~12 km for high clouds. High frequency of total cloud occurrence is located in the Southeast and Northwest parts of the Qinghai-Tibetan Plateau which forms two centers of relatively plentiful clouds.The spatial distribution of low cloud frequency is consistent with that of total clouds,middle cloud frequency is high in the north and middle Plateau and low in the South Plateau which is obviously different with low cloud and on the other hand,high cloud frequently occurs in the South Plateau. For seasonal variation,in terms of high frequency of occurrence,during winter low cloud is over the west Plateau; During spring middle cloud over the middle north part and low clouds over the west and southeast; During summer high and low clouds over the south of the Plateau. There is very low occurrence frequency for all kinds of clouds during fall. It was indicated that the formation of low clouds is mainly due to orographic uplift,and middle clouds largely associated with the thermosdynamical effects of the Plateau.