西南低涡对流云团及其降水的一些特征

Characteristics of the Convective Cloud and Its Precipitation Associated with the Southwest Vortex

基于FY-2C静止卫星红外和水汽通道资料,简单分析了发生在四川盆地的西南低涡暴雨云团生消过程,给出了一些有意义的云团生命特征。同时,结合相应的地面自动站降水资料,详细分析了卫星红外和水汽通道云顶亮温与对流云团降水之间的关系特征,结果表明:对于一完整对流降水过程,1小时内最低水汽亮温和水汽亮温增量能很好地描述地面1小时累计降水特征。然而,用静止卫星红外或水汽通道亮温来表征的云团降水特征是非常复杂的。尽管具有相同的最低云顶红外或水汽亮温,但对不同的对流过程其总体降水量级趋势不一样。而且,对于同一对流过程的不同发展阶段,即使出现云顶红外或水汽亮温一样,但其地面降水特征也是不一致的。甚至是对于同一时刻具有相同最低红外或最低水汽亮温特征的云,其降水落区与量级都不尽相同。正是这些复杂的降水特征,使得西南低涡对流云团的降水估算具有很大的难度。

A simple analysis of the evolution of the convective cloud associated with the Southwest Vortex selected random- ly is performed based on the FY- 2C infrared （IR） and water vapor （IW） channel data in Sichuan Province. Some useful characterizations of convective cloud are found. Accordingly the analysis of the relationship between the cloud - top IR/IW brightness temperature and the rainfall is processed in combination with rainfalls from automatic meteorological observation sta- tion. It is found that rainfall rate over the past hour accumulation is, in general, related to the lowest IW brightness temperature and the change of IW brightness temperature in the past hour. Nevertheless, it is difficult to estimate the complex rainfall of the convective cloud using the cloud -top IR and IW brightness temperature data. There are different magnitudes of rainfalls pro- duced by convective clouds of different cases although their lowest IW brightness temperatures are same. There are individual characteristics of precipitations of convective clouds occurred in each period of evolution. Even though the lowest cloud - top IR/IW brightness temperatures of convective clouds in different areas are similar at a time, the distribution and magnitude of precipitations are not same. These characteristics result in the problem on rainfall estimate of convective cloud associated with the Southwest Vortex.