TRMM卫星对一次冰雹降水过程的观测分析研究

利用TRMM卫星上时空匹配较好的测雨雷达(PR)、微波成像仪(TMI)、可见光和红外扫描仪(VIRS)观测资料,研究了1999年5月9日发生在黄淮地区的一次冰雹降水过程。根据卫星接连3个轨道的观测,综合分析了此次强对流降水过程在不同阶段的降水结构、云顶亮温和降雨厚度以及相应的微波亮温变化特征。观测分析表明,此次降水过程由对流很强的冰雹降水逐渐演变到对流渐弱的暴雨降水。冰雹降水阶段,云中有多个强对流单体,云体中高层有大量的固态降水粒子,使得中高层降水量在降水柱含量中贡献远大于融化层降水量的贡献;暴雨降水阶段,若干对流单体被大面积的层云降水包围,降水高度逐渐降低,云体中高层降水量明显减少,融化层降水量对柱含量的贡献明显增加。降水率廓线中不同高度的降水量对降水柱含量贡献的比较表明:中高层降水量占的比例越大,降雨云对流越强,反之,融化层降水量占的比例越大,降雨云越趋向为稳定的层云。微波亮温信号在不同降雨阶段随雨强的响应程度大不相同,这表明在反演地面降雨时,最好结合降雨云的结构特征及其发展阶段,针对不同降雨类型选取最为有效的微波通道组合来建立最佳反演模式。

ANALYSES OF EVOLUTIONAL CHARACTERISTICS OF A HAILSTORM PRECIPITATION FROM TRMM OBSERVATIONS

A hailstorm occurring on May 9,1999 in the Huanghuai region is studied by using the combined data from the precipitation radar(PR),microwave imager(TMI),and visible infrared scanner(VIRS) on the Tropical Rainfall Measuring Mission(TRMM) satellite.According to the 3 successive orbit observations of 4-hour duration from TRMM satellite,the evolutional characteristics of the precipitation structures as well as cloud top brightness temperature and microwave signatures of the precipitating cloud are comprehensively analyzed for hail-and rain-storm stage.The analysis results show that the precipitation process evolved gradually from the hail-precipitation in the early stage i.e.the hail-storm stage with strong convection,into the later stage,i.e.the rainstorm stage with weakening convection.In the early stage,there existed several strong convective cells in the hail-cloud,and there was so much solid precipitation in the middle-upper layer that the contribution of rainfall amount above the freezing-layer to the whole column precipitation amount is far greater than that within the melting-layer.However,in the rain-storm stage,the convective cells were surround by a vast stretch of stratiform clouds,and the height of precipitating layer was gradually reduced,the rainfall above the freezing-layer obviously reduced,and thus the contribution of rainfall amount within the meltinglayer rapidly increased.Comparison of the contribution of the rainfall at different heights to the total column rainfall indicates that the larger the proportion of the rainfall above the freezing layer in the total column precipitation amount,the more intense the convection in the precipitating cloud.Inversely,the larger proportion of the rainfall within the melting layer means that the precipitating cloud is more stable(stratiform clouds).The different response trends of microwave signatures to precipitation rate in different precipitation stages suggest that it is better to consider at first the structures and stages of precipitating cloud,and then to choose the best microwave channels in the retrieval of surface rainfall.