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 Rainf all Measuring Mission (TRMM) satellite. According to the 3 successive orbit obse rvations of 4 hour duration from TRMM satellite, the evolutional characteristic s 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 rain storm stage with weakening convection. In the early stage, there existed several s trong convective cells in the hail cloud, and there was so much solid precipita tion in the middle upper layer that the contribution of rainfall amount above th e freezinglayer to the whole column precipitation amount is far greater than th a t within the meltinglayer. However, in the rainstorm stage, the convective c el ls were surround by a vast stretch of stratiform clouds, and the height of preci pitating layer was gradually reduced, the rainfall above the freezinglayer obv i ously reduced, and thus the contribution of rainfall amount within the melting layer rapidly increased. Comparison of the contribution of the rainfall at differ ent heights to the total column rainfall indicates that the larger the proportio n of the rainfall above the freezing layer in the total column precipitation amo unt, the more intense the convection in the precipitating cloud. Inversely, the larger proportion of the rainfall within the melting layer means that the precip itating 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 prec ipitating cloud, and then to choose the best microwave channels in the retrieval of surface rainfall.