STRUCTURES OF A THERMAL CONVECTIVE PRECIPITATION SYSTEM HAPPENED IN CONTROLLING OF THE WESTERN SUBTROPICAL PACIFIC HIGH

A thermal convective precipitating cloud system occurred in the southeastern mainland of China at 15:00 on August 2, 2003 under controlling of the western subtropical Pacific high was studied by using TRMM PR and IR measurements. Rainfall structures in both horizontal and vertical, relationship among rain-top, cloud-top and surface rainfall rate were particularly analyzed. Results show that a strong ascending air at 500 hPa and a strong convergence of moisture flux at 850 hPa near the center of the western subtropical Pacific High supply necessary conditions both in dynamics and moisture for the occurrence of the thermal convective rainfall system. TRMM PR detective shows that the horizontal scale of the thermal convective precipitating clouds are about 30-40 km mainly, and their averaged vertical scale is above 10 km, the maximum can reach to 17.5 km. The maximum rainfall rate near surface of those clouds is beyond 50 mm/h. The mean precipitation profile of those clouds shows their maximum rainfall rate at 5 km altitude that is 1 km lower than the estimated freezing level of the environment. Comparing with the mesoscale convective system of “98.7.20”, both systems have the same altitude of the maximum rainfall rate displayed from both mean precipitation profiles. But the thermal convective precipitating system is much deeper than that mesoscale convective system. From 4 km to near surface, profiles show that rainfall rate reducing in the thermal convective system is faster than that in the mesoscale convective system, which implies a strong droplet evaporation process occurring in the former system. Relationship among cloud-top, rain-top and surface rainfall rate analysis indicates a large amplitude variation of cloud-top when rain-top is lower. On the contrary, the higher the rain-top, the more consistent both cloud-top and rain-top is. Generally, cloud-top is 1-4 km higher than rain-top for a given surface rainfall rate. The bigger the surface rainfall rate, the higher and more consistent both cloud-top and rain-top is. Finally, results reveal that area fractions of no-precipitating clouds and clear sky are 86% and 2%, respectively. The area fraction of precipitating clouds is only about 1/8 that of no -precipitating clouds.