Abstract: Based on the daily NCEP/NCAR reanalysis data, the conventional and intensive observational data, the brightness temperature (TBB) from FY2C, the large-scale circulation background and mesoscale convective system of two heavy rainfall time periods in a torrential rain process on August 28-30, 2008 in Hubei province were diagnosed, and other physical quantities fields influencing this process were also analyzed by WRF model. The results indicate that there are two significantly precipitation enhancement time periods in this process, and both durations from the beginning to the end are same. Precipitation intensity is stronger in the second period than in the first one. The first heavy rainfall time period is formed by low vortex shear and surface warm moist airflow, while the second one is caused by low vortex shear, the middle and low level short wave trough and cold surface air. The hourly rainfall and cloud mass characteristics during the two periods suggest that motions of the rain mass and cloud mass are same, and enhancements of precipitation intensity appear at the night and early morning. It also suggests that the β mesoscale convective cloud cluster has a close relationship with the torrential rain process. The movement of warm shear line from south to north affects the rainfall enhancement in the first period, while that of cold shear line of southwest vortex from west to east affects the rainfall enhancement in the second. According to the model results, the increasing amplitude of rainfall in the second time is more significant. There is strong energy for two heavy rainfall periods over the study area. There exists the strong water vapor convergence in the whole process. The rainfall center at the surface has a good correlation with a large value center of the moist potential vorticity at upper level.

Key words: Torrential rain, Heavy rainfall, Cloud mass