Wuhan 98721 Heavy Precipitation Numerical Simulation Study

Using the three-dimensional numerical model of convective rainstorm, IAP-CSM2, the severe rainstorm occurring in Wuhan on the morning of 21 July 1998 was simulated to analyze the structure and development of convective cloud and precipitation, and to deeply study the microphysical mechanism of rainfall. As a comparison, another case occurring in Shannxi in the evening of 20 July 1999 was chosen.By comparison the modelling results and observed data, this model can simulate the cloud developing structure and precipitation of convective rainstorm better. The modeling results show that the microphysical processes are important to local precipitation. The convective cloud of Wuhan case developed more stably. Its main microphysical process of cloud development is warm-cloud process, and cold-cloud process can promote- the formation of rainwater and precipitation. Though maximum updraft velocity, water contents of precipitation particles and instantaneous precipitation intensity of Wuhan case are all smaller, its cumulative precipitation is more than that of Shannxi case, because of its longer life span.The effects of convergence and humidity of low atmosphere on cloud and precipitation were simulated, in consideration of the aforementioned distinction. Results shows that convergence and higher humidity of lower atmosphere are all considerably advantageous to the development of cloud and precipitation. The combining effect of these two factors make the cloud develop longer and enhanced the precipitation intensity. Rich vapor provision and convergence are two important reasons to this Wuhan severe rainstorm.