一次华南暴雨过程的数值模拟——中尺度对流系统形成发展机制

摘要

During 12-13 June 2008, a heavy rainfall event mainly caused by the successive mesoscale convective systems (MCSs), which experienced genesis, merging and intense development, occurred in southern China. By using a new generation mesoscale model of Weather Research and Forecasting (WRF), this heavy rainfall event is simulated, and the mechanisms of MCSs genesis, development and evolution are also analyzed. During the genesis of MCSs, they were located in the environment with positive vorticity due to the presence of the southwest vortex. Both of the convergence at lower levels induced by positive vorticity and static instability are important mechanisms for convective initiation. The collective effects from them are favorable to the convective initiation and enhancement. After generation,MCSs can influence the surrounding vorticity by tilting in the strong vertical shear environment, and then the change of surrounding vorticity will affect the MCSs. This positive feedback causes the rapid development of MCSs. In the process of interactions between these strengthened MCSs and environmental flow,the merging of MCSs is completed. In addition, the Magnus force acts on the splitting of MCSs.%2008年6月11-13日在华南地区出现了特大暴雨,这主要是由一系列中尺度对流系统(MCS)的相继生成,合并和强烈发展导致的.该研究利用新一代中尺度数值模式WRF对此次暴雨过程进行数值模拟,重点研究此次强降水过程中MCS发生、发展和演变过程及其相关物理机制.在MCS的生成过程中,由于西南涡的存在导致MCS始终处于正涡度环境中,正涡度导致的低层辐合与大气静力不稳定都是重要的MCS启动机制,这两者的共同作用有利于MCS的生成与加强.MCS形成后,在强垂直切变的环境中,倾斜抬升机制发生作用,更进一步加强了环境涡度,形成有利的正反馈过程,造成MCS迅速发展.这些加强的MCS和大尺度环境流场相互作用,造成了它们的合并.在MCS的分裂过程中,马氏力起着重要作用.