Nonhydrostatic Numerical Simulation and Analyses on the Mesoscale Systems of “98.5” Heavy Rain in the South China Preflood Season

In order to study in detail the heavy rain event of South China, the simulation for !98.5 heavy rain using the nonhydrostatic mesoscale numerical model was conducted on the basis of synoptic analysis of heavy rain on 23~24 May 1998 (!98.5). The comparions between the simulated results and objective analysis have shown that the simulated results reappeared the large- and meso-scale circulations. The mesoscale system producing this heavy rain has the warm and wet core. Divergence on upper levels, convergence on low levels,and ascending motion as well as the cyclonic vorticity column are the dynamic mechanisms causing the heavy rain. The southwest jet over low levels is importantfor this heavy rainfall. The centre of the simulated precipitation is close to that of the observed, but its location is southward and westward, rainfall is light. Their simulated precipitation is smaller than the observed. Rainfall usually occur in favorable terrain in where is the bell-mouthed. Simulated results using differentterrain data of high or low resolutions were similar.