.99.6 Meiyu Front Rainstorm Cloud Physical Processes And Mm5 Numerical Study Of The Wet Physical Processes

The Meiyu rainstorm case on the Yangtze River during from 27 June to 28 June 1999 is simulated by the meso-seale model MM5 developed by PSU/NCAR. The simulation results reveal that convective parameterization Kain-Fritsch and Grell schemes, which are designed for mesoscale applications and include parameterized moist downdrafts, demonstrate considerable skill in simulating the position and timing of important observed meso-scale featuers, especially, Grell scheme succeeded in simulating a meso-p scale vortex in rainfall region.The experiments of explicit microphysical schemes showed that the simple super-saturation removal scheme can produce excessive amounts of resolvable-scale precipitation due to the unrealistic microphysical treatment in it, and the warm rain scheme can improve simulation skill significantly. The double-moment microphysical scheme(Reisner), in which both ice mixing ratio and number concentration were predicted, performed best, with close to the observed fields. The simulation cloud fields of the Reisner scheme accorded with observed features, which enucleated that explicit microphysical scheme including ice phase process can reproduce meiyu front features of cloud field. The results can be used to analyze the effects of ice phase process in forming precipitation, and can explain the observed "Seeder-Feeder" phenomena. Finally, by analyzing the vertical cross-sections of water substances of this rainstorm, it can be found that the warm rain processes was the major process in cloud of above heavy rainfall region, and the cold cloud processes was the major process in light rainfall region.