Research On The Impact Of PBL Parameterizations To The Summer Precipitation In China And The Cause

The meso-scale structure of rainstorm is a vital issue for atmosphere science, which can reveal the developing process and the dynamic scheme of rainstorm. Research show that the planetary boundary layer (PBL) processes are very important for the developing of rainstorm because there are vertical transfer of energy, heat, and vapor in the PBL, So the PBL numeric model is also important for rainstorm numeric simulation.In the paper, the fifth-generation Pennsylvania State University-National Center for Atmospheric Research Meso-scale Model(MM5) is used to simulate the rain in the south China and in June 2002. Numeric experiments are conducted to determine the sensitivity of rainstorm simulation to the available PBL parameterizations, Which is Burk -Thompson boundary layer scheme and Medium-Range Forecast(MRF) model. The results show that both of the two schemes can predict the rainstorm in the south China in June 2002, and can simulate the main heavy-rain region and the rainstorm center, but simulate different rainstorm region and intensity.The PBL schemes in MM5 show apparent different in their formulations of the vertical mixing and the surface flux each other. The PBL exert influence on the rainstorm by affecting vertical transfer of energy, heat, and vapor. The main analysis are focused on the impacts of the surface fluxes and the vertical mixing in selected PBL parameterizations on vertical transfer of energy, heat, and vapor. The results indicate that the parameterizations of surface flux exert much stronger influence on the vertical transfer of energy, heat, and vapor simulation than the parameterizations of vertical mixing, the rainstorm simulation is largely determined by the surface fluxes rather than by the vertical mixing. Detail analyses show that the surface flux of latent heat play more crucial part than the surface flux of sensible heat on the rainstorm simulation.The start time of precipitation simulated by MRF scheme is later than by Burk -Thompson scheme because the surface roughness parameter is dealt with more simple in MRF scheme than in Burk -Thompson scheme.