The Mechamism Analysis And Numerical Simulation Study On The Meiyu Heavy Rainfall On 5～(th) July 2003 In The Changjiang-Huaihe River Basin

A diagnostic analysis of a heavy rainfall over Changjiang-Huaihe River Basin in Ju1.4 to 5th in 2003 is made in this work. It is revealed that the heavy rainfall is mainly induced together by the trough at 500hPa , mesoscale vortex at 850hPa and stable Mei-yu front at surface. Analyzing the physics structure of vorticity, divergence, vertical velocity, frontogenesis "function, apparent heat source and apparent moist sink etc. indicated the physics fields are favorable for the occurance of the heavy rain over Changjiang-Huaihe River Basin where the physics values are well according to the heavy rainstorm positions; The low level jet is closely subject to the moisture and the coupled system of the low and the upper level jetstreams induced the strongly "ascending motion; the intensity of the frontogenesis varies with the development of the rainfall system and reacts the rainfall intensity. The variances of the apparent heat source, apparent moist sink and the heavy rainstorm are well coupled. The time the maximums of them appeared is quite accordance; the vertical advection term is the main contributor of the apparent heat source and apparent moist sink.The meso-scale model MM5 well reproduced the heavy rainfall process and the weather systems associated. Using the output with high spatial and time resolution of the model, the development of the meso-scale vortex in the middle and lower troposphere is investigated and the structure feature and the possible physical mechanisms of it are presented. The results shows that the motion track of the vortex is well coincident with the rainfall variation at the center of rain masses as well as the evolutions of rain intensity and the vortex intensity. Stream ascended strongly in the center of the mesoscale vortex and the structure of lower-level convergence and upper-level divergence are very favorable to the generation and development of the mesoscale convective system. The interaction of the positive isobaric moist potential vorticity disturbance at low and upper level is a possible mechanism of the genesis and development of mesoscale vortex. Strongly strengthening of the low level jet and releasing of the latent heat of condensation have effect on the occurrance of the disturbance of the moist potential vorticity in low lever, which is important conditions to the genesis and development of mesoscale vortex.