Diagnostic Analysis of a Heavy Rainfall in Southern Sichuan of China Induced by Southwest Vortex

Using NCEP data of 1°×1°with 6-hour interval, the evolution of Southwest Vortex (SW) causing heavy rainfall in Southern Sichuan of China during 8-10 July 2007 is comprehensive diagnosis. The results indicate that: (1) On height field, there is a small groove on 500hPa, and 700hPa southwest vortex moving eastward slowly; on fow field; there is a structure of convergence on the low level and divergence on the upper level; on vertical velocity field, there maintains a relatively strong upward motion, they provide a favorable circulation background for the development and maintenance of heavy rainfall. (2) On the lower troposphere, the pseudo-equivalent temperature decreases with height. The existence of an unstable energy can easily trigger heavy rainfall. (3) Moist potential vorticity analysis gives a superposition of the vertical structure of the configuration, both positive and negative, to provide a favorable situation in the development of heavy rainfall. Strong precipitation areas are basically located in the dense band contour of the positive and negative junction of MPV1; the increase of MPV2 is conducive to the intensification of convection and rain.