The Possible Mechanism of a Type of Vortex Heavy Rainfall during the Pre-Rainy Season in South China

In this paper, NCEP reanalysis data, intensive observation data collected from field experiment, model simulation data, and topographic trial data are fully analyzed to study a severe heavy rainfall event during 5?6 June 2008 in South China. Unlike most warm region rainfall cases, this one is associated with an obvious vortex system, which draws in water vapor and energy from the southwest monsoon surges ahead of a low trough above the Bengal Bay (BLT, Bengal Low Trough). At the lower troposphere, three currents, especially the southwest current and the east current, converge into the southeast of the vortex. Thus, the distributions of strong vorticity, water vapor, and ascending motion cause frequently occurrence and growth of convection there. The possible reasons for this rainfall event are summarized as a conceptual model.