Analysis On Torrential Rain In South China Caused By Tropical Disturbance

Torrential rain in South China caused by tropical disturbance is caused by the interactions between tropical disturbance (TD) which is manifested as a mesoscale vorticity accompanied with mesosacle convective cloud clusters and Western Pacific Subtropical High (WPSH) or other high pressure weather system. Torrential rain in South China caused by tropical disturbance is manifested as a mesoscale vorticity in lower troposphere in Northern South China Sea and Beibu gulf accompanied with low-level jet (LLJ) and mesosacle convective cloud clusters. This kind of torrential rain which happens either in the first rainy season or autumn and lasts 2-3 days or more has the characteristic of long duration. Additionally, its large precipitation intensity with hourly rainfall exceeding 100mm/h and centralizing precipitation location represents the obvious mesoscale characteristics. Apparently, serious casualties and economic loss might be brought by the torrential rain.Mechanism of this kind of torrential rain was studied through the torrential rain process in western Guangdong Provence from 22th to 24th May in 2009 and that in Hainan Provence from 1th to 8th October 2010, using conventional observation data, unconventional observation data and the averaged fields of GFS (Global Forecast System) 0.5°×0.5°analysis data. The results suggested that double positive feedback mechanisms were formed by the interactions between the TD and WPSH (or other high pressure weather system). Firstly, increased pressure gradient induced by the interactions between WPSH and TD accelerated wind in the adjacent area, which is helpful to the formation and enhancement of LLJ. The enhancement of LLJ reinforced the barotropic instability, which is favorable to the development of tropical vorticity disturbance. Secondly, the first positive feedback is useful to increase the convergence on the LLJ. The velocity disturbance on the LLJ also helps tropical cloud clusters develop on and above the LLJ, which is beneficial to the enhancement of LLJ. Eventually, heavy rainfall with long duration formed.Mesoscale characteristics and mechanism of the extreme torrential rain process in western Guangdong Provence on 08:00 to 12:00 May 23th in 2009 was analyzed by conventional, unconventional observed data. We found that short-time strong rainfall was brought by a mesoscale convective complex on the north end of the monsoon through. Two band mesoscale convective systems which generated south to western Guangdong Provence reinforced while landed on the area from Yangjiang to Taishan. Mesoscale convective cells developing rapidly while moved across Yangjiang and Taishan from the south to north leaded to the extreme precipitation. Weather Research and Forecasting (WRF) Model numerical simulation results and diagnostic analysis results showed that with atmosphere with high relative humidity in troposphere and week convective instability in lower troposphere, convergence in the boundary layer brought by east wind, northeast wind and southwest wind jointed with convergence on the LLJ brought by interactions between TD, WPSH and LLJ intrigued and maintained the deep convection. At the same time, wind convergence in the boundary layer was also of great help to the deep convection formation in the extreme torrential rain process in Qionghai in Hainan Provence on 13:00 to 23:00 October 5th in 2010.