Numerical Simulation And Statistic Analysis On The Formation System Of Warm Sector Heavy Rainfall In May And June From 2000 To 2009

The primary datasets used in this study include the NCEP 1°×1°reanalysis data and 77 south China meteorological stations conventional surface data. A statistical analysis on the features of the circulation under 500hPa and classification on the formation system of warm sector heavy rainfall in South China in May and June from 2005 to 2008 are performed. The formation system of warm sector heavy rainfall in South China is divided into three types:shear line type, low vortex type and southerly wind velocity shear type. The paper mainly comparatively analyzes the characteristics of various types of warm sector heavy rainfall before and after the onset of South China Sea (SCS) summer monsoon, and finally makes a numerical simulation on a typical case of warm sector heavy rainfall. The conclusions are as follows:The proportion of shear line type, low vortex type and southerly wind velocity shear type of the warm sector heavy rainfall is 39%,15% and 46% respectively. Either before or after the onset of the SCS summer monsoon, southerly wind velocity shear type has the largest frequency.Different types of warm sector heavy rainfall have significant differences around the SCS summer monsoon. Warm sector heavy rainfall mostly happens after the monsoon onset. Before the outbreak of the monsoon, the shear line type, in which cold shear line class is the main class, is mainly affected by the southern branch trough. And the low vortex type mostly takes place in the south and southwest of the vortex where is near the cold shear vortex line, and it is mainly affected by the divided trough of southern branch trough, while southerly wind velocity shear type is easily affected by the plateau trough. After the outbreak of the monsoon, warm shear line class is the main class in the shear line type, which is often affected by the divided trough of plateau trough. And low vortex-type, of which warm shear vortex is main class, mainly happens in the northeast to the southeast of the vortex, and is often affected by plateau trough, the divided trough of plateau trough and the divided trough of southern branch trough, and it's the same as southerly wind velocity shear type.The composite analysis of warm sector heavy rainfall shows that, the features of the circulation of warm sector heavy rainfall in South China have similarities and differences as follows:the similarities are that, subtropical high ridge is about 6-8 latitude distance to the rainfall, and it's the important circumstance of warm sector heavy rainfall, and the southwest air flow, which flows into the system northward along the west side of the subtropical; high; bring plenty of warm & moist air conditions for the storm. Warm sector heavy rainfall in South China is caused by the configuration of low level convergence and upper level divergence. Convergence in 500 hPa is weak. The differences are that, different types of warm sector heavy rainfall correspond to different 500 hPa trough characteristics. The shear line type (especially cold shear line class) often corresponds to large-scale deep trough in the north, and low vortex type is the most lose to the westerly short-wave trough, while both warm shear line class and southerly wind velocity shear type, whose convergence centers are lower than others, are far from the 500 hPa trough. Cold shear line class and vortex cold line class has the strongest cold air behind the trough.As the southerly wind velocity shear type has the largest frequency in south china, for more the detail of the internal mechanism and formation mechanism of the rainfall, we used WRF mesoscale model to simulate a warm sector heavy rainfall in June 2008, and found that:the westerly short-wave trough, the West Pacific Subtropical high ridge line's westward extension, the SAH and high level jets had effect on the development of storm. TBB convective clouds' activities had a direct impact to the rain. The rainfall was in the warm conveyor belt which was in the south of the vortex. Low-level southerly wind component is an important factor in the increase of rainfall. Water vapor mainly came from two sources:the SCS and Indochina. The CAPE in the rain area of Guangdong reached 1000J/kg, which was conducive to rainfall. The negative MPV center corresponded to the storm, and unstable energy from the low level had significant effect on the rainfall.