Research On The Formation Mechanism Of Different Types Warm Area Heavy Rainfall In Southern China

First, make a statistic analysis on the the three types of warm sector heavy rain by using1°x1°NCEP FNL analysis data in May2005, May2008and June2008. Analysis found that, under the favorable situation in guangxi coastal easy into the low vortex, but heavy rain belt area often generated in the east of the low vortex, this type accounted for83%of the total, and in most cases composed of frontal rain belt with low vortex-double stretching. So using live data and WRF mesoscale numerical model with a low vortex occurred most double belt in south China heavy rain (Type II, III) process area are simulated and diagnostic analysis.The research results of the Type II warm area heavy rain shows that:as the front moves towards south, a vortex is generated in Guangxi coastal aera, which is located in the southwest of the front. As a source of potential vorticity, this vortex performs stability in the mid-high levels, providing positive potential vorticity for frontal rainband and warm sector rainband respectively, and showing that the frontal rainband has an important influence on the form of warm sector rainbelt. The main effects of southern rainband to northern are mainly at middle levels, near112°E-114°E. large-value potential vorticity in southern rainband tranports towards north, which is leading to the connection of these two rainbands here.At the same time, northern upper-level trough also transports large-value potential vorticity to the northern rain belt to maintain it. This study also founds significant structure differences between warm area rainstorm and frontal rainstorm, and the structure is identified by frontal rainband and traditional rainband. The pattern in favor of warm area rainfall is mainly at mid-high levels, warm area rainband has the structure of three-layers with different properties.this structure is conducive to the maintenance and increase of the precipitation.The results of the type Ⅲ of heavy rain study is close to type II, but is good for heavy rain a vortex distribution area mainly displays in the upper and lower, middle performance is not obvious. In the lower,great value in the center of the vortex to the spread of warm zone stretching mainly in west of114°E, Middle, near low vortex the potential vorticity is mainly to the frontal rain belt conveyor, At the top have a potential vorticity come from the upper trough spreat to the north, near the low vortex the potential vorticity spreat to warmer areas.RIP particle trajectory model also demonstrates that the potential vorticity transmission source in the particle movements is the vortex located Guangxi coastal area, potential vorticity conveying height is different. Type II heavy rain related to frontal rain belt in the area of a vortex mainly come from the top of the upper trough, middle-level southwest vortex circulation in guangxi; Associated with heavy rain rain belt area of potential vorticity, part of the middle guangxi coastal low vortex, the other part by sea. potential vorticity of Type III heavy rain frontal rain belt mainly comes from the upper trough and low-level south belt conveyor;Warm area stretching potential vorticity mainly comes from the high and lower in southern guangxi low vortex and large value a vortex offshore. showing that this potential vorticity source plays an important role on the form of these two rainbands.Two storm rainfall in south China in the850hPa height, frontal rain belt corresponds to the horizontal vorticity measurement value is greater than the warm area in China. Frontal rain belt in the negative horizontal vorticity component ζx area,precipitation center corresponds to a negative value; Both type Ⅱ and type Ⅲ warm precipitation most of the time zone there is a positive ζx area in southern area. Warm rains area located in the junction of positive and negative, conducive to the upward movement development; The middle-high level ζx>0, Due to the smaller values of the lower horizontal vorticity, updraft in high-level performance significantly. Visible, the vertical circulation due to the horizontal vorticity of is an important factor to produce heavy rains.