Characteristics Of The Mesoscale Convective Systems Over South China During Warm Seasons

Located in the southern section of the mainland of China and deeply affected by the monsoon, South China is an area with the longest the flood season and is among the areas which have the most precipitation in China, having relatively frequent convective activities. In this paper, based on the hourly infrared brightness temperature(TBB) (equivalent temperature of black body) dataset gathered by the geostationary satellite Fengyun 2nd between 2005 to 2010, temporal and spatial distributions and features of the MCSs (mesoscale convective systems) in worm season over South China were investigated, furthermore, large-scale environmental characteristics during MCS' activity which consists of four period, i.e. preexisting period, initiating period, maximum period and the ending or fading period, were analyzed through the dynamic synthesis approach together with NCEP 1°×1°reanalysis data. The research shows that:(1) MCSs' spatial and temporal distribution in South China reveals that:the coastal area of Guangxi-Guangdong and Hainan island is the active-MCS area, while MCSs occur infrequently in the north inland, with a less than 4% occuring frequency over north of 24°N; there are a noticeable monthly variation characteristics of MCSs and a progress of convective activities northing and strengthening gradually, which come to a maximum in June, while it becomes weak and begins to retreat southward in July; MCS daily variation over South China appears to be a bimodal distribution, while the MCS emerging summit, attaining a mature summit or fading summit appearing between afternoon and evening, however, a secondary peak respectively including emerging, thriving and disappearing process turn out in the next morning;(2) the average lifespan of MSC is 4.6 hours, with 91.1% of them having a lifespan between 3 and 7 hours and a 25.6 km per hour average speed, which go eastward in most case while it also may go westward or southward in few cases;(3)the characteristics large-scale environment field in which the MSC of South China occurred can be mainly summerized as follows:in the upper troposphere, MCS is controled by anticyclone at the east of the South Asian high, westerly jet exists on the north of the MCS, while above the MCS there is a strong anti-cyclonic divergence; MCS is formed in the westerly trough of the northwest side of the West Pacific Subtropical High, and neutral condition emerge within some parts of the cloud clusters with unstable stratification reaching to 650hPa; in the lower troposphere there is uniform southwest wind with small baroclinic; in the low-level, southwesterly jet sent water vapor to South China, while on the left of the jet(where the MCS happens) there forms a vortex, at which place there is a large accumulation of water vapor.(4) The basic properties of convective clouds has little difference from the average in other six years; large jet stream in 2008 is stronger than the average, with the strong wind center moving westward obviously and meridional circulation becoming stronger;the West Pacific Subtropical High is located more northward and more eastward, vertical motion is abnormally active, while at the places where MCS appears the vortex is clearer and stronger than usual, vapor convergence being stronger.