Probability Distribution And Circulation Background Of Heavy Rainfall In South China

By using daily precipitation over South China and the NCEP/NCAR reanalysis data of SLP in Southern Hemisphere during 1960～2008, the probability distributions of precipitation extremes during raining season in South China are investigated by means of statistical method ,for example ,Le Page, GEV(general extreme value) and so on. The influences of the Southern Hemisphere circulation and vapor transport on the heavy rainfalls are also analyzed. The large-scale circulation, vapor transport and closed relation circulation background of the Southern Hemisphere about continuous heavy rainfall processes over South china from May to June in 2008 are studied. Some results are received as follows:(1) Precipitation intensity in the first raining season is stronger than the second raining season. Precipitation in the first raining season concentrats on inland and that concentrats on inshore in the second raining season. An abrupt change of precipitation trend in South China occurred around 1992, from a descendent trend to an ascending trend. After the abrupt change the extremes precipitation and the daily maximum precipitation both are weak in the first raining season and that both are strong in the second raining season.(2) The spatial distributions of the daily maximum precipitation and the heavy precipitation days are all similar, ie, in the first raining season with a pattern of"negative～positive～negative"from south to north and with a pattern of"positive～negative"from south to north in the second raining season. Spatial distributions of variation of the daily maximum precipitation are agreement with the heavy precipitation days.(3) On the interdecadal time scale, when the Australian and the Mascarene high in Southern Hemisphere are stronger, extremes precipitation would be less than normal in the first raining season and more than normal in the second raining season.There are three water vapor source for South China,ie, the Bay of Bengal , the South China Sea and the Western Pacific Ocean.(4) The four heavy rainfall processes experience a various process of"weak～stronger～the strongest～weak". The Western Pacific Ocean subtropical High is stronger and shifts both to south and to west during heavy rainfall periods and Sea of Okhotsk appears the blocking high.Vapor transportation of the Somali jet,the Bay of Bengal and the South China Sea are all stronger and vapor characteristics are different during the four heavy rainfall processes. The four heavy rainfall processes have closed relationship with the intensities of cross-equatorial flows and the Australian and the Mascarene high in Southern Hemisphere. Anomalous convection enhancement of the Somali jet is one of the main reasons in the formation of lasting-several-day heavy rainfall. So anomalously active of the prior Australian and Mascarene high and prior cross-equatorial flows are premonitory for heavy rainfall.