Analysis on circulation characters of persistent heavy rain in the first flood season in South China

Based on the daily precipitation data from 279 stations in South China and NCEP daily reanalysis datasets, this paper analyzed 82persistent heavy rain events in the first flood season of South China from 1961 to 2008. The results indicate that the persistent heavy rain lasted for 3-5 days predominates all the events, occurred mainly from the end of May to June, and happened 1.71 times annually. According to main low pressure systems at 500 hPa around South China, 82 persistent heavy rain events in the first flood season are divided into five types,namely the East Asia bottom-trough-type (EAT), the low trough over South China-type (TSC), the prior-trough over the Bay of Bengal-type(TBB), the fluctuation in westerly belt-type (FWB), and landing tropical storms-type (LTS) respectively. Among them, the occurrence frequency of EAT is the most but that of LTS is the least; the mean duration of TBB is the longest but that of FWB is the shortest. The mean intensity of subtropical high over the Western Pacific is high in all types, and South China is influenced either by low vortex or trough directly or by southwest airflow mainly. The main rainfall centers of all types drop in Guangdong Province, but an obvious rainfall center of TBB appears in Fujian Province also. The duration of all types is controlled by both relative cold sector and cold advection in the Yangtze-Huaihe River region at 850hPa, but is mainly influenced by warm advection in the area of South China. For warm advection at 850 hPa influencing South China, TSC is the strongest, followed by FWB and TBB, and EAT and LTB are the weakest. In all types water vapor convergence zone integrated from surface to 300 hPa is situated in South China, and among them water vapor convergence zone is obvious in LST, TSC and TBB. The order of the large precipitable water (PW) center values in the coastal areas of South China from big to small is LTS, EAT, TBB, FWB and TSC.