Persistent Extreme Precipitation In East China, Its Related Low-frequency Oscillation Circulation And Sea Surface Temperatures

Based on daily rainfall data in china from April to October during 1961-2010, Using the Butterworth bandpass filtering method, the low frequency oscillation of rainfall in China is analyzed. Through identifying regional persistent extreme precipitation events(PEPEs), the connection between PEPEs and the low frequency oscillation of rainfall are discussed. Then by using NOAA Extended Reconstructed Sea Surface Temperature(SST), NCEP/NCAR reanalysis dataset and OLR data, the tropical northwestern Pacific SST condition and its possible connection to PEPEs and low frequency rainfall in East China are also investigated.The results show that the low frequency oscillation rainfall is most active over southeastern China. The maximum contribution of 10-50-day oscillation rainfall reaches 40% in some years and the average contribution is 24%. The PEPEs occurs frequently in June, July and August.20-50-day oscillation rainfall is more active over the Yangtze-Huaihe River Basin(YHR) and in the region south of the Yangtze River(SYR) accompanied with PEPEs. In the PEPEs years over the YHR and SYR, the summer tropical northwestern Pacific SST exhibits positive anomalies. The positive SST anomalies likely enhance 20-50-day oscillation rainfall and increase the possibility of PEPEs occurrence over YHR and SYR.In the tropical northwestern Pacific SST warm anomalies years, subtropical high in the western Pacific is more powerful and associated with a westward shift. The 20-50-day oscillation of subtropical high in the western Pacific and the East Asian Trough are more active. During the active period of 20-50-day oscillation rainfall over YHR and SYR, in the low and middle troposphere a strong low frequency cyclonic circulation is located over YHR and SYR, while a strong low frequency anticyclone is over South China Sea. Anomalously warm/moist air taken by low frequency anticyclone from South China Sea encounters anomalously cold/dry air taken by low frequency cyclone from mid-high latitudes. Moreover, in the upper troposphere, the 20-50-day oscillation of jet which favors robust divergences for rainfall over YHR and SYR is more active. During the active period of 20-50-day oscillation rainfall over YHR, a strong low frequency anticyclone over YHR provides a good condition for rainfall.