Interannual Variation Characteristics And Mechanism Of Precipitation Concentration Period In Southern China

Based on daily precipitation data of 918 stations in southern China from 1961 to 2012 provided by National Meteorological Information Center of China,NCEP/NCAR reanalysis data and Hadley center sea surface temperature data,a new method for calculating the Precipitation Concentration Period (PCP) was defined. As a result,the PCP in South China and the Yangtze-Huaihe River region were recognized,and then the interannual variability was analyzed for these two types of PCP respectively, and the possible mechanism was analyzed through the analysis of typical drought-flood years' characteristics and generalized equilibrium feedback assessment (GEFA). The results are as followed:(1) The climatic PCP of South China is from April 8th to June 28th, basically corresponding to the pre-flood season in South China, and in this period, a lot of water vapor was transported into this area resulted from the low pressure tank in the Bay of Bangle and Western Pacific Subtropical High (WPSH); The PCP in the Yangtze-Huaihe River region is from June 9th to July 13th, basically corresponding to the Meiyu period, and in this period, lots of water vapor was delivered into this area by the the southwest airflow produced by the airflow changed from the front side of the anticyclonic circulation on the Indian Ocean accompanied by the south airflow on the west side of WPSH.(2) The characteristics of the circulation anomalies between typical flood and drought years in South China and the Yangtze-Huaihe River region during the PCP were found to be: In South China,during PCP,the East Asia trough is remarkable in 500hPa geopotential height field, and the WPSH is stronger than normal; There is a strong anti-cyclonic anomaly circulation over tropical western Pacific in the 850hPa wind anomaly field; In 200hPa zonal wind field, there is a positive exception over South China,i.e., the East Asia Subtropical Westerly Jet is significantly enhanced,above which are all conducive to the increase of precipitation in South China. In the Yangtze-Huaihe River region, during PCP,there is a distribution of "west-high &east-low" in Eurasian high latitude area,and there is a distribution of“+-+" in East Asia and its coastal areas from low latitudes to middle-high latitudes in 500hPa geopotential height field; In 850hPa wind field, the vicinity of the Philippines is controlled by abnormal anti-cyclones, resulting in a type of EAP teleconnection in East Asia coast and its nearby areas, which leads to an abnormal wind field convergence in the Yangtze River Basin; The East Asia Subtropical Westerly Jet in 200hPa zonal wind field is significantly enhanced, which is favorable for the increase of rainfall in the Yangtze-Huaihe River region.(3) The analysis results about the distribution of sea surface temperature in formal and same period of two types of PCP are: The interannual variability of PCP in South China is mainly affected by attenuated mixed-type El Nifo, which influence the concentration of precipitation in South China by stimulating the anomalous anticyclone in the vicinity of the Philippines, while the interannual variability of PCP in the Yangtze-Huaihe River region is affected by decay process of eastern-type El Nino, the consistent warmer Indian Ocean and the North Atlantic SST Tripod, which influence the concentration of precipitation in Yangtze-Huaihe River region by stimulating the anomalous anticyclone in the vicinity of the Philippines and related EAP type height field abnormity. This has a good indication for short-term climate prediction. The results of GEFA diagnosis show that the PCP in southern China is mainly due to the effect of El Nino Modoki mode in central; The PCP in Yangtze-Huaihe River region is mainly affected by the "three-pole" SST mode in North Atlantic and the uniform warm mode of the tropical Indian Ocean which is stimulated by El Nino.