Differences of oceanic and atmospheric circulation features among the rainfall band patterns in summer in eastern China

Three indices are defined to represent the characteristics of rain band patterns in summer in eastern China and the differences of ocean and atmospheric circulation features among the three rainfall band patterns are analyzed in terms of the East Asian circulation, moisture transport and sea surface temperature (SST) by using the NCEP/NCAR reanalysis data, the UKMO HADISST1 global monthly SST data and the monthly precipitation data of 120 stations in eastern China during 1950—2009. The results show that : (1) The differences of the ocean climatic background among the three rainfall band patterns are as fellows: pattern Ⅰ in which the rainy belt is located in the northern part of China corresponds to a pattern of positive SST anomalies in the North Pacific, negative SST anomalies in the warm pool and the warm currents over eastern Australian and positive SST anomalies in the westerly drift region over the South Pacific; pattern Ⅱ in which the rainy belt is located between the Huanghe River and Huaihe River regions corresponds a pattern opposite to pattern Ⅰ and pattern Ⅲ in which the rainy belt is located in the area south of the Yangtze River corresponds to a pattern of the SST anomaly distribution in the North Pacific consistent with that in pattern Ⅰ. (2) The differences of characteristics of circulations and water vapor transports among the three rainfall band patterns are as fellows: the characteristics of pattern Ⅲ are almost opposite to pattern Ⅰ； when pattern Ⅲ appeared in the eastern China, the strongest blocking appeared in the middle and high latitudes of East Asia, the latitudinal circulation anomaly was stronger and the subtropical high over the western North Pacific was obviously stronger with its position more southward and westward than normal; meanwhile, anticyclonic anomalies circulations appeared in the western North Pacific and the latitudinal water vapor transport was strengthened in the area. The above characteristics are opposite when pattern Ⅰappeared. The characteristics of pattern Ⅱ are close to pattern Ⅰ and the differences between these two appeared in the subtropical area over the western North Pacific. When pattern Ⅱ occurred the anticyclonic anomalies circulation appeared in the area while when pattern Ⅰ occurred the cyclonic one appeared in the area. (3) SST anomalies in the equatorial central and eastern Pacific and the westerly drift region of the South Pacific in winter are premonitory signals for forecasting the subtropical high over the western North Pacific in summer.