Characteristics of Interannual Variability of Summer Rainfall in North China

Based on the 160-station precipitation observations in China from 1951 to 2000 and ERA-40 reanalysis data from 1958 to 2002,the persistent summer drought in North China and its corresponding circulation anomalies are analyzed.Results show that the summer rainfall obviously decreased and durative drought occurred in North China since the mid and late 1970s.The warm high in mid and low tropospheres over North China,the high pressure ridge over Okhotsk Sea and the subtropical high in the western Pacific are the major circulation system influencing summer climate anomaly in North China.When summer rainfall in North China decreases,the anticyclonic anomaly circulation at 700hPa and the northerly wind anomaly obviously appear over North China,in such a way that the descent flow strengthens,the water vapor divergence appears,and East Asian westerly jet at 200hPa moves further south and decreases,and vice versa.