中文摘要：

利用1951—2000年中国160个台站降水资料和1958—2002年欧洲中心的ERA-40再分析资料,分析了华北地区夏季降水和对应大气环流的变化特征。结果表明：华北地区夏季降水自20世纪70年代中后期开始明显减少,出现持续性干旱;华北地区上空的暖高压、鄂霍次克海地区的高压脊和西太平洋副热带高压是控制华北地区的主要环流系统。当华北地区降水偏少时,华北地区上空700hPa出现反气旋型环流异常,华北地区上空出现明显偏北风异常,且下沉气流加强,水汽出现辐散,200hPa高度上西风带偏南且减弱;反之,当华北地区降水偏多时,华北地区上空700hPa出现气旋型环流异常,并出现偏南风异常,上升气流加强,水汽输送辐合,200hPa上西风异常偏北加强。

英文摘要：

Based on the 160-station precipitation observations in China from 1951 to 2000 and ERA40 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 700 hPa 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 200 hPa moves further south and decreases, and vice versa