东亚夏季风年际变率及其与中、高纬度大气环流以及外强迫异常的联系

Interannual variability of the East Asian summer monsoon and its association with the anomalous atmospheric circulation over the mid-high latitudes and external forcing

利用欧洲中心35年(1968—2002年)月平均再分析资料(ERA-40),通过矢量经验正交分析方法,研究了东亚夏季风年际变率的第2、3优势模态及其与中、高纬度大气环流和外强迫异常之间的联系。这两个优势模态均与北半球中、高纬度大气环流异常有密切的关系,累计解释协方差超过了东亚夏季风的第1模态。东亚夏季风变率的第2模态解释了13%的风场协方差,由两个不同的子模态构成(P21和P22),分别对应夏季500hPa高度场的双阻塞高压异常型(乌拉尔山附近以东和鄂霍次克海阻塞高压异常)和欧亚大陆北部的准纬向遥相关波列。东亚夏季风第3模态解释了8.2%的风场协方差,依然包括两个不同的子模态(P31和P32),分别对应夏季500 hPa高度场在欧亚大陆北部的两个不同遥相关波列。这些夏季风模态均对中国降水变化产生影响,特别是在华北和东北地区。近几十年来中国夏季降水的两次年代际变化与夏季风第3模态的关系可能更为密切。春季北极海冰对于中国夏季降水变化和夏季风模态P31均是先兆因子。

Using the ERA-40 data（1968-2002）.this study investigated the second and third dominant modes of the East Asian summer monsoon（EASM）variability and their associations with the atmospheric circulation and external forcing in the boreal mid-high latitudes by means of the complex vector empirical orthogonal function method.Both the second and third dominant modes are closely related to atmospheric circulation anomalies in the boreal mid-high latitudes,and their accumulative covariance exceeds the leading mode of the EASM variability.The second mode accounts for 13%of the covariance.and contains two different sub-modes（P21 and P22）.They correspond respectively to the anomalous dual-blocking high pattern（the Ural Mountains and the Okhotsk Sea）and the northern Eurasian teleconnection pattern.The third mode accounts for 8.2%of the covariance,and contains also two sub-modes（P31 and P32）,which correspond respectively to the two Eurasian teleconnection patterns.These EASM modes affect Chinese summer rainfall variation,particularly in north and northeast China.In recent decades,the two decadal variations of Chinese summer rainfall may have a closer relationship with the third mode relative to the second mode.The spring Arctic sea ice might provide a precursor for both Chinese summer rainfall and the summer monsoon mode P31.