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

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.