Arctic dipole anomaly and summer rainfall in Northeast China

A dipole structure anomaly in summer Arctic atmospheric variability is identified in this study, which is characterized by the second mode of empirical orthogonal function (EOF) analysis of summer monthly mean sea level pressure (SLP) north of 70°N, accounting for 12.94% of the variance. The dipole anomaly shows a quasi-barotropic structure with opposite anomalous centers over the Canadian Arctic and the Beaufort Sea and between the Kara Sea and the Laptev Sea. The dipole anomaly reflects alternating variations in location of the polar vortex between the western and eastern Arctic regions. The positive phase of the dipole anomaly corresponds to the center of the polar vortex over the western Arctic, leading to an increase in summer mean rainfall in Northeast China. The dipole anomaly has a predominant 6-year periodicity, and shows interdecadal variations in recent decades. Supported by the National Key Basic Research and Development Project of China (Grant No. 2004CB418300), the National Basic Research Program of China (973 Program) (Grant No. 2007CB411505), Chinese COPES project (GYHY200706005) and the National Natural Science Foundation of China (Grant No. 40475030). R. D’Arrigo acknowledges support from the National Science Foundation (Grant No. OCE 04-02474), Lamont-Doherty Earth Observatory Contrib. No. 7126