Interannual Variability of Summer Rainfall over the Northern Part of China and the Related Circulation Features

In this study, interannual variability of summer rainfall over the northern part of China (NPC) and associated circulation patterns were investigated by using long-term (1961-2013) observational and reanalysis data. Two important NPC rainfall modes were identified by empirical orthogonal function analysis: the first is characterized by an almost uniformly distributed rainfall anomaly over most parts of the NPC, while the second shows rainfall variability in Northeast China (NEC) and its out-of-phase relationship with that in North China (NC) and the northern part of Northwest China. The results also suggest that the NPC summer rainfall anomalies are also closely associated with those in some other parts of China. It is revealed that the circumglobal teleconnection pattern associated with the anomalous Indian summer monsoon (ISM) and the Polar/Eurasia (PEA) pattern work in concert to constitute the typical circulation pattern of the first rainfall mode. The cooperative engagement of the anomalous ISM circulation and the PEA pattern is fundamental in transporting water vapor to the NPC. The study emphasizes that the PEA pattern is essential for the water vapor transport to the NPC through the anomalous midlatitude westerly. In the second NPC rainfall mode, the typical circulation pattern is characterized by the anomalous surface Okhotsk high and the attendant lower tropospheric circulation anomaly over NEC. The circulation anomaly over NEC leads to a redistribution of water vapor fluxes over the NPC and constitutes an out-of-phase relationship between the rainfall anomalies over NEC and NC.