Out-of-Phase Decadal Change in Drought Over Northeast China Between Early Spring and Late Summer Around 2000 and Its Linkage to the Atlantic Sea Surface Temperature

摘要

Based on the standardized precipitation evaporation index (SPEI) and empirical orthogonal function (EOF) analysis, this article presents that the primary mode (i.e., a monosign pattern) of drought over Northeast China (NEC) in early spring (February-March-April, FMA) and late summer (July-August-September, JAS) shows an out-of-phase decadal change, which is characterized with a wetting polarity in FMA while a drying polarity in JAS approximately after 2000 as compared to the counterparts before that time. Such an out-of-phase decadal change is generally supported by the decadal changes in atmospheric circulations. Compared to the former period, during the latter period, the equivalent barotropic cyclonic (anticyclonic) anomalies dominate northeastern Asia and an anomalous ascending occupies NEC in FMA (JAS), which help to alleviate (aggravate) drought over NEC. In addition, decreases in water vapor transport toward the NEC region act in the aggravation of drought in JAS, while the variation of drought in FMA is not closely connected to the change in water vapor transport. Further analyses indicate that the shifts of the sea surface temperature (SST) in the tropical and mid-high latitude Atlantic Ocean from a cold phase to a warm phase also play a role in the decadal change of drought in FMA and JAS, respectively, through their influences on the above atmospheric circulations with the aid of downstream propagation of wave trains. Hence, the seasonal dependence of the Atlantic SST and atmospheric circulations contributes to the out-of-phase decadal change of drought in NEC.