Footprints of Pacific Decadal Oscillation in the interdecadal variation of Consecutive Cloudy–Rainy Events in Southern China

Abstract

Consecutive Cloudy-Rainy Events (CCREs) in spring have a disastrous impact on agriculture and the natural ecosystem over southern China. In this study, the variability of the frequency of spring CCREs in southern China from 1961 to 2016 and the underlying mechanism of these phenomena are explored. The results indicate that the dominant mode of the CCRE frequency in southern China varies in a uniform spatial pattern, and the time series exhibits a strong interdecadal variation, with a higher frequency between the late 1970s and late 1990s and a lower frequency in the other periods. Such an interdecadal variation in the CCRE frequency varies well in–phase with the Pacific Decadal Oscillation (PDO). Further dynamic diagnosis and numerical simulation both suggest that the PDO is linked with CCREs in southern China through two physical processes. On the one hand, the anomalous PDO is associated with the anomalous North Pacific Oscillation (NPO). The westward extension of the NPO is accompanied by anomalous East Asian westerly jet (EAWJ) and West Pacific subtropical high (WPSH). On the other hand, the eastward development process associated with the PDO variation can excite a Rossby wave train over the Northern Hemispheric mid-latitudes. The PDO-related Rossby wave train can alter East Asian atmospheric circulations, leading to anomalous EAWJ. The changes in the EAWJ and WPSH can further lead to anomalous upward motion over southern China and moisture transportation from the South China Sea to southern China. Through these physical processes, the positive–phase (negative–phase) PDO provides a favorable (unfavorable) condition for the occurrence of CCREs in southern China.