资源环境科技发展态势分析平台

“West China Autumn Rain” (WCAR), as the last rainy season in China, is inclined to flooding and secondary disasters which often cause severe damages to the development of socio-economy and safety of people's lives. It is thus crucial to explore influential factors and associated physical processes for the anomalies in WCAR. In this study, based on the gridded precipitation data and reanalysis data during 1961–2013, we presented that the WCAR-AO relationship has strengthened in the mid-1980s, which varies from an insignificant correlation to a significant positive one. During the latter period (the significant period), the positive AO phase corresponds to a strong anticyclonic circulation anomaly over the region from northeast Asia extending to the North Pacific in the middle and lower troposphere, concurrent with a northward displacement of the East Asian jet (EAJ) in the upper troposphere. These atmospheric circulation situations favor the increase of WCAR, through their influences on the moisture and dynamical conditions. During the former period (the insignificant period), however, the association of the AO with above atmospheric circulations is weakened, thus diluting the WCAR-AO linkage. The unstable relationship between the AO and aforementioned atmospheric circulations may be due to the change in the AO structure. In the latter period, associated with the positive AO phase is a typical seesaw pattern featured by negative sea level pressure (SLP) anomalies in the Arctic and positive SLP anomalies in the North Atlantic and the North Pacific, whereas the anomalous center in the North Pacific becomes less pronounced in the former period. This discrepancy may be attributed to stronger wave activity arising from the SST warming from the former period to the latter period over the North Pacific.