Indian Ocean Dipole and ENSO’s mechanistic importance in modulating the ensuing-summer precipitation over Eastern China

Abstract

AbstractEastern China was extremely wet in summer 2020, which is found to be related to the potential delayed effects of the Indian Ocean Dipole (IOD). Additional knowledge is warranted to improve our understanding of detailed mechanisms of such an effect. In this study, we compared physical processes associated with delayed effects of the IOD and El Niño–Southern Oscillation (ENSO) on summer precipitation. Partial correlation and composite analysis reveal that ENSO modulates precipitation mainly over the Yangtze River Valley, whereas IOD benefits precipitation farther north. Both IOD and ENSO can stimulate anticyclonic circulation over the western North Pacific (WNP) in the ensuing summer but with different spatial distributions related to the different sea surface temperature (SST) evolution processes. IOD is similarly followed by warming signals in the Indian Ocean, known as the “capacitor” effect, but the location is closer to Australia than that associated with ENSO. IOD also stimulates significant SST cooling anomalies over the equatorial Pacific during the ensuing summer, jointly contributing to the anomalous anticyclone over WNP. Numerical experiments confirm that combined effects of the Indian Ocean “capacitor” and equatorial Pacific cooling can generate an anomalous anticyclone with wider distribution in the meridional direction over WNP.