Synergistic effect of El Nino Southern oscillation and subtropical Indian Ocean Dipole on Southern China winter precipitation

Both the El Nin & SIM;o Southern Oscillation (ENSO) and subtropical Indian Ocean Dipole (SIOD) have significant impacts on the winter precipitation over southern China (SC). In this study, we investigate the synergistic effect of ENSO and SIOD on southern China winter precipitation (SCWP). Our findings indicate that SCWP is closely associated with the out-of-phase configurations of ENSO and SIOD, with precipitation tending to increase (decrease) during El Nin & SIM;o and negative SIOD (La Nin & SIM;a and positive SIOD). During El Nin & SIM;o and negative SIOD, the El Nin & SIM;o leads to an anomalous anticyclone over the northwest Pacific through Walker circulation and Gill-type tropical response. The associated southwesterly winds of the anticyclone transport ample water vapor towards SC. The El Nin & SIM;o and negative SIOD both trigger a wave-like pattern from Europe to SC. This wave train (PC1-like wave train) propagates towards SC and induces anomalous cyclonic circulation and strong upward motion over SC, resulting in enhanced precipitation over SC. During La Nin & SIM;a and positive SIOD, the low-level cyclone over the northwest Pacific results from both La Nin & SIM;a and positive SIOD. The positive SIOD enhances La Nin & SIM;a-related cyclonic circulation response through cross-equator Hadley circulation, weakening the water vapor transport towards SC. The positive SIOD-related wave train (PC3-like wave train) plays the dominant role in inducing anomalous anticyclonic circulation and weak descending motion, leading to reduced precipitation over SC.