Southern China Winter Rainfall Modulated by South China Sea warming

New insight into the contribution of anomalous South China Sea (SCS) warming is proposed to understand strong southern China (SC) winter rainfall. El Nino events, which weaken the East Asian winter monsoon (EAWM), favor SC winter rainfall. However, the changes in SC winter rainfall are not always in phase with the El Nino-Southern Oscillation, making the prediction of East Asian climate challenging. Here, we show that the increased moisture associated with the warming SCS induced by the weakening western boundary current leads to increased meridional moisture transport to SC. Particularly, during the El Nino mature winter phase, this effect works jointly with a weakened EAWM to determine an increased rainfall over SC. Therefore, we suggest that the thermal state of the SCS should be considered when large-scale tropical ocean-atmosphere variability is utilized to predict SC winter rainfall. Plain Language Summary Climate extremes, such as strong southern China (SC) winter rainfall, greatly affect socioeconomic activities and raise great concerns. The South China Sea (SCS) acts as a "portal" to SC and significantly modulates the nonlinear moisture transport to SC. When the SCS is warm enough, the "portal" opens and allows abundant moisture transport toward SC. Particularly during the El Nino mature winter, this effect works jointly with a weakened East Asian winter monsoon to determine increased winter rainfall over SC.