Atmospheric Rivers Linking Tropical Forcing to Winter Precipitation over Southern China

Abstract Significant winter (December–January–February; DJF) precipitation over southern China (SC) is one of the key features of the East Asian winter monsoon, accounting for nearly 20% of annual precipitation in the area. While oceanic drivers of its interannual variability are extensively studied, the influence of atmospheric rivers (ARs), contributing approximately 30%–40% of the climatological wintertime precipitation in SC, remains unclear. Additionally, how seasonal forecast models capture the impact of tropical sea surface temperature (SST) variations on winter precipitation through ARs requires further investigation using objective metrics. This study identifies a tropical SST pattern involving the El Niño-Southern Oscillation (ENSO), the Indian Ocean Dipole, and the SST anomalies over the western North Pacific (WNP), whose co-evolving structure rapidly develops from the preceding summer to winter. This anomalous SST configuration generates a hemispheric-scale circulation pattern from the tropics to the subtropics, which enhances vertical wind shear and meridional moisture transport over SC, favoring increased AR intrusion into the region. Consequently, significant precipitation anomalies occur particularly near SC along 20°N–30°N, explaining over 50% of the interannual DJF precipitation variability. These ENSO-driven precipitation changes, mediated by AR activity, are reasonably predicted by two operational seasonal forecast systems, suggesting that ENSO and its interaction with WNP SST anomalies serve as the primary sources of forecast skill for winter ARs and SC precipitation. Furthermore, a screening scheme based on the observed SST and circulation states during October and November preceding the target winter is developed to determine the years in which dynamical model forecast skill for SC DJF precipitation is higher than in other winters.