Possible Mechanisms for the Record‐Breaking Persistent Extreme Rainfall Event Over Southern China in April 2024: Synergistic Effects of Multiscale Systems

Abstract In April 2024, southern China suffered a record‐breaking persistent extreme rainfall event (PERE), affecting 1.60 million people and causing direct economic losses of 11.98 billion RMB. This study reveals the synergistic effects of sea surface temperature (SST) and intraseasonal atmospheric circulation. Positive SST anomalies in tropical Indian Ocean (TIO) strengthen the western Pacific subtropical high (WPSH) via Gill‐type response (basical theory describing the atmospheric response to external forces such as tropical SST), enhancing moisture transport to southern China. The 10–30‐day intraseasonal oscillation (ISO) along the subtropical westerly jet initiates the event by inducing a low‐pressure and ascending motion over southern China. The 30–90‐day ISO along the polar front jet sustains the event by intensifying East Asian westerly jet and maintaining ascending motion over southern China. Furthermore, North Atlantic SST anomalies enhance North Atlantic jet stream, promoting downstream propagation of intraseasonal wave trains via energy conversion.