A Sustained Charging-Triggered Discharging Model for the Severe Convective Outbreak over Western South China in April 2024: The Role of Multi-Scale Interactions

This study investigates the multi-scale dynamical mechanisms of a rare severe convective outbreak (SCO) over western South China from 16–22 April 2024. We propose a “sustained charging–triggered discharging” conceptual model, in which the synergistic interplay between persistent oceanic forcing and synoptic-scale wave dynamics served as the fundamental driver. During the El Niño decay year, record-breaking warm sea surface temperature anomalies in the tropical Indian Ocean and North Atlantic served as the dominant forcing, sustaining an exceptionally strong western Pacific subtropical high (WPSH). The WPSH acted as a “sustained charger”, promoting pre-SCO energy accumulation. Subsequently, the dual Rossby wave trains originating from the North Atlantic functioned as the “discharge switch”, modulating the spatiotemporal phasing of the Ural blocking high (UBH) and the southern branch trough (SBT). This “dual-core” dynamic structure of UBH and SBT drove extreme low-level frontogenesis anomalies, which acted as the direct dynamic trigger for convection, and then released the accumulated unstable energy. This study reveals a distinct pathway for sustained convective activity from the perspective of multi-scale remotely forced dynamics.