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

Despite advances in understanding severe convective weather in South China, large-scale dynamical pathways that sustain organized mesoscale convection over multiple days remain poorly understood. This study investigates the multi-scale dynamical mechanisms for a rare severe convective outbreak (SCO) over western South China during 16–22 April 2024. We propose a “sustained charging-triggered discharging” conceptual model, in which the synergis-tic interplay between persistent oceanic forcing and synoptic-scale wave dynamics serves 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 were identified as dominant forcing for 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 that originated 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 directly triggered the convection and released/discharged the accumulated unstable energy in the SCO area. This study reveals a distinct pathway for sustained convective activity from the perspective of multi-scale remotely forced dynamics.