Influence of Distinct Intraseasonal Oscillation Intensities on Regional Persistent Extreme Precipitation Events over South China

This study investigated the characteristics and mechanisms of summer regional persistent extreme precipitation events (RPEPEs) over South China (SC) modulated by distinct intensity regimes of 10–30-day intraseasonal oscillation (ISO). Diagnostic analyses revealed that the spatiotemporal evolution of RPEPEs exhibits robust phase-locking with the 10–30-day intraseasonal precipitation. By classifying RPEPEs into strong-ISO (SRPEPE) and weak-ISO (WRPEPE) composites based on the amplitude of 10–30-day filtered precipitation, we demonstrate a 14.6% enhancement in peak precipitation intensity during SRPEPEs compared to WRPEPEs. These distinct precipitation regimes are governed by fundamentally different Rossby wave teleconnection patterns over Eurasia. During SRPEPEs, a robust southeastward-propagating 10–30-day Rossby wave train originating from the Barents Sea traverses midlatitude Eurasia, effectively perturbing the northwestern Pacific upper-level circulation and establishing a favorable dynamic environment over SC. In contrast, WRPEPEs are associated with weaker eastward-propagating wave trains constrained along the subtropical jet stream. The horizontal convergence of background moisture driven by 10–30-day winds significantly amplifies lower-tropospheric humidity during SRPEPEs. The thermal advection of background temperature by 10–30-day geostrophic winds enhances baroclinic instability and vertical motion, intensifying precipitation under these moisture conditions.