Local-scale circulation associated with enhanced poleward moisture transport for Meiyu-Baiu heavy rainfall over western Japan

Abstract

Abstract Heavy rainfall events in western Japan during early July have become more frequent, yet the underlying mechanism behind this trend during the late stage of the Meiyu-Baiu rainy season remains unclear. Our long-term analysis of short-duration events revealed that a quasi-stationary Rossby wave train enhances the poleward transport of moisture from the western Pacific, contributing to the frequent occurrence of heavy rainfall events over western Japan. The local-scale circulation over the East China Sea plays a substantial role in producing this quasi-stationary Rossby wave train, which is closely linked to enhanced deep convection over the Kuroshio warm current, characterized by a distinct sea surface temperature (SST) front. The coarse resolution of both the model and SST data may hinder the ability of climate simulations to capture the local-scale circulation, underscoring the importance of quasi-stationary atmospheric circulation for a better understanding of heavy rainfall events through poleward moisture transport.