Spatial diversity of multiple tropical cyclone events over the western North Pacific and associated physical processes

Abstract Multiple tropical cyclone (TC) events (MTCEs) can cause disproportionate damages beyond the cumulative impacts of individual TCs, yet their physical processes and driving mechanisms remain poorly understood. This study focuses on spatial diversity in MTCE occurrence and their associated physical processes over the western North Pacific (WNP). Based on spatial features, MTCEs are objectively classified into three clusters: eastern induced (EI) cluster, western induced in the nearshore (WI-N) cluster, and western induced in the open sea (WI-O) cluster. The EI cluster is driven by the strengthened South China Sea summer monsoon, with TCs forming within the monsoon trough and confluence regions. The WI-N cluster primarily arises from the interaction between the monsoon westerlies and easterlies associated with an anomalous anticyclone. The WI-N cluster is characterized by tropical wave trains, potentially linked to TC-induced Rossby wave dispersion and easterly waves. Dynamic genesis potential analysis reveals that enhanced midlevel vertical motion dominates the dynamic factors controlling the MTCE formation across the WNP. Meanwhile, barotropic energy conversions, arising from the convergence and meridional shear of large-scale zonal winds, serve as the primary sources of eddy kinetic energy for MTCE formation. Upper-level baroclinic energy conversions also play a significant role, especially for the WI-N and WI-O clusters. Time decomposition reveals that factors across multiple time scales, including the quasi-biweekly oscillation, intraseasonal oscillations, and low-frequency variability, contribute to WNP-MTCE formation. Our findings offer a comprehensive view to better understand the spatial diversity of MTCE over the WNP.