Effect of model resolution on simulation of tropical cyclone landfall in East Asia based on a comparison of 25- and 50-km HiRAMs: Role of monsoon flow–topography interaction

Abstract The effect of model resolution on the simulation of tropical cyclone (TC) landfall frequency in East Asia (including the South China Sea [SCS], Taiwan and coastal areas of East China [TWCN] and Japan [JP]) was investigated by comparing Atmospheric-Model-Intercomparison-Project-type simulations on the basis of 50-km High Resolution Atmospheric Models (HiRAMs) and 25-km HiRAM. The number of TC landfalls in the TWCN region was realistically simulated by the 50-km HiRAM ensemble model. However, fewer (more) TCs were steered westward (northward) toward the SCS (JP) because of an overestimation of the monsoon trough in the western North Pacific (WNP). The overestimation created a low-level cyclonic circulation anomaly in the WNP, which substantially modified steering flow. Consequently, more (less) TC made landfall in JP (SCS). The overestimation of the monsoon trough was due to an underestimation of the monsoon flow–topography interaction in the Indochina Peninsula Mountains; specifically, the underestimation produced an anomalous east–west overturning circulation in the Indochina Peninsula–WNP, which caused the ascending branch in the WNP to favor convection and strengthened the monsoon trough. The underestimation of the monsoon flow–topography interaction in the Indochina Peninsula Mountains was improved substantially by increasing the model’s horizontal resolution with the 25-km HiRAM. The improvement in the monsoon flow–topography interaction further reduced the overestimation of the WNP monsoon trough, number of TC geneses, and track frequency.