Effect of model resolution on simulation of tropical cyclone landfall in East Asia based on a comparison of 25- and 50-km HiRAMs

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 (AMIP) 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 in model was primarily resulted from compounding factors, including the AMIP type simulation, upscale feedback of TCs to mean flow and the monsoon flow–topography interaction in the Indochina Peninsula Mountains and Philippine. First, the SST was negatively correlated with precipitation in the WNP during the typhoon season for the observation. Conversely, the SST–precipitation relationship was positive in the AMIP run. Second, the upscale feedback of TCs to mean flow (monsoon trough) was overestimated, which in term contributed to the overestimation of monsoon trough. Third, the model underestimated the mountain lifting effect in the Indochina Peninsula and Philippine. Overall, the aforementioned biases were substantially improved by increasing model’s horizontal resolution from 50-km to 25-km HiRAM.