Future changes in tropical cyclone intensity and frequency over the Western North Pacific based on 20-km HiRAM and MRI models

The future changes in tropical cyclone (TC) intensity and frequency over the western North Pacific (WNP) under global warming remain uncertain. In this study, we investigated such changes using 20-km resolution HiRAM and Meteorological Research Institute (MRI) models, which can realistically simulate the TC activity in the present climate. We found that the mean intensity of TCs in the future (2075-99) would increase by approximately 15%, along with an eastward shift of TC genesis location in response to the El Niño-like warming. However, the lifetime of future TCs would be shortened because the TCs tend to have more poleward genesis locations and move faster due to a stronger steering flow related to the strengthened WNP subtropical high in a warmer climate. In other words, the enhancement of TC intensity in the future is not attributable to the duration of TC lifetime. To understand the processes responsible for the change in TC intensity in a warmer climate, we applied the budget equation of synoptic-scale eddy kinetic energy along the TC tracks in model simulations. The diagnostic results suggested that both the upper-level baroclinic energy conversion (CE) and lower-level barotropic energy conversion (CK) contribute to the intensified TCs under global warming. The increased CE results from the enhancement of TC-related perturbations of temperature and vertical velocity over the subtropical WNP, whereas the increased CK mainly comes from synoptic-scale eddies interacting with enhanced zonal-wind convergence associated with seasonal-mean and intraseasonal flows over Southeast China and the northwestern sector of WNP.