The Variable Impact of Aerosol Reduction on Tropical Cyclone Precipitation

Prior research has established that higher aerosol concentrations can influence both precipitation formation and tropical cyclone intensity. As climate mitigation efforts advance, however, anthropogenic aerosol levels are projected to decline. This study investigates how such a decrease in aerosol concentration may alter tropical cyclone precipitation patterns, using Typhoons Haikui and Koinu as case studies. Simulations were conducted with the Weather Research and Forecasting (WRF) model employing the Thompson aerosol-aware microphysics scheme, in which water-friendly aerosol concentrations were reduced by two orders of magnitude. Results show that lower aerosol concentrations consistently expand the area of precipitation in both cyclones by enhancing the warm-rain process. Nevertheless, total precipitation amounts respond differently: they increase for Haikui but decrease for Koinu. This divergence is attributed to the relative dominance of warm-rain versus ice-phase microphysical processes and associated changes in upper-level convection.