Numerical Investigation of Air-Sea Coupling to the Track and Intensity of Landfalling Tropical Cyclones in the South China Sea

Abstract In general, the atmosphere-ocean coupled models can improve the simulation of tropical cyclone (TC) track and intensity, but the mechanism and quantitative analysis of this improvement is still lacking in the existing literature. This study investigates how atmosphere-ocean coupling affects the simulation of eleven tropical cyclones (TCs) in the Northwestern Pacific that made landfalls in China from 2011 to 2020. We use COAWST (Coupled Ocean Atmosphere Wave Sediment Transport), an atmosphere-ocean coupled model with ROMS (Regional Ocean Modeling System) and WRF (Weather Research and Forecast) as its components, and compare it with WRF, a non-coupled atmospheric model. We apply the potential vorticity tendency (PVT) framework to analyze the coupling impact on TC tracks. We find that coupling improves the track simulation by changing the diabatic heating and the residual term in the PVT framework, while the advection terms are less important. Coupling also reduces the sea surface temperature (SST) cooling and the heat flux to the TC, leading to weaker intensity simulation. The coupled model shows significant improvement in both track and intensity errors compared with the non-coupled model. The average SST cooling, heat flux reduction, wind speed reduction, and pressure increase for the coupled model are 0.36 K, 207.52 W·m-2, 3.86 m·s-1, and 6.5 hPa, respectively, for each 1 K SST decrease. These results indicate that the ocean-atmosphere coupling can improve the simulation of typhoon track and intensity, providing some effective theoretical methods for disaster prevention and mitigation in coastal areas.