Investigating the impacts of wave state and sea spray on typhoon via a coupled atmosphere-wave system: the idealized case

Based on the proposed parameterizations of air-sea momentum and heat fluxes including the effects of wave state and sea spray, the atmospheric Weather Research and Forecast (WRF) model is coupled with the third generation wave model WAVEWATCH III to establish a coupled atmosphere-wave system. In order to investigate the impacts of sea-state-dependent roughness, dissipative heating and sea spray heat flux on typhoon system, several experiments are designed to simulate an idealized typhoon using the coupled model. It is shown that sea-state-dependent roughness increases sea surface friction, reduces typhoon intensity and surface wave height. When using the wave-state and sea-spray related aerodynamic roughness parameterization instead of the Charnock relation, the minimum central pressure of the typhoon in the coupled simulation increased by about 5%, and the maximum significant wave height decreased by about 6%. It is also found that the inclusion of dissipative heating increases the air-sea heat flux, thus intensifies the typhoon system, leading to an 8-10% increase of minimum central pressure, a 6-10% increase of maximum wind speed at 10-m height and a 10-15% increase of maximum significant wave height. Incorporating sea spray heat flux also substantially strengthens the typhoon system, and increases surface wind speed and wave height. In addition, the impacts of sea-state-dependent sea surface roughness, dissipative heating and sea spray heat flux on the typhoon system are related to each other through marine boundary layer processes. With all three effects included, the minimum central pressure of the typhoon system in the coupled simulation is 10.7 hPa deeper than that in the uncoupled simulation, corresponding to a 14% increase of the intensity of typhoon system. The simulated maximum wind speed and significant wave height increased by 18% and 4%, respectively. Meanwhile the total air-sea heat flux in the coupled simulation increased by about 10%, with the latent heat flux increasing more significantly by about 18%.