Examination of wind-wave interaction source term in WAVEWATCH III with tropical cyclone wind forcing

Results of drag coefficient (C_D) from field observations and laboratory wave tank experiments indicate that the operational wave model can overestimate wind energy input under high wind conditions. The wind-wave interaction source term in WAVEWATCH III has been modified to examine its behavior with tropical cyclone wind forcing. Using high resolution wind input, numerical experiments under idealized wind field and tropical cyclone Bonnie (1998) were designed to evaluate performance of the modified models. Both experiments indicate that the modified models with reduced C_D significantly decrease wind energy input into the wave model and then simulate lower significant wave height (SWH) than the original model. However, the effects on spatial distribution of SWH, mean wavelength, mean wave direction, and directional wave spectra are insignificant. Due to the reduced wind energy input, the idealized experiment shows that the modified models simulate lower SWH than the original model in all four quadrants. The decrease in the front quadrants is significantly larger than that in the rear quadrants; it is larger under higher winds than lower winds. The realistic experiment on tropical cyclone Bonnie shows that the modified model with the various downward trends of C_D in high winds creates a simulation that agrees best with scanning radar altimeter observations.