Wind-wave-current interaction in hurricanes

High winds, large surface gravity waves, and strong ocean currents simultaneously exist under hurricane conditions. The surface wave field is quite complex and fast varying in space and time and may significantly affect the air-sea fluxes. Moreover, the fluxes into currents may significantly differ from the air input. At the same time, the enhanced current shear may cause refraction in the surface gravity wave field, and the strong current may also affect the air-sea momentum flux by modifying the magnitude of the wind speed relative to the sea surface. The air-sea momentum flux is usually represented by the drag coefficient, Cd, or the sea surface roughness, zo. Field observations have shown large scattering in Cd especially under high wind condition. People argue this large scattering is caused by the spatial and time variation in the wave field. In this study we investigate the effect of different Cd (or zo) parameterization on hurricane track and intensity forecasts through a set of idealized experiments. A fully coupled hurricane-ocean-wave prediction system using the GFDL Hurricane Model, the Princeton Ocean Model and the WaveWatch III wave model is used for this study. The sea surface roughness, zo, is parameterized as a function of wave age and wind speed in this coupled system. Idealized experiments with different translation speeds and initial vortex intensities are conducted to test the effect of different zo parameterization (magnitude and spatial distribution) on hurricane track and intensity forecasts.