Observations and modeling of typhoon waves in the South China Sea

Abstract

uoy-based observations of surface waves during three typhoons in the South China Sea were used to obtain the wave characteristics. With the local wind speeds kept below 35 m/s, the surface waves over an area with a radius five times that of the area in which the maximum sustained wind was found were mainly dominated by wind-wave components, and the wave-energy distribution was consistent with fetch-limited waves. Swells dominated the surface waves at the front of and outside the central typhoon region. Next, the dynamics of the typhoon waves were studied numerically using a state-of-the-art third-generation wave model. Wind forcing errors made a negligible contribution to the surface wave results obtained using hindcasting. Near-realistic wind fields were constructed by correcting the idealized wind vortex using in situ observational data. If the different sets of source terms were further considered for the forcing stage of the typhoon, which was defined as half inertial period before and after the typhoon arrival time, the best model performance had mean relative biases and root-mean-square-errors of ?0.7% and 0.76 m, respectively, for the significant wave height, and ?3.4% and 1.115 s, respectively, for the peak wave period. Different sets of source terms for wind inputs and white-capping breaking dissipation were also used and the results compared. Finally, twin numerical experiments were performed to investigate the importance of nonlinear wave?wave interactions on the spectrum formed. There was evidence that nonlinear wave?wave interactions efficiently transfer wave energy from high frequencies to low frequencies and prevent double-peak structures occurring in the frequency-based spectrum.