Performance of a Saturation-Based Dissipation-Rate Source Term in Modeling the Fetch-Limited Evolution of Wind Waves

Abstract

A new formulation of the spectral dissipation source term S_ds for wind-wave modeling applications is investigated. This new form of S_ds is based on a threshold behavior of deep-water wave-breaking onset associated with nonlinear wave-group modulation. It is expressed in terms of the azimuth-integrated spectral saturation, resulting in a nonlinear dependence of dissipation rates on the local wave spectrum. Validation of the saturation-based S_ds is made against wave field parameters derived from observations of fetch-limited wind-wave evolution. Simulations of fetch-limited growth are made with a numerical model featuring an exact nonlinear form of the wave–wave-interactions source term S_nl. For reference, the performance of this saturation-based S_ds is compared with the performance of the wave-dissipation source-term parameterization prescribed for the Wave Modeling Project (WAM) wind-wave model. Calculations of integral spectral parameters using the saturation-based model for S_ds agree closely with fetch-limited observations. It is also shown that the saturation-based S_ds can be readily adjusted to accommodate several commonly used parameterizations of the wind input source term S_in. Also, this new form of S_ds provides greater flexibility in controlling the shape of the wave spectrum in the short gravity-wave region.