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 Sds for wind-wave modeling applications is investigated. This new form of Sds 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 Sds 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 Snl. For reference, the performance of this saturation-based Sds 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 Sds agree closely with fetch-limited observations. It is also shown that the saturation-based Sds can be readily adjusted to accommodate several commonly used parameterizations of the wind input source term Sin. Also, this new form of Sds provides greater flexibility in controlling the shape of the wave spectrum in the short gravity-wave region.