Spectral form and source term balance of short gravity wind waves

Abstract

We investigated the spectral structure and source term balance of short gravity waves, based on in situ observations of wave number spectra retrieved by air-sea interaction spar (ASIS) buoys. The behaviors of wave number spectra up to 10 rad/m (the gravity wave regime) were analyzed for a wide range of wind and wave conditions. The observed wave number spectra showed the spectral power laws described by Toba (1973) and Phillips (1958) in addition to the characteristic nodal point at ∼10 rad/m where spectral energy becomes constant over the entire wind speed range. We also improved the third-generation wave model using the nonlinear dissipation term. The wave model reproduced the spectral form in the higher wave number domain. In the equilibrium range, nonlinear transfer played a major role in maintaining equilibrium conditions. On the other hand, in the saturation range, which starts at the upper limit of the equilibrium range, the nonlinear transfer tended to be out of balance with other source terms, and the dissipation term was in balance with wind input.