Numerical evaluation of the spectral evolution of internal gravity waves due to wave-wave interactions

Abstract

The kinetic energy spectra of oceanic internal gravity waves (IGWs) from recent field measurements and wave turbulence theory exhibit large variability, deviating from the standard Garrett-Munk (GM) model. However, the current finescale parameterization of turbulent dissipation is based on the GM model, which does not consider general spectra. Thus an improved estimate of energy cascade across scales for different spectra is needed for better parameterization of ocean mixing for global circulation and climate models. In this work, we conduct direct calculation of energy transfer based on the kinetic equation, which describes the spectral evolution of IGWs due to wave-triad interactions. First, dominant mechanisms are identified, i.e., local and scale-separated interactions (including parametric subharmonic instability, elastic scattering and induced diffusion). Local interactions provide a forward cascade in frequency that were not understood before. Second, energy flux across a critical vertical wavenumber providing energy available for dissipation is calculated for different spectra. The importance of local interactions for such downscale cascade is emphasized. This will shed light on a new formulation of finescale parameterization incorporating varying spectral forms of IGWs and a realistic ocean environment.