DIRECT SIMULATION OF INTERNAL WAVE ENERGY-TRANSFER

A three-dimensional nonhydrostatic numerical model is used to calculat e nonlinear energy transfers within decaying Garrett-Munk internal wav efields. Inviscid wave interactions are calculated over horizontal sca les from about 1 to 80 km and for vertical mode numbers less than abou t 40 in an exponentially stratified model ocean 2000 m deep. The rate of energy transfer from these scales to smaller, numerically damped sc ales is used to make predictions of the dissipation rate epsilon in th e open ocean midlatitude thermocline. In agreement with the theoretica l analyses based on resonant interaction and eikonal theories, the sim ulation results predict epsilon proportional to <(E)over tilde (2)> N- 2, where (E) over tilde and N are the internal wave energy density and the ambient buoyancy frequency respectively. The magnitudes of the si mulated dissipation rates are shown to be in good agreement with the d issipation measurements taken from six diverse sites in the midlatitud e thermocline. The results suggest that the rates of dissipation and m ixing in the ocean thermocline are controlled by the nonlinear dynamic s of the large-scale energy-containing internal waves.