ON TRIAD INTERACTIONS IN A LINEARLY STRATIFIED OCEAN

Triad interactions in a linearly stratified ocean are studied numerica lly using a Garrett-Munk energy spectrum as the initial condition. It is found by bispectrum analysis that wave-mean flow interactions domin ate and resonant interactions are limited to very large scales. Resona nt triads of parametric subharmonic instability type play an insignifi cant role in the energy distribution. Local sum resonant triads provid e the most effective energy transfer at very large scales. The analysi s of triadic energy transfer rates suggests that triad configuration d etermines the energy flow pattern. When the modes with zero horizontal wavenumber are set to zero, resonant interactions arise. Thus, over m ost of the Garrett-Munk spectrum the energy level is low enough for re sonance, but due to strong nonlinearities induced by horizontal curren ts, resonance is destroyed and wave-mean flow interactions dominate. I f the energy level is reduced by a factor of 100, the number of resona nt modes increases but wave-mean flow interactions remain important at high wavenumber.