Triadic Instability and Internal Tide Dissipation in Ocean

Several previous numerical suggest the presence of a critical latitude cor- responding to an enhanced energy dissipation associated to mixing. The mechanism proposed to explain this enhanced energy transfer from inter- nal tides to dissipation is the formation of a triadic instability. This triadic instability corresponds to a primary internal tide at frequency ω0 which gen- erates spontaneously two secondary waves at frequencies ω0 − f and f , where f is the Coriolis frequency. At the critical latitude, the frequencies of the secondary waves are the same and equal to ω0/2 which is equal to f; this particular case corresponds to the parametric subharmonic instability.

We propose to study the existence of triadic instabilities in the ocean which means we are taking into account the Earth rotation in the equations via the Coriolis frequency f. The purpose of the project is to study the existence of triadic interactions in a rotating frame in the case of a semi realistic ocean (numerical simulations). The first results seem to show that the observed dissipation in the 2D numerical simulations can not be linked to the mechanism of a triadic instability. We complete these results with 3D numerical simulations.