Experimental description of turbulent energy fluxes associated with the parametric subharmonic instability
Yvan Dossmann, Philippe Odier, Christophe Brouzet, Sylvain Joubaud, Baptiste Bourget and Thierry Dauxois, Ecole Normale Supérieure de Lyon, Laboratoire de Physique, Lyon, France
Abstract:
In the ocean, the parametric subharmonic instability (PSI) is a potential energy pathway to irreversible mixing that is not fully understood. It consists in the destabilization of a primary internal wave generation leading to the radiation of two secondary waves of lower frequencies and different wave vectors. In the process, internal wave energy is carried down to smaller scales. We investigate mixing induced by the process of PSI relying on turbulent fluxes measurements in laboratory experiments. Simultaneous two-dimensional velocity and density measurements at high resolution are performed using combined PIV/LIF techniques. The turbulent diffusivity is directly assessed from turbulent fluxes calculations. It reaches values up Kt=2.10⁻⁵ m²/s in the configuration of unstable PSI. It is comparable to the pelagic value for turbulent diffusivity in the ocean. These results could help to refine parameterizations of the role played by the PSI mechanism in diapycnal mixing in oceanic numerical simulations.
Development of the parametric subharmonic instabilty for a mode-1 internal wave.
