Mixing in the ocean, from currents to waves…
Orateurs : R. Ecke and P. Odier
Los Alamos National Laboratory, Los Alamos, USA, Laboratoire de Physique de l’ENS de Lyon
Abstract : The ocean is a stably stratified medium, where the heavy fluid lies at the bottom with the lighter fluid on top. Mixing often occurs, however, that changes the stratification : in some places like the Denmark Strait or the Mediterranean outflow, heavier currents, as they flow down, entrain ambient fluid that results in density change of the current. In other places, where internal gravity waves can become unstable and overturn, a conversion of turbulent kinetic energy to potential energy can occur, contributing to the "return flow" of the thermohaline circulation. We will discuss experiments that improve our understanding of some of the mechanisms involved in these phenomena. We begin by presenting results on hydrodynamic instability and mixing of gravity currents owing to Kelvin-Helmholtz and Holmboe instabilities where simultaneously measured velocity and density in a perpendicular plane allow a very complete quantitative characterization of the flow. Using similar experimental techniques, we then discuss internal gravity waves which are inherently unstable through a triadic resonant interaction (TRI). We present several aspects of this interaction and show how it is closely linked to slow evolution of the density profile of the fluid.
Date et lieu : le Vendredi 30 Septembre 2016 à 11h00, salle de séminaire IRPHE