Development of a Two-Equation Turbulence Model for Mean Shear- and Internal Wave-Driven Mixing

Abstract

Abstract : The long-term goal of the project is to develop realistic, functional parameterizations of stratified turbulent mixing usable in numerical circulation models of oceans and costal seas. Specifically, we aim at developing models which explicitly allow for the coexistence and three-way interaction of three major components of stratified geophysical flows: mean currents, internal inertia gravity waves (IGW) and smallscale, 3D turbulence. Here, mean loosely refers to any current that - in contrast to IGWs and turbulence - can be explicitly resolved in a variety of operational numerical models. Traditional turbulence closures, which our approach extends, only acknowledge the existence of two of the three flow components, turbulence and sheared mean currents. They are thus ignorant of the direct energy flux from breaking IGWs to turbulence. As to its importance, we note that this direct energy flux from IGWs powers the turbulent mixing in the bulk of the depths of the world ocean. The objectives of the project are to (i) develop a two-equation, closure-like turbulence model with turbulent kinetic energy (TKE) production and turbulence length and time scales resulting from mean shear and IGWs simultaneously and (ii) to test the new algorithm through comparisons with observed flows. Our chosen problem is rather challenging. Within the current project we intend to provide a proof of concept.