Parameterized Mixing in Mesoscale-resolving Global Ocean Models: A Large Eddy Simulation Approach

Inaccurate parameterization of sub-grid eddies can cause excessive damping and spurious diapycnal mixing in high-resolution [O(10km)] ocean models. The Mesoscale Ocean Large Eddy Simulation (MOLES) approach provides a framework for developing resolution- and flow-adaptive parameterizations of eddy effects. Large eddy simulation techniques are commonly used to simulate 3D turbulence, and MOLES is modified to be appropriate for the more two-dimensional nature of mesoscale ocean turbulence.

Here we investigate the effect of MOLES in high-resolution ocean models. We will contrast results, and cost, from a suite of high-resolution idealized (MITgcm) and global (0.1^o POP2) ocean models, which use a variety of eddy mixing parameterizations. These include MOLES based upon 2D turbulence theory, MOLES based upon quasi-geostrophic (QG) turbulence theory, and traditional biharmonic schemes.

We compare the effect of different parameterizations on the dynamics of simulated ocean flow. In an idealized model, using MOLES improves the spectra of kinetic energy and potential enstrophy. In a global model, using MOLES results in greater energy and variability near the grid scale, decreases the ACC mass transport, and affects the global sinks of kinetic energy.