Large eddy simulation of ocean mesoscale eddies

TL;DR

This paper applies 3D LES methods to parameterize mesoscale eddy fluxes in ocean models, implementing a subfilter closure in GFDL MOM6 and evaluating its performance across resolutions, with improvements from a Bardina model at coarser scales.

Contribution

It introduces a novel LES-based subfilter closure for mesoscale eddy fluxes in ocean models, tested within GFDL MOM6, and proposes a Bardina model to enhance coarse-resolution simulations.

Findings

LES convergence at high resolutions

Closure accuracy in mean flow prediction

Bardina model improves coarse-resolution results

Abstract

Mesoscale eddies produce lateral (2D) fluxes that need to be parameterized in eddy-permitting (1/4-degree) global ocean models due to insufficient horizontal resolution. Here, we systematically apply methods from the 3D LES community to parameterize lateral vorticity fluxes produced by mesoscale eddies leveraging an explicit filtering approach together with a dynamic procedure. The developed subfilter closure is implemented into the GFDL MOM6 ocean model and is evaluated in an idealized double-gyre configuration, both a-priori and a-posteriori. For sufficiently resolved grids, the LES simulations converge to the filtered high-resolution data. However, limitations in the proposed closure are observed when the filter scale approaches the energy-containing scales: the a-priori performance drops and a-posteriori experiments fail to converge to the filtered high-resolution data. Nevertheless, the proposed closure is accurate in predicting the mean flow in a-posteriori simulations at all resolutions considered (1/2-1/8 degrees). Finally, we propose parameterizing the thickness fluxes using a Bardina model which further improves simulations at the coarsest resolutions (1/2-1/3 degrees).