3D LES methods for lateral parameterizations of ocean mesoscale eddies*

Mesoscale eddies in the ocean play a significant role in the mixing of ocean tracers and closing the energy budget. Current climate ocean models operate at eddy-permitting resolution (¼ degree) where the significant part of mesoscale eddy fluxes needs to be parameterized. The mesoscale parameterizations can be improved by applying 3D LES methods to quasi-2D equations of the ocean.

In this work, we develop the subgrid closure of the lateral momentum fluxes based on the 3D LES subgrid closure of Horiuti1997 and implement it in the GFDL MOM6 ocean model in an idealized configuration. The subgrid closure contains two free parameters which are estimated dynamically. We show the convergence of the LES model to the filtered high-resolution simulation at a fixed filter width, demonstrating that the developed subgrid closure is of explicit filtering type. We further show that developed subgrid closure accurately reproduces metrics of the mean flow for a range of resolutions: potential energy and error in the time-mean sea surface height. Finally, we propose an LES analog of Gent-McWilliams parameterization by approximating mass fluxes with the Leonard flux.