Implementation of a geometrically and energetically constrained mesoscale eddy parameterization in an ocean circulation model

TL;DR

This paper introduces GEOMETRIC, a new mesoscale eddy parameterization framework that constrains eddy fluxes using an eddy energy budget, improving ocean circulation model accuracy at coarse resolutions.

Contribution

The paper presents a novel eddy parameterization framework that incorporates energetic constraints, shifting focus from flux closure to eddy energetics representation.

Findings

GEOMETRIC reproduces key model sensitivities like circumpolar transport and overturning circulation.

Eddy saturation emerges in the coarse resolution model using GEOMETRIC.

Differences are noted due to the simple eddy energy budget, indicating areas for future improvement.

Abstract

The global stratification and circulation of the ocean and their sensitivities to changes in forcing depend crucially on the representation of the mesoscale eddy field. Here, a geometrically informed and energetically constrained parameterization framework for mesoscale eddies --- termed GEOMETRIC --- is proposed and implemented in three-dimensional primitive equation channel and sector models. The GEOMETRIC framework closes mesoscale eddy fluxes according to the standard Gent--McWilliams scheme, but with the eddy transfer coefficient constrained by the depth-integrated eddy energy field, provided through a prognostic eddy energy budget evolving with the mean state. It is found that coarse resolution calculations employing GEOMETRIC broadly reproduce model sensitivities of the eddy permitting reference calculations in the emergent circumpolar transport, meridional overturning circulation profile and the depth-integrated eddy energy signature; in particular, eddy saturation emerges in the sector configuration. Some differences arise, attributed here to the simple prognostic eddy energy budget employed, to be improved upon in future investigations. The GEOMETRIC framework thus proposes a shift in paradigm, from a focus on how to close for eddy fluxes, to focusing on the representation of eddy energetics.