Comparing Two Parameterizations for the Restratification Effect of Mesoscale Eddies in an Isopycnal Ocean Model

Author:

Loose Nora12ORCID,Marques Gustavo M.3ORCID,Adcroft Alistair2ORCID,Bachman Scott3ORCID,Griffies Stephen M.24ORCID,Grooms Ian1ORCID,Hallberg Robert W.24,Jansen Malte F.5ORCID

Affiliation:

1. Department of Applied Mathematics University of Colorado Boulder CO USA

2. Atmospheric and Oceanic Sciences Princeton University Princeton NJ USA

3. Climate and Global Dynamics Laboratory National Center for Atmospheric Research Boulder CO USA

4. NOAA Geophysical Fluid Dynamics Laboratory Princeton NJ USA

5. Department of the Geophysical Sciences The University of Chicago Chicago IL USA

Abstract

AbstractThere are two distinct parameterizations for the restratification effect of mesoscale eddies: the Greatbatch and Lamb (1990, GL90, https://journals.ametsoc.org/view/journals/phoc/20/10/1520-0485_1990_020_1634_opvmom_2_0_co_2.xml?tab_body=abstract-display) parameterization, which mixes horizontal momentum in the vertical, and the Gent and McWilliams (1990, GM90, https://journals.ametsoc.org/view/journals/phoc/20/1/1520-0485_1990_020_0150_imiocm_2_0_co_2.xml) parameterization, which flattens isopycnals adiabatically. Even though these two parameterizations are effectively equivalent under the assumption of quasi‐geostrophy, GL90 has been used much less than GM90, and exclusively in z‐coordinate models. In this paper, we compare the GL90 and GM90 parameterizations in an idealized isopycnal coordinate model, both from a theoretical and practical perspective. From a theoretical perspective, GL90 is more attractive than GM90 for isopycnal coordinate models because GL90 provides an interpretation that is fully consistent with thickness‐weighted isopycnal averaging, while GM90 cannot be entirely reconciled with any fully isopycnal averaging framework. From a practical perspective, the GL90 and GM90 parameterizations lead to extremely similar energy levels, flow and vertical structure, even though their energetic pathways are very different. The striking resemblance between the GL90 and GM90 simulations persists from non‐eddying through eddy‐permitting resolution. We conclude that GL90 is a promising alternative to GM90 for isopycnal coordinate models, where it is more consistent with theory, computationally more efficient, easier to implement, and numerically more stable. Assessing the applicability of GL90 in realistic global ocean simulations with hybrid coordinate schemes should be a priority for future work.

Funder

National Science Foundation

National Oceanic and Atmospheric Administration

Publisher

American Geophysical Union (AGU)

Subject

General Earth and Planetary Sciences,Environmental Chemistry,Global and Planetary Change

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