1. Comparing Two Parameterizations for the Restratification Effect of Mesoscale Eddies in an Isopycnal Ocean Model.
- Author
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Loose, Nora, Marques, Gustavo M., Adcroft, Alistair, Bachman, Scott, Griffies, Stephen M., Grooms, Ian, Hallberg, Robert W., and Jansen, Malte F.
- Subjects
MESOSCALE eddies ,PARAMETERIZATION ,GRID cells ,OCEAN ,LARGE eddy simulation models ,EDDIES ,RESEARCH questions ,OCEAN circulation - Abstract
There 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%5f1990%5f020%5f1634%5fopvmom%5f2%5f0%5fco%5f2.xml?tab%5fbody=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%5f1990%5f020%5f0150%5fimiocm%5f2%5f0%5fco%5f2.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. Plain Language Summary: Ocean models are complex simulations run on large supercomputers, and are useful for predicting changes in ocean circulation and climate. Ocean models divide the globe into grid cells. Choosing many, very small grid cells is not feasible because the simulations would take too much time and would be too expensive. Therefore, the grid cells in most ocean models are not small enough to simulate mesoscale eddies. Mesoscale eddies are swirling motions that are less than 100 km wide and play an important role in transporting heat and carbon throughout the ocean. To still account for the effects of mesoscale eddies, one can use approximate "parameterizations." Which parameterization is "best" is an ongoing research question. This paper compares two parameterizations that simulate the effect of mesoscale eddies in two distinct ways: the commonly used Gent and McWilliams (1990, https://journals.ametsoc.org/view/journals/phoc/20/1/1520-0485%5f1990%5f020%5f0150%5fimiocm%5f2%5f0%5fco%5f2.xml) parameterization and the less commonly used Greatbatch and Lamb (1990, https://journals.ametsoc.org/view/journals/phoc/20/10/1520-0485%5f1990%5f020%5f1634%5fopvmom%5f2%5f0%5fco%5f2.xml?tab%5fbody=abstract-display) parameterization. This paper shows that the two parameterizations impact ocean circulation in a very similar way, and that for a certain class of models the Greatbatch and Lamb (1990, https://journals.ametsoc.org/view/journals/phoc/20/10/1520-0485%5f1990%5f020%5f1634%5fopvmom%5f2%5f0%5fco%5f2.xml?tab%5fbody=abstract-display) parameterization has advantages because it is more consistent with physical and mathematical theory, is easier to code, and leads to faster computations. Key Points: We compare the Greatbatch and Lamb (1990, GL90, https://journals.ametsoc.org/view/journals/phoc/20/10/1520-0485%5f1990%5f020%5f1634%5fopvmom%5f2%5f0%5fco%5f2.xml?tab%5fbody=abstract-display) and the Gent and McWilliams (1990, GM90, https://journals.ametsoc.org/view/journals/phoc/20/1/1520-0485%5f1990%5f020%5f0150%5fimiocm%5f2%5f0%5fco%5f2.xml) parameterizations in an isopycnal ocean modelGL90 leads to very similar flow as GM90, for non‐eddying through eddy‐permitting resolutionWe argue, however, that for isopycnal coordinate models GL90 is more consistent with theory than GM90 [ABSTRACT FROM AUTHOR]
- Published
- 2023
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