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On transport tensor of dynamically unresolved oceanic mesoscale eddies

Published online by Cambridge University Press:  23 March 2022

E.A. Ryzhov Open the ORCID record for E.A. Ryzhov [Opens in a new window]  and
P. Berloff Open the ORCID record for P. Berloff [Opens in a new window]
E.A. Ryzhov
Affiliation:
Department of Mathematics, Imperial College London, Huxley Building, London SW7 2AZ, UK Pacific Oceanological Institute, Baltiyskaya 43, 690041, Vladivostok, Russia
P. Berloff*
Affiliation:
Department of Mathematics, Imperial College London, Huxley Building, London SW7 2AZ, UK Institute of Numerical Mathematics, Russian Academy of Sciences, Gubkina 8, 119333, Moscow, Russia
*
†Email address for correspondence: [email protected]
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Abstract

Parameterizing mesoscale eddies in ocean circulation models remains an open problem due to the ambiguity with separating the eddies from large-scale flow, so that their interplay is consistent with the resolving skill of the employed non-eddy-resolving model. One way to address the issue is by using recently formulated dynamically filtered eddies. These eddies are obtained as the field errors of fitting some given reference ocean circulation into the employed coarse-grid ocean model. The main strengths are (i) no explicit spatio-temporal filter is needed for separating the large-scale and eddy flow components, (ii) the eddies are dynamically translated into the error-correcting forcing that perfectly augments the coarse-grid model towards reproducing the reference circulation. We uncovered physical properties of the eddies by interpreting involved nonlinear eddy/large-scale interactions via the classical flux-gradient relation. We described the eddies in terms of their full, space–time dependent transport tensor, which was made unique by constraining it to be the same for the potential vorticity, momentum and buoyancy fluxes. Both diffusive and advective parts of the transport tensor were found to be significant. The diffusive tensor component is characterised by polar eigenvalues and is further decomposed into isotropic and filamentation components. The latter component completely dominates, therefore, it should be taken into account by eddy parameterizations, which is not yet the case. We also showed that spatial inhomogeneities of the transport tensor components are important. Comparing these properties with those obtained for more common, locally filtered eddies revealed that they are distinctly different.

JFM classification

Geophysical and Geological Flows: Baroclinic flows Geophysical and Geological Flows: Ocean circulation Geophysical and Geological Flows: Quasi-geostrophic flows
Type
JFM Papers
Information
Journal of Fluid Mechanics , Volume 939 , 25 May 2022 , A7
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Copyright
© The Author(s), 2022. Published by Cambridge University Press

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References

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