Deterministic model of the eddy dynamics for a midlatitude ocean model

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Authors

Takaya Uchida, Bruno Deremble , Stephane Popinet 

Abstract

Mesoscale eddies, the weather system of the oceans, although being on the scales of O(20-100 km), have a disproportionate role in shaping the mean jets such as the separated Gulf Stream in the North Atlantic Ocean, which is on the scale of O(1000 km) in the along-jet direction. With the increase in computational power, we are now able to partially resolve the eddies in basin-scale and global ocean simulations, a model resolution often referred to as mesoscale permitting. It is well known, however, that due to grid-scale numerical viscosity, mesoscale-permitting simulations have less energetic eddies and consequently weaker eddy feedback onto the mean flow. In this study, we run a quasi-geostrophic model at mesoscale-resolving resolution in a double gyre configuration and formulate a deterministic closure for the eddy rectification term of potential vorticity (PV), namely, the eddy PV flux divergence. We successfully reproduce the spatial patterns and magnitude of eddy kinetic and potential energy diagnosed from the model. One novel point about our approach is that we account for non-local eddy feedbacks onto the mean flow by solving the `sub-grid' eddy PV equation prognostically in addition to the mean PV. In return, we are able to parametrize the variability in total (mean+eddy) PV at each time step instead of solely the mean PV. A closure for the total PV is beneficial as we are able to account for both the mean state and extreme events.

DOI

https://doi.org/10.31223/X5WP71

Subjects

Physical Sciences and Mathematics

Keywords

Quasi-geostrophy, Mesoscale eddy closure

Dates

Published: 2021-09-29 03:54

Last Updated: 2021-09-29 07:54

License

CC BY Attribution 4.0 International

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