Scale-awareness in an energetically constrained eddy parameterisation

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• Julian Mak (HKUST)
• Thursday 09 November 2023, 14:00-15:00
• BAS Seminar Room 330b; https://ukri.zoom.us/j/93867373517.

If you have a question about this talk, please contact Dr Michael Haigh.

There is an increasing interest in mesoscale eddy parameterisations that are scale-aware, normally interpreted to mean that a parameterisation does not require parameter recalibration as the model resolution changes. Here we examine whether Gent-McWilliams (GM) based version of GEOMETRIC , a mesoscale eddy parameterisation that is constrained by a parameterised eddy energy budget, is scale-aware in its energetics. It is generally known that GM-based schemes severely damp out explicit eddies, so the parameterised component would be expected to dominate across resolutions, and we might expect a negative answer to the question of energetic scale-awareness. A consideration of why GM- based schemes damp out explicit eddies leads a suggestion for what we term a splitting procedure: a definition of a “large-scale” field is sought, and the eddy-induced velocity from the GM-scheme is computed from and acts only on the large-scale field, allowing explicit and parameterised components to co-exist. The procedure is primarily investigated within the context of an idealised re-entrant channel model of the Southern Ocean. Evidence is provided that the GM-based version of GEOMETRIC is scale-aware in the energetics as long as we employ a splitting procedure. The splitting procedure also leads to an improved representation of mean states without detrimental effects on the explicit eddy motions at eddy permitting resolutions. If time, results from a joint evaluation of the physical and biogeochemical response in an idealised mid-latitude gyre model at eddy permitting resolution will be presented.

This talk is part of the British Antarctic Survey - Polar Oceans seminar series series.

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