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Eddy-induced transport in layered models
Mats Bentsen
Uni Research Climate, Norway
(Abstract received 04/30/2015 for session X)
ABSTRACT
In large scale ocean models the parameterization of mesoscale eddies is often realized by tracer diffusion along neutral surfaces in combination with an eddy-induced transport that adiabatically tend to reduce available potential energy. The latter is usually achieved with some variant of the Gent-McWilliams (GM) parameterization. In layered models with isopycnic vertical coordinate, eddy-induced transport is commonly parameterized by layer interface diffusion and this approach is similar to the GM parameterization with some exceptions: GM is trying the flatten neutral surfaces, not isopycnal surfaces; with a Laplacian operator, the interface diffusion is moving the model state towards a state with interfaces of constant depth (Boussinesq model) or constant pressure (non-Boussinesq model), neither of which is necessarily a state of no remaining available potential energy; near the surface, interface diffusion is profoundly different from GM when a non-isopycnic bulk surface mixed layer or other non-isopycnic interfaces (e.g. hybrid vertical coordinate) are present. The eddy-induced transport parameterization in the version of MICOM used as the ocean component of the Norwegian Earth System Model has recently been modified to follow the GM approach more closely, addressing the above-mentioned deviations by the previously used interface diffusion. The modified parameterization will be presented along with preliminary results.
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2015 LOM Workshop, Copenhagen, Denmark June 2nd - 4th, 2015