Parameterisation of meso-scale mixing in the ocean

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Ocean models which do not resolve the energetic meso-scale eddy field have to parameterise its effects on the large-scale circulation. This effect is for instance important in western boundary currents, where meso-scale eddies balances the planetary vorticity change, and in the Southern Ocean where they control both the zonal ow and the meridional overturning circulation. Further, meso-scale eddies are important for the ventilation of the interior ocean with dissolved gases. In current ocean climate models, a constant lateral diffusivity K appropriate to the Gent and McWilliams (1990) parameterisation is used. However, a constant diffusivity K is inadequate for climate change simulations and decadal climate predictions, since K does vary both in time and in space. We propose to advance the current meso-scale eddy parameterisation in ocean climate models by applying and improving a mixing length approach for K, based on an eddy kinetic energy (EKE) budget, an eddy length scale and a vertical structure function. The parameters in the EKE budget and the structure function will be estimated using a global ocean model and its adjoint constraining the model and the closure to observational estimates.