Parameterising meso-scale eddy momentum fluxes based on potential vorticity mixing and a gauge term

Meso-scale fluctuations are known to drive large-scale zonal flows in the ocean, a mechanism which is currently missing in non-eddy-resolving ocean models. A closure for meso-scale eddy momentum fluxes is evaluated in a suite of idealised eddying channel models, featuring eddy-driven zonal jets. It is shown how the appearance of zonal jets, which act as mixing barriers for turbulent exchange, and reduced lateral diffusivities are linked in a natural way by implementing mixing of potential vorticity and using a gauge term to insure that no spurious forces are introduced. It appears, therefore, possible to parameterise the appearance of zonal jets and its effect on the ventilation of interior ocean basins in non-eddy-resolving, realistic ocean models.