Mesoscale Eddy Parameterizations Using a Residual Scheme

The effects of mesoscale eddies are commonly parameterized by adding along-isopycnal eddy advection (skew flux) in ocean interior and horizontal eddy flux in top boundary into tracer equations (i.e. Gent-McWilliams parameterization). Here we present some results using a scheme based on the transformed Eulerian mean (TEM), or residual, framework. This scheme is distinguished from the traditional parameterization in that it uses the residual velocity (the sum of Eulerian-mean velocity and eddy velocity) as the prognostic valuable for model integration, and no eddy parameterization is required in tracer equations.

We compare the scheme both to traditional parameterizations, and to eddy-permitting calculations. We pay particular attention to the different formulations of the the residual scheme in the boundary layer (sometimes known as 'tapering'). For example, we study the dependence on the boundary layer depth, the effects on capping the maximum permitted value for the eddy diffusivity, and the role of an enhanced horizontal diffusivity in the upper layers. We also explore the performance of the scheme when multiple tracers are present, and the effects of bottom topography.