Dispersive-dissipative eddy parameterization in a barotropic model

Recently a new class of coarse-grained equations, known as a models, have b een proposed for the mean motion of an ideal incompressible fluid. The use of one such model to represent the time-mean component of a turbulent beta -plane circulation characterized by potential vorticity mixing is considere d. In particular, the focus is on the wind-driven circulation in a shallow ocean basin, a problem well studied as a prototype of more realistic ocean dynamics. The authors demonstrate the ability of an alpha model to reproduc e qualitatively the structure of a four-gyre circulation that forms (in the time mean) when the barotropic vorticity equation is driven by a symmetric , double-gyre wind forcing, and when the dissipation is weak. This is offer ed as a first step in assessing the utility of the alpha -model approach to simulating more complex geophysical flows.