On the time‐averaged flow of quasi‐geostrophic wind‐driven gyres

The time‐averaged flow of a three‐layer eddy‐resolving quasi‐geostrophic ocean model is considered in the light of two analytical models of wind‐driven gyres, in which the vertical structure of the gyre is set by assuming that potential vorticity is uniform beneath layers exposed to forcing. The first, due to Young and Rhines (1982), supposes that the depth‐integrated meridional transport is set by the imposed wind‐stress curl. In contrast, in the baroclinic Fofonoff gyres of Marshall and Nurser (1986, 1988), inertial aspects of the flow are emphasized without imposing a Sverdrup constraint. The mean fields from the model are seen to lie between the two extremes represented by these analytical solutions. In the interior of the gyre away from inertial boundary currents and jets, the Sverdrup constraint is obeyed, and the mean flows resemble the Young and Rhines solution. However, the essential character of the overspun recirculation, including the weakly depth‐dependent nature of the currents in its return flow, seem to be well captured in the inertial limit considered by Marshall and Nurser.