Vorticity Dynamics and Zonally Averaged Ocean Circulation Models

Abstract

Diagnostic equations relating the zonally averaged overturning circulation to north?south density variations are derived and used to determine a new closure scheme for use in zonally averaged ocean models. The presentation clarifies the dynamical link between vorticity dissipation in the western boundary layer and the meridional overturning circulation and provides insight into the relevance and limitations of zonally averaged models. The new closure scheme is substantially different from that introduced by Wright and Stocker. In particular, it includes nonlocal effects, which are potentially important. The model formulation results in a solution with three free parameters. A parameter representing the damping associated with meridional velocity gradients has very little effect on the solution and could be set to zero. The other two are used to tune the model to agree with results of a general circulation model. Good agreement is achieved for values consistent with expectations. The closure scheme is implemented in the model of Wright and Stocker, and the sensitivity to the new model parameters is examined. The derivation and model tests give additional support for the use of zonally averaged models in studies of the climate system.