VORTICITY DYNAMICS AND ZONALLY AVERAGED OCEAN CIRCULATION MODELS

Diagnostic equations relating the zonally averaged overturning circula tion to north-south density variations are derived and used to determi ne a new closure scheme for use in zonally averaged ocean models. The presentation clarifies the dynamical link between vorticity dissipatio n in the western boundary layer and the meridional overturning circula tion and provides insight into the relevance and limitations of zonall y averaged models. The new closure scheme is substantially different f rom that introduced by Wright and Stocker. In particular, it includes nonlocal effects, which are potentially important. The model formulati on results in a solution with three free parameters. A parameter repre senting 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 cir culation 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 exami ned. The derivation and model tests give additional support for the us e of zonally averaged models in studies of the climate system.