RECTIFICATION OF THE WIND-DRIVEN OCEAN CIRCULATION ON THE BETA-PLANE

A nonlinear Stommel model of the ocean circulation on the beta plane, driven by a time periodic wind stress, is investigated in order to stu dy symmetry properties of the observed time-mean ocean gyres. Due to t he presence of vorticity advection terms the model will have a steady or rectified response to fluctuating wind fields. In this paper a smal l inverse Ekman number, ''the small beta regime'', is considered. It i s demonstrated that for this case all qualitative features of the resi dual circulation, obtained numerically by Veronis (1970), are reproduc ed in an analytical way. They include the dipole character of the gyre , its maximum symmetry breaking around the north-south axis for interm ediate Reynolds numbers, measuring the ratio of vorticity forcing and dissipation, and the maximum residual response for intermediate forcin g frequencies.