A Simple Model of the Warm-water Branch of Meridional Overturning

A reduced-gravity model is presented of the warm-water branch of the mid-depth meridional overturning circulation in a rectangular basin with a circumpolar connection. The model describes the balance between production of warm water by Ekman advection across the circumpolar current, dissipation of water water by eddy fluxes southward across the current, and the net production or dissipation of warm water by diabatic processes north of the current. Analytical solutions are obtained for weak friction and diabatic forcing. The results emphasize the role of the eastern boundary condition in setting the thermocline structure north of the current, and the nonlinear interactions between wind forcing, eddy fluxes, and diabatic mixing, which together control the structure and amplitude of the model meridional overturning circulation.