Two-layer rotating hydraulics: Strangulation,remote and virtual controls

The hydraulics of two-layer, rotating channel flow is examined in the limit where the channel width is large compared to the internal Rossby radius of deformation, but small compared to the external deformation radius. In this limit the baroclinic flow is contained in boundary layers along each side wall, while the barotropic flow is distributed over the width of the channel. Width variations along the channel cause the strength of the barotropic flow to vary and the barotropic variations influence the baroclinic boundary layers in two independent ways. The dual nature of this forcing gives rise to a new type of critical condition which we refer to as a remote control. Virtual and narrows controls also arise. Steady solutions can be obtained by solving a pair of simple quadratic equations and examples are given showing various combinations of controls.Woods Hole Oceanographic Institution Contribution No. 7252.