Barotropic response to cooling

Abstract

Imposed horizontal density differences in a nonrotating fluid generate vertical circulation which has vanishing vertically integrated transports. When the system is rotating, geostrophic velocities can balance the density differences and the vertically integrated transports need not vanish locally. In a two-layer fluid, fin ite amplitude disturbances lead to barotropic flows that have the same direction as the velocity in the layer that thickens as a result of the disturbance. Specific calculations are carried out for the geostrophic adjustment model in situations that approximate those in which 18° water is formed south of the Gulf Stream. The upper layer transport that results from sudden cooling (as simulated by density differences that are initially unbalanced geostrophically) is in the same direction as the Gulf Stream transport and comparable to it in magnitude. A lower level transport of the same magnitude flows in the opposite direction with a maximum value about an internal radius of deformation to the right of that of the upper layer. The barotropic transport is about 1/ 5 as large and flows downstream in the Gulf Stream and upstream to the right of the Gulf Stream.