Analytical solutions for the ACC and its overturning circulation
Abstract
An explicit analytical model of the Antarctic Circumpolar Current (ACC) is presented in which the
key feature is the balance between the Eulerian circulation acting to overturn the isopycnals and
geostrophic eddies which tend to flatten them. Solutions for the stratification and overturning
circulation are obtained by expanding the governing residual mean equations of motion in a small
parameter (ε) which measures the relative strength of the surface buoyancy flux and mechanical
forcing by winds. Our balanced asymptotic model extends and reconciles the earlier views on the
dynamics of the (streamwise-averaged) ACC by demonstrating that the zero order balance between
the eddy-induced circulation and the mean flow determines gross features of the buoyancy
distribution in the interior of the ACC. The diabatic buoyancy fluxes are essential in driving the
secondary (residual) circulation which is, however, largely steered along the pathways set by the
dominant adiabatic balance. Model assumptions are supported by a close agreement of the analytical
solutions and fully nonlinear numerical calculations.
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