Semi-Adiabatic Model of the Deep Stratification and Meridional Overturning
Abstract
An analytical model of the Atlantic deep stratification and meridional overturning circulation is presented
that illustrates the dynamic coupling between the Southern Ocean and the midlatitude gyres. The model,
expressed here in terms of the two-and-a-half-layer framework, predicts the stratification and meridional
transport as a function of the mechanical and thermodynamic forcing at the sea surface. The approach is based
on the classical elements of large-scale circulation theory—ideal thermocline, inertial western boundary
currents, and eddy-controlled Antarctic Circumpolar Current (ACC) models—which are combined to produce
a consistent three-dimensional view of the global overturning. The analytical tractability is achieved by
assuming and subsequently verifying that the pattern of circulation in the model is largely controlled by
adiabatic processes: the time-mean and eddy-induced isopycnal advection of buoyancy. The mean stratification
of the lower thermocline is determined by the surface forcing in the ACC and, to a lesser extent, by the
North Atlantic Deep Water formation rate. Although the vertical small-scale mixing and the diapycnal eddyflux
components can substantially influence the magnitude of overturning, their effect on the net stratification
of the midlatitude ocean is surprisingly limited. The analysis in this paper suggests the interpretation of the
ACC as an active lateral boundary layer that does not passively adjust to the prescribed large-scale solution
but instead forcefully controls the interior pattern.
Description
The article of record as published may be found at http://dx.doi.org/10.1175/2010JPO4538.1
Rights
This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.Collections
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