Eddy saturation of the Southern Ocean: a baroclinic versus barotropic
perspective
Abstract
“Eddy saturation” is the regime in which the total time-mean volume
transport of an oceanic current is relatively insensitive to the wind
stress forcing and is often invoked as a dynamical description of
Southern Ocean circulation. We revisit the problem of eddy saturation
using a primitive-equations model in an idealized channel setup with
bathymetry. We apply only mechanical wind stress forcing; there is no
diapycnal mixing or surface buoyancy forcing. Our main aim is to assess
the relative importance of two mechanisms for producing eddy saturated
states: (i) the commonly invoked baroclinic mechanism that involves the
competition of sloping isopycnals and restratification by production of
baroclinic eddies, and (ii) the barotropic mechanism, that involves
production of eddies through lateral shear instabilities or through the
interaction of the barotropic current with bathymetric features. Our
results suggest that the barotropic flow-component plays a crucial role
in determining the total volume transport.