The injection of zonal momentum by buoyancy forcing in a Southern Ocean Model
Date
2015-01
Authors
Howard, Emma
Hogg, Andy
Waterman, Stephanie
Marshall, David P.
Journal Title
Journal ISSN
Volume Title
Publisher
American Meteorological Society
Abstract
An overturning circulation, driven by prescribed buoyancy forcing, is used to set a zonal volume transport in
a reentrant channel ocean model with three isopycnal layers. The channel is designed to represent the
Southern Ocean such that the forced overturning resembles the lower limb of the meridional overturning
circulation (MOC). The relative contributions of wind and buoyancy forcing to the zonal circulation are
examined. It is found that the zonal volume transport is strongly dependent on the buoyancy forcing and that
the eddy kinetic energy is primarily set by wind stress forcing. The zonal momentum budget integrated over
each layer is considered in the buoyancy-forced, wind-forced, and combined forcing case. At equilibrium,
sources and sinks of momentum are balanced, but the transient spinup reveals the source of momentum for
the current. In the buoyancy-forced case, the forcing creates a baroclinic shear with westward flow in the lower
layer, allowing topographic form stress and bottom friction to act as the initial sources of eastward momentum,
with bottom friction acting over a longer time frame. In the wind-forced and combined forcing cases,
the surface wind stress dominates the initial momentum budget, and the time to reach equilibration is shorter
in the combined forcing simulation. These results imply that future changes in the rate of formation of
Antarctic Bottom Water may alter the volume transport of the Antarctic Circumpolar Current.
Description
Keywords
Buoyancy, Circulation/Dynamics, Eddies, Geographic location/entity, Southern Ocean, Meridional overturning circulation, Topographic effects, Wind stress
Citation
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Source
Journal of Physical Oceanography
Type
Journal article