Sverdrup Balance and Three Dimensional Variability of the Meridional Overturning Circulation

Thomas, Matthew (2012) Sverdrup Balance and Three Dimensional Variability of the Meridional Overturning Circulation. Doctoral thesis, University of East Anglia.

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Abstract

Abstract
Two numerical models are used to gain an understanding of the spatial
structure of Atlantic Meridional Overturning Circulation changes and the
dynamical framework within which those changes occur.
Sverdrup balance is studied using the 16 year ECCO-GODAE state estimation.
It is shown to hold well in the interior subtropics when integrating
to a mid-depth level and when considered at spatial scales larger than approximately
5◦. Outside of the subtropics, in western boundary currents
and at short spatial scales, significant departures occur mostly due to a
failure in the assumption that there is a level of no motion that can be
integrated to and partly due to the assumption of linear vorticity. Sverdrup
balance is reached when enough time is allowed for the ocean to adjust to
forcing by the propagation of baroclinic Rossby waves.
A climate change simulation of the HiGEM high resolution coupled climate
model is used to investigate to what extent a 30% reduction in the
deep southward transport is balanced by a reduction in the northward flowing
surface western boundary transport, or an increase in the southward
upper interior transport. It is found that a reduction in the southwards
deep transport is balanced solely by a weakening of the northward surface
western boundary current. This is consistent with Sverdrup balance holding
to a good approximation in the basin interior.
Overturning calculations in depth space and density space are found to
differ within the subpolar gyre of a 120 year Control simulation of HiGEM.
Depth space overturning is found to depend strongly on the transports of
the Labrador current, which are strengthened by a spin-up of the horizontal
subpolar gyre. Density space overturning is found to be strongly
dependent on the densities of the Labrador Current, which increase following
Labrador Sea water mass transformation and strong flow through the
Denmark Straits.

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Science > School of Environmental Sciences
Depositing User:	Users 2259 not found.
Date Deposited:	07 Mar 2014 11:43
Last Modified:	07 Mar 2014 11:43
URI:	https://ueaeprints.uea.ac.uk/id/eprint/48025
DOI:

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