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Equilibration of the Antarctic Circumpolar Current by Standing Meanders

Thompson, Andrew F. and Naveira Garabato, Alberto C. (2014) Equilibration of the Antarctic Circumpolar Current by Standing Meanders. Journal of Physical Oceanography, 44 (7). pp. 1811-1828. ISSN 0022-3670. http://resolver.caltech.edu/CaltechAUTHORS:20140815-144545467

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Abstract

The insensitivity of the Antarctic Circumpolar Current (ACC)’s prominent isopycnal slope to changes in wind stress is thought to stem from the action of mesoscale eddies that counterbalance the wind-driven Ekman overturning—a framework verified in zonally symmetric circumpolar flows. Substantial zonal variations in eddy characteristics suggest that local dynamics may modify this balance along the path of the ACC. Analysis of an eddy-resolving ocean GCM shows that the ACC can be broken into broad regions of weak eddy activity, where surface winds steepen isopycnals, and a small number of standing meanders, across which the isopycnals relax. Meanders are coincident with sites of (i) strong eddy-induced modification of the mean flow and its vertical structure as measured by the divergence of the Eliassen–Palm flux and (ii) enhancement of deep eddy kinetic energy by up to two orders of magnitude over surrounding regions. Within meanders, the vorticity budget shows a balance between the advection of relative vorticity and horizontal divergence, providing a mechanism for the generation of strong vertical velocities and rapid changes in stratification. Temporal fluctuations in these diagnostics are correlated with variability in both the Eliassen–Palm flux and bottom speed, implying a link to dissipative processes at the ocean floor. At larger scales, bottom pressure torque is spatially correlated with the barotropic advection of planetary vorticity, which links to variations in meander structure. From these results, it is proposed that the “flexing” of standing meanders provides an alternative mechanism for reducing the sensitivity of the ACC’s baroclinicity to changes in forcing, separate from an ACC-wide change in transient eddy characteristics.


Item Type:Article
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http://journals.ametsoc.org/doi/abs/10.1175/JPO-D-13-0163.1PublisherArticle
http://dx.doi.org/10.1175/JPO-D-13-0163.1DOIArticle
Additional Information:© 2014 American Meteorological Society. Manuscript received 24 July 2013, in final form 19 March 2014. AFT gratefully acknowledges support from the National Science Foundation (OCE-1235488), and ACNG support from a Philip Leverhulme Prize. Development of the ideas in this study have benefited from conversations with Ryan Abernathey, Toby Bischoff, Stuart Bishop, Chris Hughes, Kurt Polzin, Andrew Stewart, and Jan Zika. We thank Andy Hogg and an anonymous reviewer for comments that significantly improved this manuscript.
Funders:
Funding AgencyGrant Number
NSFOCE-1235488
Philip Leverhulme PrizeUNSPECIFIED
Subject Keywords:Geographic location/entity, Southern Ocean, Circulation/ Dynamics, Fluxes, Mesoscale processes, Stationary waves, Topographic effects, Physical Meteorology and Climatology, Vorticity
Record Number:CaltechAUTHORS:20140815-144545467
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20140815-144545467
Official Citation:Andrew F. Thompson and Alberto C. Naveira Garabato, 2014: Equilibration of the antarctic circumpolar current by standing meanders. J. Phys. Oceanogr., 44, 1811–1828. doi: http://dx.doi.org/10.1175/JPO-D-13-0163.1
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:48631
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:15 Aug 2014 22:06
Last Modified:16 Aug 2014 01:59

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