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Antarctic Circumpolar Transport and the Southern Mode: a Model Investigation of Interannual to Decadal Timescales : Volume 10, Issue 2 (10/04/2014)

By Hughes, C. W.

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Book Id: WPLBN0004020184
Format Type: PDF Article :
File Size: Pages 11
Reproduction Date: 2015

Title: Antarctic Circumpolar Transport and the Southern Mode: a Model Investigation of Interannual to Decadal Timescales : Volume 10, Issue 2 (10/04/2014)  
Author: Hughes, C. W.
Volume: Vol. 10, Issue 2
Language: English
Subject: Science, Ocean, Science
Collections: Periodicals: Journal and Magazine Collection, Copernicus GmbH
Historic
Publication Date:
2014
Publisher: Copernicus Gmbh, Göttingen, Germany
Member Page: Copernicus Publications

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Williams, J., De Cuevas, B. A., Coward, A. C., & Hughes, C. W. (2014). Antarctic Circumpolar Transport and the Southern Mode: a Model Investigation of Interannual to Decadal Timescales : Volume 10, Issue 2 (10/04/2014). Retrieved from http://worldlibrary.net/


Description
Description: School of Environmental Sciences, University of Liverpool, Liverpool, UK. It is well-established that, at periods shorter than a year, variations in Antarctic circumpolar transport are reflected in a barotropic mode, known as the southern mode, in which sea level and bottom pressure varies coherently around Antarctica. Here, we use two multidecadal ocean model runs to investigate the behaviour of the southern mode at timescales on which density changes become important, leading to a baroclinic component to the adjustment. We find that the concept of a southern mode in bottom pressure remains valid, and remains a direct measure of the circumpolar transport, with changes at the northern boundary playing only a small role even on decadal timescales. However, at periods longer than about 5 years, density changes start to play a role, leading to a surface intensification of the vertical profile of the transport. We also find that barotropic currents on the continental slope account for a significant fraction of the variability, and produce surface intensification in the meridional-integral flow. Circumpolar sea level and transport are related at all investigated timescales. However, the role of density variations results in a ratio of sea level change to transport which becomes larger at longer timescales. This means that any long-term transport monitoring strategy based on present measurement systems must involve multiplying the observed quantity by a factor which depends on frequency.

Summary
Antarctic circumpolar transport and the southern mode: a model investigation of interannual to decadal timescales

Excerpt
Allison, L. C., Johnson, H. L., and Marshall, D. P.: Spin-up and adjustment of the Antarctic Circumpolar Current and global pycnocline, J. Mar. Res., 69, 167–189, 2011.; Aoki, S.: Coherent sea level response to the Antarctic Oscillation, Geophys. Res. Lett., 29, 1950, doi:10.1029/2002GL015733, 2002.; Blaker, A. T., Hirschi, J. J.-M., McCarthy, G., Sinha, B., Taws, S., Marsh, R., Coward, A., and de Cuevas, B.: Historical analogues of the recent extreme minima observed in the Atlantic meridional overturning circulation at 26° N, Clim. Dynam., submitted, 2013.; Cunningham, S. A., Alderson, S. G., King, B. A., and Brandon, M. A.: Transport and variability of the Antarctic Circumpolar Current in Drake Passage, J. Geophys. Res., 108, 8084, doi:10.1029/2001JC001147, 2003.; Gnanadesikan, A. and Hallberg, R.: On the relationship of the circumpolar current to Southern Hemisphere winds in coarse-resolution ocean models, J. Phys. Oceanogr., 30, 2013–2034, 2000.; Gordon, A. L., Sprintall, J., Van Aken, H. M., Susanto, D., Wijffels, S., Molcard, R., Ffield, A., Pranowo, W., and Wirasantosa, S.: The I}ndonesian throughflow during 2004–2006 as observed by the {INSTANT program, Dyn. Atmos. Ocean., 50, 115–128, 2010.; Hibbert, A., Leach, H., Woodworth, P., Hughes, C. W., and Roussenov, V.: Quasi-biennial modulation of the Southern Ocean Coherent Mode, Q. J. Roy. Meteor. Soc., 136, 755–768, 2010.; Hughes, C. W. and Meredith, M. P.: Coherent sea level fluctuations along the global continental slope, Philos. T. Roy. Soc. Lond. A, 364, 885–901, doi:10.1098/rsta.2006.1744, 2006.; Hughes, C. W. and Stepanov, V. N.: Ocean dynamics associated with rapid J2 fluctuations: importance of circumpolar modes and identification of a coherent Arctic mode, J. Geophys. Res., 109 C06002, doi:10.1029/2003JC002176, 2004.; Hughes, C. W., Meredith, M. P., and Heywood, K.: Wind-driven transport fluctuations through Drake Passage: a Southern Mode, J. Phys. Oceanogr., 29, 1971–1992, 1999.; Hughes, C. W., Woodworth, P. L., Meredith, M. P., Stepanov, V., Whitworth, T., and Pyne, A.: Coherence of Antarctic sea levels, Southern Hemisphere Annular Mode, and flow through Drake Passage, Geophys. Res. Lett., 30, 1464, doi:10.1029/2003GL017240, 2003.; Kusahara, K. and Ohshima, K. I.: Dynamics of the wind-driven sea level variation around Antarctica, J. Phys. Oceanogr., 39, 658–674, doi:10.1175/2008JPO3982.1, 2009.; Olbers, D. and Lettmann, K.: Barotropic and baroclinic processes in the transport variability of the Antarctic Circumpolar Current, Ocean Dynam., 57, 559–578, doi:10.1007/s10236-007-0126-1, 2007.; Vivier, F., Kelly, K. A., and Harismendy, M.: Causes of large-scale sea level variations in the Southern Ocean: analyses of sea level and a barotropic model, J. Geophys. Res., 110, C09014, doi:10.1029/2004JC002773, 2005.; Weijer, W. and Gille, S. T.: Adjustment of the Southern Ocean to wind forcing on synoptic timescales, J. Phys. Oceanogr., 35, 2076–2089, doi:10.1175/JPO2801.1, 2005.; Woodworth, P. L., Vassie, J. M., Hughes, C. W., and Meredith, M. P.: A test of TOPEX/POSEIDON's ability to monitor flows through Drake Passage, J. Geophys. Res.-Oceans, 101, 11935–11947, 1996.; Zika, J., Le Sommer, J., Dufour, C., Naveira-Garabato, A., and Blaker, A.: Acceleration of the Antarctic Circumpolar Current by wind stress along the coast of Antarctica, J. Phys. Oceanogr.,

 

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