Antarctic oscillation

The Antarctic oscillation (AAO, to distinguish it from the Arctic oscillation or AO) is a low-frequency mode of atmospheric variability of the southern hemisphere. It is also known as the Southern Annular Mode (SAM). It is defined as a belt of westerly winds or low pressure surrounding Antarctica which moves north or south as its mode of variability.[1] In its positive phase, the westerly wind belt that drives the Antarctic Circumpolar Current intensifies and contracts towards Antarctica[2], while its negative phase involves this belt moving towards the Equator. Winds associated with the Southern Annular Mode cause oceanic upwelling of warm circumpolar deep water along the Antarctic continental shelf,[3][4] which has been linked to ice shelf basal melt,[5] representing a possible wind-driven mechanism that could destabilize large portions of the Antarctic Ice Sheet.[6]

In 2014, Dr Nerilie Abram used a network of temperature-sensitive ice core and tree growth records to reconstruct a 1000-year history of the Southern Annular Mode. This work suggests that the Southern Annular Mode is currently in its most extreme positive phase over at least the last 1000 years, and that recent positive trends in the SAM are attributed to increasing greenhouse gas levels and later stratospheric ozone depletion.[7][8]

See also


  1. Australian Bureau of Meteorology - The Southern Annular Mode. Accessed 25/10/2013.
  2. Thompson, David W. J.; Solomon, Susan; Kushner, Paul J.; England, Matthew H.; Grise, Kevin M.; Karoly, David J. (2011-10-23). "Signatures of the Antarctic ozone hole in Southern Hemisphere surface climate change". Nature Geoscience. 4 (11): 741–749. doi:10.1038/ngeo1296. ISSN 1752-0894.
  3. Hayakawa, Hideaki; Shibuya, Kazuo; Aoyama, Yuichi; Nogi, Yoshifumi; Doi, Koichiro (2012). "Ocean bottom pressure variability in the Antarctic Divergence Zone off Lützow-Holm Bay, East Antarctica". Deep Sea Research Part I: Oceanographic Research Papers. 60: 22–31. doi:10.1016/j.dsr.2011.09.005. ISSN 0967-0637.
  4. Spence, Paul; Griffies, Stephen M.; England, Matthew H.; Hogg, Andrew McC.; Saenko, Oleg A.; Jourdain, Nicolas C. (2014-07-12). "Rapid subsurface warming and circulation changes of Antarctic coastal waters by poleward shifting winds" (PDF). Geophysical Research Letters. 41 (13): 4601–4610. doi:10.1002/2014gl060613. hdl:1885/56321. ISSN 0094-8276.
  5. Greene, Chad A.; Blankenship, Donald D.; Gwyther, David E.; Silvano, Alessandro; Wijk, Esmee van (2017-11-01). "Wind causes Totten Ice Shelf melt and acceleration". Science Advances. 3 (11): e1701681. doi:10.1126/sciadv.1701681. ISSN 2375-2548. PMC 5665591. PMID 29109976.
  6. Anderson, R. F.; Ali, S.; Bradtmiller, L. I.; Nielsen, S. H. H.; Fleisher, M. Q.; Anderson, B. E.; Burckle, L. H. (2009-03-13). "Wind-Driven Upwelling in the Southern Ocean and the Deglacial Rise in Atmospheric CO2". Science. 323 (5920): 1443–1448. doi:10.1126/science.1167441. ISSN 0036-8075. PMID 19286547.
  7. "Data: 1000-year Southern Annular Mode reconstruction". National Climatic Data Center. Retrieved 18 August 2014.
  8. Abram, Nerilie (2014-05-11). "Evolution of the Southern Annular Mode during the past millennium". Nature. Retrieved 2014-09-13.

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