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. In its positive phase, the westerly wind belt that drives the Antarctic Circumpolar Current intensifies and contracts towards Antarctica, 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, which has been linked to ice shelf basal melt, representing a possible wind-driven mechanism that could destabilize large portions of the Antarctic Ice Sheet. 

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.

See also
 North Atlantic oscillation
 Arctic oscillation
 Pacific decadal oscillation
 Anticyclone
 John Michael Wallace

References

External links 
 http://www.antarctica.ac.uk/met/gjma/sam.html Observation-based SAM index from 1957–present
 http://hurricane.ncdc.noaa.gov/pls/paleox/f?p=519:1:0::::P1_STUDY_ID:16197 1000-year Southern Annular Mode reconstruction
 Monthly Southern Hemisphere Annular Mode (SAM) Index or Antarctic Oscillation (AAO) Index 1850 - 2013
 Daily Southern Hemisphere Annular Mode (SAM) Index or Antarctic Oscillation (AAO) Index 1948 - 2013
 http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/aao/aao.loading.shtml
 https://web.archive.org/web/20081216220433/http://stratus.astr.ucl.ac.be/textbook//pdf/Chapter_5.pdf (chapter 5.2.3)
Animation of Southern Annular Mode in Victoria, Australia
 The Southern Annular Mode  Introduction to climate dynamics and climate modelling, Université catholique de Louvain

Category:Climate
Category:Climate of Antarctica
Category:Climate patterns
Category:Environment of Antarctica