It is a climate driver forAustralia, influencing the country's weather conditions – It is associated with storms andcold fronts that move from west to east that bring precipitation to southern Australia.[3]
SAM from 1979 to 2020.The westerly wind belt during its negative phase, as it expands towards southeastern Australia.[4]
Both positive and negative SAM events tends to last for approximately ten days to two weeks, though the timeframe between a positive and a negative event is random. It is usually in the span of a week to a few months, with a negative SAM being more common in the cool months and a positive SAM being more prolonged in the warmer months. Winds associated with the Southern Annular Mode cause oceanicupwelling of warm circumpolar deep water along the Antarctic continental shelf,[5][6] which has been linked toice shelf basal melt,[7] representing a possible wind-driven mechanism that could destabilize large portions of theAntarctic ice sheet.[8]
In its positive phase, the westerly wind belt that drives theAntarctic Circumpolar Current intensifies and contracts towardsAntarctica.[9] In winter, a positive phase increases rainfall (includingEast coast lows) in south-eastern Australia (aboveVictoria) due to higher onshore flows from thePacific Ocean, decreases rain in the south-west, and decreases snow in thealpine areas. In spring and summer, a positive phase reduces the chance of extreme heat and increases humid onshore flows, therefore making spring and summer wetter than normal. A positive phase would usually occur more frequently with aLa Niña event.[10]
Its negative phase involves the belt moving towards theequator, whereby decreasing rainfall in the southeast of Australia in the summer and as well as raising the possibility of springheatwaves. Moreover, winters will usually be wetter than normal in the south and southwest with more snowfall in the alpine areas, but drier in the east coast due to less moist onshore flows from the east andblockage ofcold fronts by theGreat Dividing Range, which would act as arain shadow. This phase will usually be more frequent with anEl Niño event.[10]
In 2014,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 increasinggreenhouse gas levels and laterstratosphericozone depletion.[11][12]
^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.Bibcode:2012DSRI...60...22H.doi:10.1016/j.dsr.2011.09.005.ISSN0967-0637.
^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.Bibcode:2011NatGe...4..741T.doi:10.1038/ngeo1296.ISSN1752-0894.S2CID40243634.
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