Australian High: Difference between revisions

|caption = The high featuring aan [[anticlockwise]] rotation around an oval area of clear skies.

|area of occurrence=*[[Great Australian Bight]], in[[Western Australia]] and [[Southern Australia]] (summer)

The '''Australian High''', also known as the '''Great Australian Bightsubtropical Highridge''',<ref>[https://research.usq.edu.au/download/fdae9e258f6558b5a6ae795a319658f04a31869d3d2e7c1514de2f554db4bb25/3300249/Williams_Stone_IJC_2009_SV.pdf An assessment of relationships between the Australian subtropical ridge, rainfall variability and high-latitude circulation patterns] by Dr Allyson A.J. Williams and Dr Roger C. Stone. Queensland Climate Change Centre of Excellence, Nambour, Queensland.</ref> is a large, semi-permanent [[high pressure system|high pressure]] area or subtropical [[anticyclone]] that isseasonally foundvacillates onbetween the [[Great Australian Bight]] in [[Souththe Australia]],south overto the [[SouthernNorthern OceanTerritory]], betweenin 30the and 35 degrees of south latitudenorth.<ref>[https://earthobservatory.nasa.gov/images/78208/an-australian-anti-storm#:~:text=The%20weather%20system%20over%20the,high%20pressure%20near%20the%20surface. An Australian "Anti-storm"] EOS Project Science Office at NASA Goddard Space Flight Center. 5 June 2012.</ref> It is generally located between 25 and 40 degrees of south latitude, depending on the season.<ref>[https://www.bushwalkingleadership.org.au/resource/summary-of-weather-terms/ Summary of Weather Terms] Bushwalking Leadership. Retrieved 7 April 2022.</ref> In summer, it generally sits over [[southern Australia]], providing mostly dry weather. In winter it normally moves north, thus permitting [[cold front]]s and [[low pressure system]]s to relocate up from the Southern Ocean and bring rainfall to southern Australia.<ref name = BOM>[http://www.bom.gov.au/climate/updatesabout/articles/a025.shtml#:~:text?bookmark=stridge The%20subtropical%20ridge%20is%20a,on%20the%20climate%20of%20Australia. SubtropicalSub-tropical ridge leaves us high and dry this JuneRidge] [[Bureau of Meteorology]]. JulyRetrieved May 31, 2017.2023</ref>

[[File:High Pressure.jpg|thumb|left|The Australian High west of Tasmania over the [[Indian Ocean]]]]

The Australian High tends to follow the seasonal variation in [[position of the sun]]; it is strongest and most persistent during the southern hemisphere summer and weakest during winter when it shifts towards the interior of Australia, as the [[westerlies|westerly]] [[frontal system]]s becomes more active in the region around the Bight, thereby allowing [[Cold front|cold fronts]] and [[Low-pressure area|low-pressure systems]] to perforate the southern states.<ref name = prevention>[https://www.preventionweb.net/news/stalled-weather-how-stuck-air-pressure-systems-drive-floods-and-heatwaves STALLED WEATHER: HOW STUCK AIR PRESSURE SYSTEMS DRIVE FLOODS AND HEATWAVES] by Steve Turton from PreventionWeb.net. 3 March 2022</ref> This high-pressure block exhibits anticyclonic behaviour, circulating the air clockwise. It remains almost stationary for an prolonged period over the Bight, hence obstructing the typical easterly procession of weather systems across southern Australia.<ref>[https://www.abc.net.au/news/2018-08-14/southern-annular-mode-and-how-it-affects-our-weather/10106134 Southern Annular Mode: The climate 'influencer' you may not have heard of] By Kate Doyle from [[ABC TV (Australian TV channel)|ABC]]. 14 August 2018. Retrieved 7 April 2022.</ref>

[[File:Australia.A2002231.0145.250m NASA Nullarbor.jpg|thumb|230px|The Highhigh tends to keep the southern half of Australia mostly clear and dry.]]

The anticyclonic circulation produces a dry climate, bringing warm to hot weather in the southern Australian summer. The high influences the weather and climatic patterns of vast areas of [[Australia]]; The aridity of the [[deserts of Australia|Australian deserts]] and the summer [[drought in Australia|drought]] of southern Australia is due to the large-scale subsidence and sinking motion of air in the system.<ref>[https://www.weatherzone.com.au/news/extreme-heat-on-its-way-to-northwest-wa/536209 Extreme heat on its way to northwest WA] by Ben Domensino from [[Weatherzone]]. 12 February 2022. Retrieved 7 April 2022.</ref> In winter, when the high remains stationary in the Bight (due to a positive [[Southern Annular Mode|SAM]] phase), it can block or replace [[cold front]]s from the Southern Ocean, thereby allowing warm weather to the southeast.<ref>[https://www.weatherzone.com.au/news/sydneys-record-15-day-spell-of-20-degree-winter-days/534824 Sydney's record 15-day spell of 20 degree winter days] by Ben Domensino from Weatherzone. 23 August 2021</ref>

In the western part of the high, hot dry northerly winds from the dry centre push through South Australia and Victoria, ensuing heatwave conditions in these regions. Conversely,The theAustralian High mayis directone morethe rainfalldrivers inof southeastthe Australia[[Southerly buster]], aswhich feeble westerly winds resultoccurs in increasethe ofsoutheast easterlycoast onshorein windsthe thatsummer.<ref>''Modelling bringcoastally moisttrapped airwind fromsurges theover TasmanSoutheastern SeaAustralia.'' towardsReid, theHelen eastJ. coast from1999. [[BrisbaneUNSW]]</ref> toIn [[Sydney]]winter, (thoughwhen regionsthe westhigh ofpressure system is broad over the [[GreatAustralia]]n landmass, Dividingwidespread Range[[frost]] wouldmay remain dry)occur.<ref name = BOM/><ref>[https://physwww.abc.net.orgau/news/20192023-0105-stubborn27/widespread-highfrost-pressureoutbreak-forecast-australia-heatwaves.htmlbom/102399008 TheFrost stubbornexpected high-pressureacross systemnearly behindevery state and territory in Australia's recordthis heatwavesweekend] byBy SteveTyne TurtonLogan from [[TheABC ConversationNews (websiteAustralia)|TheABC ConversationNews]]. 2527 JanuaryMay 20192023. Retrieved 7 April 2022.</ref> The Australian High is one the drivers of the [[Southerly buster]], which occurs in the southeast coast.<ref>''Modelling coastally trapped wind surges over Southeastern Australia.'' Reid, Helen J. 1999. [[UNSW]] </ref>

===LocationsEffects on Asia===

Between summer and autumn, the high over thesouthern Great Australian BightAustralia may be linked, or would intertwine, with the Tasman High in the southern [[Tasman Sea]]. (between [[Tasmania]] andWhen the [[Southhigh Island]]stalls of [[New Zealand]]). Whenin the highTasman stallsSea and becomes a [[blocking high]], New Zealand and [[climate of Tasmania|Tasmania]] will generally experience warm and generally dry weather, whilst the east coast of Australia (particularly southern Queensland and New South Wales) will experience moist onshore flows, includingparticularly heavyduring rain events, and lack of warm days (more often duringa [[La NinaNiña]] phases)phase.<ref>[http://www.bom.gov.au/climate/current/statements/scs64.pdf Special Climate Statement—record warmth in the Tasman Sea, New Zealand and Tasmania] Bureau of Meteorology. 27 March 2018</ref> In [[2021 Eastern Australian floods|March 2021]], and also in [[2022 Easterneastern Australia floods|February and March 2022]], a stubborn blocking high in the Tasman caused heavy rain and flooding over large parts of Southeast Queensland and coastal New South Wales.<ref name = prevention/><ref>[https://docs.niwa.co.nz/library/public/NIWAsts71.pdf THE CLIMATE AND WEATHER OF NELSON AND TASMAN] 2nd edition G. R. Macara </ref> A blocking high in the southern Tasman Sea wards off low pressure systems and troughs out in the Tasman Sea towards eastern Australia, whereby providing rainfall on the east coast of Australia.<ref>[https://www.stuff.co.nz/national/weather-news/124327154/weather-blocking-high-expected-to-keep-much-of-country-warm-mostly-dry-for-last-days-of-summer Weather: Blocking high expected to keep much of country warm, mostly dry for last days of summer] by Michael Daly from [[Stuff (website)|Stuff]]. February 23 2021.</ref>