Australian High: Difference between revisions

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 fronts and 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>

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 [[blocking high|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>

Between summer and autumn, the high over the Great Australian Bight may be linked, or would intertwine, with the Tasman High in the southern [[Tasman Sea]], between [[Tasmania]] and the [[South Island]] of [[New Zealand]], where it can become a [[blocking high]]. During such events, New Zealand and 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, including heavy rain events, and lack of warm days.<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 Eastern 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> These blocking highs ward off low pressure systems out in the Tasman Sea and towards eastern Australia, whereby providing rainfall on the east coast of Australia (particularly during [[La Nina]] phases).<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>