The Australian High, also known as the Great Australian Bight High, is a semi-permanent high pressure area or subtropical anticyclone that is found on the Great Australian Bight in South Australia, over the Southern Ocean, between 30 and 35 degrees of south latitude.[1][2] In summer, it generally sits over southern Australia, providing mostly dry weather. In winter it normally moves north, thus permitting cold fronts and low pressure systems to relocate up from the Southern Ocean and bring rainfall to southern Australia.[3]
| Australian High | |
|---|---|
 The high featuring a anticlockwise rotation around an oval area of clear skies. | |
| Area of occurrence | Great Australian Bight in Southern Australia |
| Season | November–May |
| Effect |
|
Description
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 westerly frontal systems becomes more active in the region around the Bight, thereby allowing cold fronts and low-pressure systems to perforate the southern states.[4] 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.[5]
The High can stretch thousands of kilometers across the Bight, and may move eastwards towards Tasmania. This area of high pressure is part of the great subtropical belt of anticyclones called the subtropical ridge. A cloud hole with an expansion as far as 1,000 kilometers (620 miles) has been observed, with tops of 1,040 millibars. The high may be extensive enough to interconnect with the Tasman High over in the Tasman Sea, just near New Zealand.[6]
Effects
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 Australian deserts and the summer drought of southern Australia is due to the large-scale subsidence and sinking motion of air in the system.[7] In winter, when the high remains stationary in the Bight (due to a positive SAM phase), it can block or replace cold fronts from the Southern Ocean, thereby allowing warm weather to the southeast.[8]
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 High may direct more rainfall in southeast Australia, as feeble westerly winds result in increase of easterly onshore winds that bring moist air from the Tasman Sea towards the east coast from Brisbane to Sydney (though regions west of the Great Dividing Range would remain dry).[3][9] The Australian High is one the drivers of the Southerly buster, which occurs in the southeast coast.[10]
Standorte
Cities and towns with a Mediterranean climate in southern Australia are most affected by the High during the summer; from Perth and Esperance in Western Australia to Adelaide and Mount Gambier in South Australia and Hamilton in Victoria, and as well as those with a semi-arid climate; Kalgoorlie and Eucla in Western Australia to Ceduna, Renmark and Port Pirie in South Australia. Some inland towns in New South Wales westwards of the Great Dividing Range, such as Wagga Wagga and Albury in the Riverina, and as well as those in Victoria, such as Horsham, Bendigo and Mildura, may also experience the dry effects of the High in the summer due to their more westward position and relatively close vicinity to the system.[11]
Tasman High
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). When the high stalls in the Tasman Sea and becomes a blocking high, 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 (though more often during a La Niña phase).[12] In March 2021, and also in 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.[4][13] 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.[14]
See also
References
- ^ An Australian "Anti-storm" EOS Project Science Office at NASA Goddard Space Flight Center. 5 June 2012.
- ^ Summary of Weather Terms Bushwalking Leadership. Retrieved 7 April 2022.
- ^ a b Subtropical ridge leaves us high and dry this June Bureau of Meteorology. July 2017.
- ^ a b STALLED WEATHER: HOW STUCK AIR PRESSURE SYSTEMS DRIVE FLOODS AND HEATWAVES by Steve Turton from PreventionWeb.net. 3 March 2022
- ^ Southern Annular Mode: The climate 'influencer' you may not have heard of By Kate Doyle from ABC. 14 August 2018. Retrieved 7 April 2022.
- ^ High pressure systems: everything you need to know by Ben Domensino from Weatherzone. 21 May 2018. Retrieved 22 April 2022.
- ^ Extreme heat on its way to northwest WA by Ben Domensino from Weatherzone. 12 February 2022. Retrieved 7 April 2022.
- ^ Sydney's record 15-day spell of 20 degree winter days by Ben Domensino from Weatherzone. 23 August 2021
- ^ The stubborn high-pressure system behind Australia's record heatwaves by Steve Turton from The Conversation. 25 January 2019. Retrieved 7 April 2022.
- ^ Modelling coastally trapped wind surges over Southeastern Australia. Reid, Helen J. 1999. UNSW
- ^ THE CLIMATE KELPIE BLOG: Where have our winters gone? by Climate Kelpie. 6 May 2020.
- ^ Special Climate Statement—record warmth in the Tasman Sea, New Zealand and Tasmania Bureau of Meteorology. 27 March 2018
- ^ THE CLIMATE AND WEATHER OF NELSON AND TASMAN 2nd edition G. R. Macara
- ^ Weather: Blocking high expected to keep much of country warm, mostly dry for last days of summer by Michael Daly from Stuff. February 23 2021.