Southerly Buster

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Arrival of a southerly buster in Sydney, over the Royal National Park.

A Southerly Buster is the colloquial name of an abrupt southerly wind change in the southern coastal regions of New South Wales and Victoria, Australia which approaches from the southeast mainly in a hot day, bringing in cool, usually storm-laden conditions, and a dramatic temperature drop, thus ultimately replacing and relieving the prior hot conditions.[1] Marking the boundary between hot and cool air masses, a southerly buster is often represented by a roll-up cloud perpendicular to the coast, which appears from the south and coexist with the wind change, though normally there is little visual signal of the southerly's arrival.[2]

Southerly busters occur about 32 times each year on the coast of southeastern Australia, with variable strength, usually in spring and summer. Although southerly busters are oftentimes associated with NSW and Victoria, they would also betide the east coast of Tasmania, New Zealand, Argentina and Chile.[3] They are known as ‘backdoor fronts’ in North America, and ‘Spanish plumes’ in Europe.[4]

History[edit]

On hot afternoons in the late nineteenth century, before the days of radio, the Sydney Observatory would fly a flag bearing the letters "JB" to indicate that the southerly buster had reached Jervis Bay, about 150 km to the south as the crow flies.[5] The people of Sydney greeted the arrival of the southerly buster after a hot summer day. During the early days of the European settlement, Sydney's summer storms were accompanied by rolling red dust from the colony's brickworks.[6] In 1879, George Herbert Gibson published a book called Southerly Busters, where a buster wreaks havoc near Hyde Park, Sydney. Author Ruth Park makes a reference to the southerly buster in her novel Poor Man's Orange (1949):[6]

After an unbearably hot day, the old men on the balconies were sniffing the air and saying, 'Here she comes!' The Southerly Buster, the genie of Sydney, flapped its coarse wing over the city ... The women undid the fronts of their frocks and the little children lifted up their shirts and let it blow on their sweaty bottoms.

Formation[edit]

For a southerly buster to occur, a cold front approaching the southeast of Australia should lie between two high pressure systems; one in the Tasman Sea and the other in the Great Australian Bight.[7]

On a hot day, a strong offsea gale develops from the south usually in the late afternoon and early evening, causing a rapid fall in temperature as it arrives, and sometimes a short but violent rain or hail storm, thunderstorms and/or lightning, with the strongest winds being at the leading edge of the buster. However, the southerly buster does not always create precipitation, aside from light drizzle.[8] It is proposed that the southerly buster is basically a coastal gravity current that is held against the mountains by the Coriolis force and in transverse geostrophic balance, and is generated when a cold front is obstructed, experiencing anticyclonic distortion near the Great Dividing Range, spreading northward as a coastal trapped orographic jet.[9]

The southerly buster is caused by its interaction with the Great Dividing Range, as the cool air becomes trapped against the ranges, oftentimes in the Gippsland area of Victoria, where the mountains create a channelling effect as the southerly winds move across the New South Wales coast. When the inland portion of the cold front is held against the mountains, the part over the sea proceeds to move along the shore, twisting the front into an 'S' shape. This activity continues on the southern New South Wales coast, while areas leading the front are still experiencing hot northwesterly winds.[10]

Characteristics[edit]

The main distinguishing feature of a southerly buster is the sudden, squally southerly change in wind direction which replace the continental northwesterly winds.[11] This is accompanied by a marked temperature drop and sea level pressure rise. Wind gusts in excess of 40 knots (74 km/hour) near ground level averages about three per year, which usually come about after very hot days and would tremendously ease within 30 to 60 minutes after the Buster's arrival, becoming rather light within a few hours. A regular Southerly Buster is between 20 and 60 nautical miles wide, with the heavier winds concentrated on the seaward strip, with its depth being around 1000m, restricted by the height of the mountains to west.[12][13]

An orographic jet, the southerly buster is clearly a mesoscale phenomenon, developing on about one day. Because busters seldom keep a staunch speed while advancing along the coast, its arrival has always been difficult to foretell, though meteorologists nowadays have the gain of satellite imagery and weather radar to foresee it, with wind warning issued by the Bureau of Meteorology. Temperature changes can be dramatic, with falls of 10 °C (50 °F) to 15 °C (59 °F) often occurring in a few minutes.[14] In extreme conditions, especially in Melbourne, a southerly buster may lower the temperatures from 40 °C (104 °F) to 19 °C (66 °F).[15]

Regions[edit]

  • In New South Wales, southerly busters generally reach their maximum intensity between Nowra and Newcastle, and would tend to extend up the New South wales coast from Gabo Island to just north of Port Macquarie – They rarely pass beyond that northern limit, and when they do they are usually strengthened by the presence of a tropical cyclone off the north coast of New South Wales.[16] Sydney receives an average of about five Southerly Busters a year, with the stronger ones generally reaching Sydney in the late afternoon or early evening on a hot day, though at times it would arrive after several days of hot weather. It is a crucial weather feature in the Sydney area, particularly for yachtsmen. [10]
  • In Victoria, most notably in Melbourne, southerly busters occur during the afternoons where the domineering heat, brought on by north-westerly winds from central Australia, suddenly gives way to a rapid drop in temperature, followed by rain, thunderstorms and a relatively cool night. Temperature drops in these parts of Victoria are more dramatic than those in the east coast of New South Wales, where a 10 °C (50 °F) drop can occur within half an hour.[17] Southerly busters most emerge in spring, as the landmass northbound of Melbourne starts to warm up. Meanwhile though, the Southern Ocean, which provides cool breezes to Victoria from the west, does not warm up as swiftly as the mainland. As such, the temperature difference between hot air from the north and cold from the ocean would be very great, thus providing good conditions for the formation of thunderstorms.[18]
  • In Wellington, New Zealand these storms are normally short and frequently have winds gusting between 120 km/h and 160 km/h though higher speeds are known.
  • In South America, these southerly fronts frequently encroach on the southern coast of Chile and Argentina and would then advance northwards on both sides of the Andes.[19]

Records[edit]

The strongest recorded Southerly Buster befell at 6.40 pm on 18 December 1948 in Sydney Airport, with a maximum gust of 61 knots (113 km/h). The strongest gust recorded along the NSW coast outside of Sydney was 70 knots (130 km/h) at Port Kembla on 20 November 1973.[10]

Incidents[edit]

On November 21st 2016, at around 6pm, a powerful southerly change occurred in Melbourne, which resulted in the death of 10 people, who were asthmatic and succumbed to respiratory failure.[21] Thousands of others across the city experienced allergic reactions and asthma-like symptoms triggered by the storm.[22] This was due to a stark southerly wind (60 km/hour) that distributed ryegrass pollen into the moist air, rupturing them into very fine specks, small enough particles to enter people’s lungs, as they were sucked up into the warm updraft of air forming the storm cells, before they returned to earth in the storm's cool down-draft, spreading across the land in the storm's efflux area.[23] Hospitals and medical centres in the city had to arduously manage 8,500 emergency calls in the space of just five hours, and the hospitalisation of 1400 people.[24]

See also[edit]

References[edit]

  1. ^ "SOUTHERLY BUSTER". Wellington Times. NSW: National Library of Australia. 23 December 1901. p. 2. Retrieved 27 March 2015.
  2. ^ Southerly Busters Explained. The Australian Government Bureau of Meteorology. Accessed 21 February 2012.
  3. ^ Naranjo, Ralph (1994-12-01), "Forecasts and false steps. (includes related information on June 1994 Pacific storm)(Safety at Sea)", Cruising World, Bonnier Corporation, 20 (12): 42, ISSN 0098-3519
  4. ^ Cassiily, M. 1945. The frontology of sub-tropical Australia. RAAF Met. Services Weather Development and Res. Bulletin. 1. 5-28.
  5. ^ 1850, B. C. Peck, Recollections of Sydney, quoted in 1978, G. A. Wilkes, A Dictionary of Australian Colloquialisms, ISBN 0-424-00034-2
  6. ^ a b Arthur Phillip Chapter of Fellowship of First Fleeters - WEATHER SECRETS OF THE FIRST FLEET VOYAGE
  7. ^ Helen J. Reid and Lance M. Leslie School of Mathematics, University of New South Wales, Sydney, Australia
  8. ^ 1995, Journal of Meteorology, Volume 20, Issues 200-204, page 213
  9. ^ ""Southerly Buster" Relieves City". The Sydney Morning Herald. National Library of Australia. 17 December 1953. p. 1. Retrieved 27 March 2015.
  10. ^ a b c The Big Bust - Southerly Busters Explained! - The Bureau of Meteorology
  11. ^ 1997, Peter Baines, Kathy McInnes, 24. The southerly buster, Eric Kenneth Webb (editor), Windows on Meteorology: Australian Perspective,
  12. ^ Berson, F.A., bid, D.G. and Troup, A.J. 1957. The summer cool change at southeastern Australia. I. General behaviour. Tech. Pap. No. 8. CSIRO Div. of Met. Phys.
  13. ^ Climate Change in the Sydney Metropolitan Catchments
  14. ^ THE DYNAMICS OF THE SOUTHERLY BUSTER P.G. Baines CSIRO Division of Atmospheric physics, Aspendale, June 1980
  15. ^ Berson, F.A., bid, D.G. and Troup, A.J. 1957. The summer cool change at southeastern Australia. I. General behaviour. Tech. Pap. No. 8. CSIRO Div. of Met. Phys.
  16. ^ Victoria. Ports and Harbors Division (1970), Sailing directions : Victoria including Bass Strait, Government Printer, retrieved 27 March 2015 – page 25 lines 15 – 29... regarding the prevalence of the Southerly Buster in a widespread area of south-east Australia, and not confined to Sydney.
  17. ^ Melbourne weather: Quick change sees temperature slip from sticky to chilly by Emily Woods, Ebony Bowden. 27 March 2017. The Age
  18. ^ Melbourne weather: How winds from the north and west create 'change days' by Belinda Smith, Tuesday November 13, 2018
  19. ^ meteorological reports. 1949. Aviation meteorology of south America. Met. Office Reports, VoI.,1, 1-50.
  20. ^ Ebsart, L.F., Pagnotti, V. and Lettau, B. 19 . Climatological aspects of Eastern United States back-door cold frontal passages.Mon. Weath Rev., 101, 627-35,
  21. ^ Melbourne thunderstorm asthma victims left waiting for ambulances which had not been despatched by Karen Percy (ABC News)
  22. ^ Coronial investigation uncovers tenth thunderstorm asthma death by Aisha Dow (The Age)
  23. ^ Thunderstorm asthma deaths: ambulance dispatch 'unlikely' factor – coroner by Melissa Davey (The Guardian)
  24. ^ Inquest into deaths of 10 Victorians from thunderstorm asthma hears common theme by Rohan Smith (News.com.au)