roaring forties
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roaring forties
(′rör·iŋ ′för·dēz)
(meteorology) A popular nautical term for the stormy ocean regions between 40° and 50° latitude; it usually refers to the Southern Hemisphere, where there is an almost completely uninterrupted belt of ocean with strong prevailing westerly winds.
roaring forties, name applied, especially by sailors, to the latitudes between 40°S and 50°S, where the prevailing westerly winds are strong and steady. Unlike the winds in the Northern Hemisphere, those in the roaring forties are not impeded by large land areas.
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Roaring Forties
For the electric company, see Roaring 40s.
Not to be confused with Roaring Twenties.
The Roaring Forties is the name given to strong westerly winds found in the Southern Hemisphere, generally between the latitudes of 40 and 50 degrees.[1] Air displaced from the Equator towards the South Pole, which travels close to the surface between the latitudes of 30 and 60 degrees south, combines with the earth's rotation to cause west-to-east air currents. Because there is little land below the 40th parallel, greater wind speeds are able to build than in the same region of the Northern Hemisphere.
The Roaring Forties was a major aid to trade ships sailing from Europe to the East Indies or Australasia during the Age of Sail, and in modern usage is favoured by yachtsmen on round-the-world voyages and competitions. The location of the Roaring Forties is not consistent, and shifts north or south depending on the season. Similar but stronger conditions occur in more southerly latitudes, and are referred to as the Furious Fifties and Shrieking or Screaming Sixties.
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Mechanics
See also: Atmospheric circulation
Hot air rises at the Equator and is pushed towards the poles by cooler air travelling towards the Equator (an atmospheric circulation feature known as the Hadley Cell).[1] At about 30 degrees from the equator, the outward-travelling air sinks to lower altitudes, and continues toward the poles closer to the ground (the Ferrel Cell), then rises up again from about 60 degrees as the air joins the Polar vortex.[1] This travel in the 30 to 60 degree zone combines with the rotation of the earth to move the air currents from west to east, creating westerly winds.[1]
Unlike the northern hemisphere, the large tracts of open ocean below 40th parallel south (interrupted only by Tasmania, New Zealand, and the southern part of South America) mean that higher windspeeds—the Roaring Forties—can develop.[1] Similar but stronger wind conditions are prevalent closer to the South Pole; these are referred to as the "Furious Fifties" (50 to 60 degrees south), and the "Shrieking" or "Screaming Sixties" (below 60 degrees south).[2] The latitude ranges for the Roaring Forties and similar winds are not consistent, shifting towards the South Pole in the southern summer, and towards the Equator in the southern winter.[1]
Use for sailing
During the Age of Sail, ships travelling from Europe to the East Indies or Australasia would sail down the west coast of Africa and round the Cape of Good Hope to use the Roaring Forties to speed their passage across the Indian Ocean,[3] then on the return leg, continue eastwards across the Pacific Ocean and under Cape Horn before sailing up the east coast of the Americas to home. "To run the easting down" was the phrase used to describe the fast passages achieved in the Roaring Forties.[4]
Round-the-world sailors also take advantage of the Roaring Forties to speed travel times, in particular those involved in record attempts or races.[4]
See also
References
- ^ a b c d e f Catchpole, Heather (20 September 2007). "Roaring forties". In Depth. ABC Science. http://www.abc.net.au/science/articles/2007/09/20/2038604.htm. Retrieved 7 April 2011.
- ^ "Exploring the Southern Ocean". Eco-Photo Explorers. 21 December 2009. http://www.ecophotoexplorers.com/antarctica_southocean.asp. Retrieved 7 April 2011.
- ^ Dear, I. C. B. & Kemp, Peter, ed. (2007). "Roaring Forties". The Oxford Companion to Ships and the Sea. Oxford Reference Online, Oxford University Press. ISBN 0-19-860616-8. OCLC 60793921. http://www.oxfordreference.com/views/ENTRY.html?subview=Main&entry=t225.e2007. Retrieved 14 April 2011.
- ^ a b Dear, I. C. B. & Kemp, Peter, ed. (2007). "Run the easting down, to". The Oxford Companion to Ships and the Sea. Oxford Reference Online, Oxford University Press. ISBN 0-19-860616-8. OCLC 60793921. http://www.oxfordreference.com/views/ENTRY.html?subview=Main&entry=t225.e2049. Retrieved 14 April 2011.
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