Horse latitudes

Horse latitudes, subtropical ridges or subtropical highs are the subtropical latitudes between 30 and 35 degrees both north and south where Earth's atmosphere is dominated by the subtropical high, an area of high pressure, which suppresses precipitation and cloud formation, and has variable winds mixed with calm winds.

It is the product of the global air circulation cell known as the Hadley Cell. The subtropical ridge is characterized by mostly calm winds, which act to reduce air quality under its axis by causing fog overnight, and haze during daylight hours as a result of the stable atmosphere found near its location. The air descending from the upper troposphere flows out from its center at surface level toward the upper and lower latitudes of each hemisphere, creating both the trade winds and the westerlies. The subtropical ridge moves poleward during the summer, reaching its most northern latitude in early fall, before moving equatorward during the cold season. The El Niño southern climate oscillation (ENSO) can displace the northern hemisphere subtropical ridge, with La Niñas allowing for a more northerly axis for the ridge, while El Niños show flatter, more southerly ridges. The change of the ridge position during ENSO cycles changes the tracks of tropical cyclones that form around their equatorward and western peripheries. As the subtropical ridge varies in position and strength, it can enhance or depress monsoon regimes around their low-latitude periphery.

The horse latitudes are associated with the subtropical anticyclone. The belt in the Northern Hemisphere is sometimes called the "calms of Cancer" and that in the Southern Hemisphere the "calms of Capricorn".

The consistently warm, dry, and sunny conditions of the horse latitudes are the main cause for the existence of the world's major non-polar deserts, such as the Sahara Desert in Africa, the Arabian and Syrian deserts in the Middle East, the Mojave and Sonoran deserts in the southwestern United States and northern Mexico, all in the Northern Hemisphere; and the Atacama Desert, the Kalahari Desert, and the Australian Desert in the Southern Hemisphere.

Atmospheric circulation
A diagram showing the relative positions of the Horse latitudes


A likely and documented explanation is that the term is derived from the "dead horse" ritual of seamen (see Beating a dead horse). In this practice, the seaman paraded a straw-stuffed effigy of a horse around the deck before throwing it overboard. Seamen were paid partly in advance before a long voyage, and they frequently spent their pay all at once, resulting in a period of time without income. If they got advances from the ship's paymaster, they would incur debt. This period was called the "dead horse" time, and it usually lasted a month or two. The seaman's ceremony was to celebrate having worked off the "dead horse" debt. As west-bound shipping from Europe usually reached the subtropics at about the time the "dead horse" was worked off, the latitude became associated with the ceremony.[1]

An alternative theory, of sufficient popularity to serve as an example of folk etymology, is that the term horse latitudes originates from when the Spanish transported horses by ship to their colonies in the West Indies and Americas. Ships often became becalmed in mid-ocean in this latitude, thus severely prolonging the voyage; the resulting water shortages made it impossible for the crew to keep the horses alive, and they would throw the dead or dying animals overboard.[2]

A third explanation, which simultaneously explains both the northern and southern horse latitudes and does not depend on the length of the voyage or the port of departure, is based on maritime terminology: a ship was said to be 'horsed' when, although there was insufficient wind for sail, the vessel could make good progress by latching on to a strong current. This was suggested by Edward Taube in his article "The Sense of "Horse" in the Horse Latitudes" (Journal of Geography, October 1967).[3] He argued the maritime use of 'horsed' described a ship that was being carried along by an ocean current or tide in the manner of a rider on horseback. The term had been in use since the end of the seventeenth century. Furthermore, The India Directory [4] in its entry for Fernando de Noronha, an island off the coast of Brazil, mentions it had been visited frequently by ships "occasioned by the currents having horsed them to the westward".


Heating of the earth near the equator leads to large amounts of convection along the monsoon trough or Intertropical convergence zone. This air mass rises to the lower stratosphere where it diverges, moving away from the equator in the upper troposphere in both northerly and southerly directions. As it moves towards the mid-latitudes on both sides of the equator, the air cools and sinks. The resulting air mass subsidence creates a subtropical ridge of high pressure near the 30th parallel in both hemispheres. At the surface level, the sinking air diverges again with some returning to the equator, completing the Hadley circulation. This circulation on each side of the equator is known as the Hadley cell and leads to the formation of the subtropical ridge.[5] Many of the world's deserts are caused by these climatological high-pressure areas.


The subtropical ridge shows up as a large area of black (dryness) on this water vapor satellite image from September 2000.

The subtropical ridge starts migrating poleward in late spring reaching its zenith in early autumn before retreating equatorward during the late fall, winter, and early spring. The equatorward migration of the subtropical ridge during the cold season is due to increasing north-south temperature differences between the poles and tropics.[6] The latitudinal movement of the subtropical ridge is strongly correlated with the progression of the monsoon trough or Intertropical Convergence Zone.

Most tropical cyclones form on the side of the subtropical ridge closer to the equator, then move poleward past the ridge axis before recurving into the main belt of the Westerlies.[7] When the subtropical ridge shifts due to ENSO, so will the preferred tropical cyclone tracks. Areas west of Japan and Korea tend to experience many fewer September–November tropical cyclone impacts during El Niño and neutral years, while mainland China experiences much greater landfall frequency during La Niña years. During El Niño years, the break in the subtropical ridge tends to lie near 130°E, which would favor the Japanese archipelago, while in La Niña years the formation of tropical cyclones, along with the subtropical ridge position, shift west, which increases the threat to China.[8] In the Atlantic basin, the subtropical ridge position tends to lie about 5 degrees farther south during El Niño years, which leads to a more southerly recurvature for tropical cyclones during those years.

When the Atlantic Multidecadal Oscillation's mode is favorable to tropical cyclone development (1995–present), it amplifies the subtropical ridge across the central and eastern Atlantic.[9]

Role in weather formation and air quality

Mean July subtropical ridge position.

When the subtropical ridge in the northwest Pacific is stronger than normal, it leads to a wet monsoon season for Asia.[10] The subtropical ridge position is linked to how far northward monsoon moisture and thunderstorms extend into the United States. The subtropical ridge across North America typically migrates far enough northward to begin monsoon conditions across the Desert Southwest from July to September.[11] When the subtropical ridge is farther north than normal towards the Four Corners, monsoon thunderstorms can spread northward into Arizona. When the high pressure moves south, its circulation cuts off the moisture and the atmosphere dries out across the Desert Southwest, causing a break in the monsoon regime.[12]

On the subtropical ridges western edge (eastern coast of continents), the high pressure cell creates a southerly flow of tropical air toward the lower east sides of continents in the summer months. In the United States the subtropical ridge Bermuda High helps create the hot, sultry summers with daily thunderstorms typical of the Gulf of Mexico and East Coast of the United States. This flow pattern also occurs on the eastern coasts of continents in other subtropical climates such as South China, southern Japan, central-eastern South America, southern Queensland and KwaZulu Natal province in South Africa.[13]

When surface winds become light, the subsidence produced directly under the subtropical ridge can lead to a buildup of particulates in urban areas under the ridge, leading to widespread haze.[14] If the low level relative humidity rises towards 100 percent overnight, fog can form.[15]

See also


  1. ^ Kemp, Peter. The Oxford Companion to Ships and the Sea, London, Oxford University Press, 1976. pp. 233, 399
  2. ^ The Columbia Electronic Encyclopedia, Sixth Edition. New York: Columbia University Press, 2003
  3. ^ "World Wide Words". 2008.
  4. ^ Horsburgh, James (1836). India Directory, or, Directions For Sailing To And From The East Indies, China, Australia, Cape of Good Hope, Brazil and the Interjacent Ports... London: W. H. Allen.
  5. ^ Dr. Owen E. Thompson (1996). Hadley Circulation Cell. Archived 2009-03-05 at the Wayback Machine Channel Video Productions. Retrieved on 2007-02-11.
  6. ^ Roger Graham Barry, Richard J. Chorley (1992). Atmosphere, weather, and climate. Routledge. p. 117. ISBN 978-0-415-07760-6. Retrieved 2009-11-09.
  7. ^ Joint Typhoon Warning Center (2006). 3.3 JTWC Forecasting Philosophies. United States Navy. Retrieved on 2007-02-11.
  8. ^ M. C. Wu, W. L. Chang, and W. M. Leung (2003). Impacts of El Nino-Southern Oscillation Events on Tropical Cyclone Landfalling Activity in the Western North Pacific. Journal of Climate: pp. 1419–1428. Retrieved on 2007-02-11.
  9. ^ Dr. Gerald Bell, Dr. Muthuvel Chelliah, Dr. Kingste Mo, Stanley Goldenberg, Dr. Christopher Landsea, Eric Blake, Dr. Richard Pasch (2004). NOAA: 2004 Atlantic Hurricane Outlook. Climate Prediction Center. Retrieved on 2007-02-11.
  10. ^ C.-P. Chang, Yongsheng Zhang, and Tim Li (1999). Interannual and Interdecadal Variations of the East Asian Summer Monsoon and Tropical Pacific SSTs. Part I: Roles of the Subtropical Ridge. Journal of Climate: pp. 4310–4325. Retrieved on 2007-02-11.
  11. ^ Arizona State University (2009). Basics of the Arizona Monsoon & Desert Meteorology. Archived 2009-05-31 at the Wayback Machine Retrieved on 2007-02-11.
  12. ^ David K. Adams (2009). Review of Variability in the North American Monsoon. United States Geological Survey. Retrieved on 2007-02-11.
  13. ^ Adelson, Glen; Environment: An Interdisciplinary Anthology, pp. 466-467 ISBN 0300110774
  14. ^ Myanmar government (2007). Haze. Archived 2008-02-24 at the Wayback Machine Retrieved on 2007-02-11.
  15. ^ Robert Tardif (2002). Fog characteristics. Archived 2011-05-20 at the Wayback Machine University Corporation for Atmospheric Research. Retrieved on 2007-02-11.

Further reading

External links

30th parallel north

The 30th parallel north is a circle of latitude that is 30 degrees north of the Earth's equatorial plane. It stands one-third of the way between the equator and the North Pole and crosses Africa, Asia, the Pacific Ocean, North America and the Atlantic Ocean.

It is the approximate southern border of the horse latitudes in the Northern Hemisphere, meaning that much of the land area touching the 30th parallel is arid or semi-arid. If there is a source of wind from a body of water the area would more likely be subtropical.

At this latitude the sun is visible for 14 hours, 5 minutes during the summer solstice and 10 hours, 13 minutes during the winter solstice. On 21 June, the maximum altitude of the sun is 83.83 degrees and 36.17 degrees on 21 December.At this latitude:

One degree of longitude = 96.49 km or 59.95 mi

One minute of longitude = 1.61 km or 1.00 mi

One second of longitude = 26.80 m or 87.93 ft

33rd parallel north

The 33rd parallel north is a circle of latitude that is 33 degrees north of the Earth's equatorial plane. It crosses North Africa, Asia, the Pacific Ocean, North America and the Atlantic Ocean.

In Iraq, the parallel defined the limit of the southern no-fly zone from 4 September 1996 to 30 August 2003. (Before this time it had been set at the 32nd parallel north) as part of Operation Southern Watch.In the United States it approximately forms the border between Arkansas in the north and Louisiana on the south. (The border is actually a couple of kilometres north of the parallel.) The Louisiana Territory was that part of the 1803 Louisiana Purchase which lay north of the 33rd parallel.

The parallel is part of the horse latitudes.

At this latitude the sun is visible for 14 hours, 20 minutes during the summer solstice and 9 hours, 58 minutes during the winter solstice.

Azores High

The Azores High (Portuguese: Anticiclone dos Açores) also known as North Atlantic (Subtropical) High/Anticyclone or the Bermuda-Azores High, is a large subtropical semi-permanent centre of high atmospheric pressure typically found south of the Azores in the Atlantic Ocean, at the Horse latitudes. It forms one pole of the North Atlantic oscillation, the other being the Icelandic Low. The system influences the weather and climatic patterns of vast areas of North Africa and southern Europe, and to a lesser extent, eastern North America. The aridity of the Sahara Desert and the summer drought of the Mediterranean Basin is due to the large-scale subsidence and sinking motion of air in the system. In its summer position (the Bermuda High), the high is centered near Bermuda, and creates a southwest flow of warm tropical air toward the East Coast of the United States. In summer, the Azores-Bermuda High is strongest. The central pressure hovers around 1024 mbar (hPa).

This high-pressure block exhibits anticyclonic nature, circulating the air clockwise. Due to this direction of movement, African eastern waves are impelled along the southern periphery of the Azores High away from coastal West Africa towards the Caribbean, Central America, or the Bahamas, favouring tropical cyclogenesis, especially during the hurricane season.

Centers of action

Centers of action are extensive and almost stationary low-pressure areas or anticyclones which control the movement of atmospheric disturbances over a large area. This does not mean that the position of the center is constant over a specific area but that the monthly atmospheric pressure corresponds to a high or a low pressure.The French meteorologist Léon Teisserenc de Bort was the first in 1881 to apply this term to maxima and minima of pressure on daily charts. The main centers of action in the Northern Hemisphere are the Icelandic Low, the Aleutian Low, the Azores/Bermuda High, the Pacific High, the Siberian High (in winter), and the Asiatic Low (in summer). Sir Gilbert Walker used the same term to relate meteorological elements in a region to weather in the following season in other regions for the Southern Oscillation.

Gordon Pinsent

Gordon Edward Pinsent, CC, FRSC (born July 12, 1930) is a Canadian actor, screenwriter, director and playwright. He is known for his roles in numerous productions, including Away from Her, The Rowdyman, John and the Missus, A Gift to Last, Due South, The Red Green Show and Quentin Durgens, M.P. Since 1989, for nearly 30 years, he has served as the voice of Babar the elephant in television and film.

Horse Latitudes (album)

Horse Latitudes is an album by American singer/songwriter Jeffrey Foucault, released in 2011.

Horse Latitudes (poetry collection)

Horse Latitudes is tenth collection of poetry from the Northern Irish poet Paul Muldoon. It was published by Faber and Faber on 19 October 2006. It consists of 19 sonnets, each named for a battle beginning with the letter B.Its name stems from the areas north and south of the equator in which sailing ships tend to be becalmed, and where sailors traditionally (and possibly apocryphally) threw horses overboard, to lighten the ship and conserve food supplies (see Horse latitudes). The title was previously employed by Doors singer Jim Morrison for a song on the Strange Days album.

Like many of Muldoon's recent collections, Horse Latitudes contains a long poem – in this case a sonnet sequence ostensibly describing battle scenes through time and place. The collection also features several other characteristic features of Muldoon's work, such as fixed poetic forms and deft technique combined with a seemingly casual approach full of puns, slant-rhymes and wordplay. The collection is based on serious themes and emotions. Muldoon has reportedly said that the battle of Baghdad "is implied by omission", consistent with the themes of evasion, silence and censorship.This collection contains the poem "Sillyhow Stride", written in memory of Warren Zevon.

Horse Latitudes (song)

"Horse Latitudes" is the fifth song from The Doors second album, Strange Days. The song is a spoken word piece by Jim Morrison with the band providing incoherent noises as a backdrop. Morrison speaks the lyrics, telling of a ship at sea forced to jettison the onboard horses to lighten its load. The words are taken from one of the first poems Jim Morrison wrote, inspired by a book cover he saw at a local bookstore as a child.Keyboardist Ray Manzarek mentions in his book Light My Fire he never believed Morrison wrote "Horse Latitudes" at such a young age, claiming the words were "too mature".

This song often segued into "Moonlight Drive", or vice versa, which follows it on the album.

The lyric is a synthesis of Morrison's interests in maritime life thus the title Horse Latitudes and is also an obvious allusion to his naval upbringing.

It is also possible that Jim Morrison referred to the book the Toilers of the Sea by Victor Hugo, in which the practice of throwing horses into the sea in the 30-35 North degrees latitude is described.

Horse latitudes (disambiguation)

The horse latitudes are a geographical area north and south of the equator.

Horse Latitudes may also refer to:

The Horse Latitudes (album), an album by the band The Promise Ring

Horse Latitudes (book), a poetry collection by Paul Muldoon

"Horse Latitudes" (song), a song on the album Strange Days by The Doors

Horse Latitudes (album), a 2011 album by Jeffrey Foucault

Jeffrey Foucault

Jeffrey Foucault (born January 26, 1976) is an American songwriter and record producer from Whitewater, Wisconsin, United States, whose work marries the influence of American country, blues, rock 'n' roll, and folk music. He has released six full-length solo albums under his own name and two full-band lyrical collaborations with poet Lisa Olstein, under the moniker Cold Satellite. Foucault has toured extensively in the United States, Canada, the United Kingdom and Europe since 2001, in both full-band and solo appearances. Since 2013 he has performed as a duo with drummer Billy Conway (Morphine, Treat Her Right).

Foucault's solo releases were previously issued by western Massachusetts-based independent label Signature Sounds, including Stripping Cane (2004), Ghost Repeater (2006) and Horse Latitudes (2011). His 2015 release, Salt As Wolves, was self-released on BlueBlade Records. His bands have featured or included Eric Heywood (Son Volt, Pretenders, Ray Lamontagne), Bo Ramsey (Greg Brown, Lucinda Williams, Pieta Brown), Billy Conway (Morphine), Jennifer Condos (Joe Henry, Sam Phillips), Jeremy Moses Curtis (Booker T), David Goodrich (Chris Smither), Van Dyke Parks (Harry Nilsson, Ry Cooder, Ringo Starr) and Caitlin Canty.Foucault has produced three albums for other artists, including Hayward Williams's The Reef (2014), Caitlin Canty's Reckless Skyline (2015) and John Statz's Tulsa (2015).Don Henley performed Foucault's song, "Everybody's Famous", during his 2011 tour of California, and Foucault's songs have appeared on the television shows Sons of Anarchy, Preacher, and Nashville.

Foucault's 2015 release, Salt As Wolves, debuted at number 7 in the Billboard Top Blues Album Chart for the week of November 7, 2015.Foucault lives in New England with his wife, fellow songwriter Kris Delmhorst.

Live at the Hollywood Bowl (The Doors album)

Live at the Hollywood Bowl is the third official live album by the American rock band the Doors, released in May 1987 on Elektra Records. The concert was recorded on July 5, 1968, at the Hollywood Bowl in Los Angeles, the Doors' hometown. The 1987 LP release of this album is the Doors' shortest official release, at just 22 minutes and 19 seconds. A VHS video of the concert was also released, containing 14 songs.

The full version of the concert entitled Live at the Bowl '68 was released in October 2012 on CD, LP and Blu-ray Disc. A shortened version of the concert is on The Doors - 30 Years Commemorative Edition DVD.

Ritual Productions

Ritual Productions is a London-based independent record label launched in 2010.


Sataspes was a Persian navigator and cavalry commander whose name is derived from Sat (=100 sad) and Asp (= Horse, Asb). He is also credited with originating the term "horse latitudes".

Sataspes (who, according to Herodotus, was Xerxes I's cousin by his mother being Darius I's sister) had been condemned to death for kidnapping and raping Megabyzus's daughter. However his mother, Atossa, successfully convinced Xerxes to change the punishment to a more severe one - Sataspes was tasked to circumnavigate Africa. He took an Egyptian ship and crew, sailed through the Pillars of Hercules, and proceeded south for many months, but returned to Egypt without successfully completing his task. He claimed that at the farthest point he reached, he encountered a "dwarfish race, who wore a dress made from the palm tree", and that he was forced to return because his ship stopped and would not sail any further. Xerxes did not accept this excuse, and had him put to death. However, it has been suggested that Sataspes could have simply encountered the Benguela Current, which prevented him from sailing any farther.

Strange Days (album)

Strange Days is the second studio album by American rock band the Doors, released on September 25, 1967 by Elektra Records. The album was a commercial success, reaching number 3 on the US Billboard 200, and eventually earning RIAA platinum certification. The album contains the Top 30 hit singles "People Are Strange" and "Love Me Two Times".

Subsidence (atmosphere)

Subsidence, in the Earth's atmosphere, is most commonly caused by a low temperature. As the air cools, it becomes denser and moves towards the ground, as warm air becomes less dense and moves upwards (Atmospheric convection). Subsiding air is cold and dry and rises atmospheric pressure forming a high-pressure or anticyclonic area

Subsidence generally causes high barometric pressure as more air moves into the same space: the polar highs are areas of almost constant subsidence, as are the horse latitudes, and the areas of subsidence are the sources of much of the world's prevailing winds.

Subsidence also causes many smaller-scale weather phenomena, such as morning fog. An extreme form of subsidence is a downburst, which can result in damage similar to that produced by a tornado. A milder form of subsidence is referred to as downdraft.

The Doors – 30 Years Commemorative Edition

The Doors 30th Anniversary Collection is a music compilation DVD by the American rock band the Doors, released in 1999 and 2001. It compiles three films previously released by MCA/Universal Home Video: Live at the Hollywood Bowl (1987), Dance on Fire (1985) and The Soft Parade - A Retrospective (1991).

Live at the Hollywood Bowl (62 min) is a Doors' concert filmed live at the Hollywood Bowl in the summer of 1968.

Dance on Fire (65 mins) is a collection of promotional clips, live concert performances, TV appearances and rare behind-the-scenes film footage. It was directed by keyboardist Ray Manzarek and includes 14 songs one of which is a short film by Manzarek backed by the song "L.A. Woman".

The Soft Parade - A Retrospective (48 mins) includes previously unreleased band performances, interview footage and the Doors' last televised appearance on PBS in 1969 (in the aftermath of Jim Morrison's arrest arrest and later trial for indecent exposure).

In 2008 The Doors and MCA/Universal Home Video: release The DVD video under The name The Doors Collection – Collector's Edition.

The Horse Latitudes

The Horse Latitudes is an EP by the emo band The Promise Ring. It was released in 1997 on Jade Tree Records. The album was released between their debut album 30° Everywhere and their hit record Nothing Feels Good.

The Promise Ring

The Promise Ring is an American rock band from Milwaukee, Wisconsin that are recognized as part of the second wave of emo. Formed in 1995, they first split up in 2002 and have reunited occasionally since 2005. The band has released four full-length studio albums, plus various EPs and singles.


The westerlies, anti-trades, or prevailing westerlies, are prevailing winds from the west toward the east in the middle latitudes between 30 and 60 degrees latitude. They originate from the high-pressure areas in the horse latitudes and trend towards the poles and steer extratropical cyclones in this general manner. Tropical cyclones which cross the subtropical ridge axis into the westerlies recurve due to the increased westerly flow. The winds are predominantly from the southwest in the Northern Hemisphere and from the northwest in the Southern Hemisphere.

The westerlies are strongest in the winter hemisphere and times when the pressure is lower over the poles, while they are weakest in the summer hemisphere and when pressures are higher over the poles. The westerlies are particularly strong, especially in the Southern Hemisphere, in areas where land is absent, because land amplifies the flow pattern, making the current more north-south oriented, slowing the westerlies. The strongest westerly winds in the middle latitudes can come in the roaring forties, between 40 and 50 degrees latitude. The westerlies play an important role in carrying the warm, equatorial waters and winds to the western coasts of continents, especially in the southern hemisphere because of its vast oceanic expanse.

Circles of latitude / Meridians showing the Horse latitudes


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