Editing Horse latitudes

{{Use mdy dates|date=May 2023}}
{{Short description|Latitudes 30–35 degrees north and south of the Equator}}
{{About|the geographical area}}

[[File:Atmospheric circulation.svg|right|thumb|300px|A diagram showing the relative positions of the horse latitudes]]

The '''horse latitudes''' are the  [[latitude]]s about 30 degrees [[30th parallel north|north]] and [[30th parallel south|south]] of the [[Equator]].<ref>{{Cite web|last=US Department of Commerce|first=National Oceanic and Atmospheric Administration|title=What are the Horse Latitudes?|url=https://oceanservice.noaa.gov/facts/horse-latitudes.html|access-date=April 17, 2021|website=oceanservice.noaa.gov|language=EN-US}}</ref> They are characterized by sunny skies, calm winds, and very little precipitation. They are also known as [[Subtropics|subtropical]] ridges or highs. It is a [[high-pressure area]] at the divergence of  [[trade winds]] and the [[westerlies]].

==Etymology==
{{More citations needed|date=October 2024}}
A likely and documented explanation is that the term is derived from the "dead horse" ritual of seamen (see [[Flogging a dead horse#Earlier meaning|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. 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.<ref>Kemp, Peter. ''The Oxford Companion to Ships and the Sea'', London, Oxford University Press, 1976. pp. 233, 399</ref>

An alternative theory, of sufficient popularity to serve as an example of [[false etymology|folk etymology]], is that the term ''horse latitudes'' originates from when the [[Spanish Empire|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.<ref>''The Columbia Electronic Encyclopedia'', Sixth Edition. New York: Columbia University Press, 2003</ref>

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 [[ocean current|current]]. This was suggested by Edward Taube in his article "The Sense of 'Horse' in the Horse Latitudes".<ref>{{Cite web |url=http://www.worldwidewords.org/qa/qa-hor3.htm |title=World Wide Words |date=2008}}</ref> 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'' 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".<ref>{{Cite encyclopedia  |last=Horsburgh |first=James |title=India directory, or, Directions for sailing to and from the East Indies, China, Australia, Cape of Good Hope, Brazil, and the interjacent ports |year=1836 |entry=Fernando de Noronha |entry-url=https://archive.org/details/bub_gb_GuY2AQAAMAAJ/page/31/mode/1up |encyclopedia=India Directory, or, Directions for Sailing to and from the East Indies, China, Australia, Cape of Good Hope, Brazil and the Interjacent Ports... |url=https://archive.org/details/bub_gb_GuY2AQAAMAAJ/mode/1up |location=London |publisher=W. H. Allen |page=31}}</ref>

A further explanation is that this naming first appeared in the English translation of a German book {{Such as?|date=September 2024}} where ''Rossbreiten'' was incorrectly understood as ''Pferdbreiten''. The 'Ross latitudes' were named after the Englishman who described them first but could have been mistranslated, as ''Pferd'' and ''Ross'' are German synonyms for a horse. An incorrect translation could therefore have produced the term "horse latitudes".{{Citation needed|date=September 2024}}

==Formation==
The heating of the earth at the [[thermal equator]] leads to large amounts of convection along the [[Intertropical Convergence Zone]]. This air mass rises and then diverges, moving away from the equator in both northerly and southerly directions. As the air moves towards the mid-latitudes on both sides of the equator, it cools and sinks. This creates a 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, creating the [[Hadley cell]]<ref>Owen E. Thompson. "[http://www.atmos.umd.edu/~owen/CHPI/IMAGES/circs02.html Hadley Circulation Cell]". {{webarchive|url=https://web.archive.org/web/20090305122318/http://www.atmos.umd.edu/~owen/CHPI/IMAGES/circs02.html |date=March 5, 2009 }}.</ref> which during summer is reinforced by other climatological mechanisms such as the [[Rodwell–Hoskins mechanism]].<ref>{{cite journal |last1=Rodwell |first1=M. J. |last2=Hoskins |first2=B. J. |title=Subtropical Anticyclones and Summer Monsoons |journal=Journal of Climate |date=August 1, 2001 |volume=14 |issue=15 |pages=3192–3211 |doi=10.1175/1520-0442(2001)014<3192:SAASM>2.0.CO;2 |bibcode=2001JCli...14.3192R |bibcode-access=free |s2cid=58891085 |s2cid-access=free |language=EN |issn=0894-8755|doi-access=free }}</ref><ref>Channel Video Productions. Retrieved on February 11, 2007.</ref>  Many of the world's deserts are caused by these climatological [[high-pressure area]]s.

The subtropical ridge moves poleward during the summer, reaching its highest latitude in early autumn, before moving back during the cold season. The [[El Niño–Southern Oscillation]] (ENSO) can displace the northern hemisphere subtropical ridge, with [[La Niña]] 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 cyclone]]s 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 [[Tropic of Cancer|Cancer]]" and that in the Southern Hemisphere the "calms of [[Tropic of Capricorn|Capricorn]]".

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

==Migration==
[[File:Subtropicalridge2000091412.jpg|thumb|right|250px|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.<ref>{{cite book|url=https://archive.org/details/atmosphereweathe0000barr_l0e0|url-access=registration|quote=Atmosphere, weather, and climate.|title=Atmosphere, weather, and climate|author=Roger Graham Barry, Richard J. Chorley|page=[https://archive.org/details/atmosphereweathe0000barr_l0e0/page/117 117]|isbn=978-0-415-07760-6|year=1992|publisher=Routledge|access-date=November 9, 2009}}</ref>  The latitudinal movement of the subtropical ridge is strongly correlated with the progression of the monsoon trough or [[Intertropical Convergence Zone]].

Most [[tropical cyclone]]s 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.<ref>{{cite web |url-status=dead |work=Joint Typhoon Warning Center |date=2006 |url=http://www.nrlmry.navy.mil/forecaster_handbooks/Philippines2/Forecasters%20Handbook%20for%20the%20Philippine%20Islands%20and%20Surrounding%20Waters%20Typhoon%20Forecasting.3.pdf |title=3.3 JTWC Forecasting Philosophies |archive-url=https://web.archive.org/web/20120705161830/http://www.nrlmry.navy.mil/forecaster_handbooks/Philippines2/Forecasters%20Handbook%20for%20the%20Philippine%20Islands%20and%20Surrounding%20Waters%20Typhoon%20Forecasting.3.pdf |archive-date=July 5, 2012 |publisher=United States Navy |access-date=February 11, 2007 }}</ref>  When the subtropical ridge shifts due to ENSO, so will the preferred tropical cyclone tracks.  Areas west of Japan and Korea tend to experience far 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{{clarify|what is this break?|date=January 2024}} in the subtropical ridge tends to lie near [[130th meridian east|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.<ref>{{cite journal |first1=M. C. |last1=Wu |first2=W. L. |last2=Chang |first3=W. M. |last3=Leung |date=March 2004 |title=Impacts of El Nino-Southern Oscillation Events on Tropical Cyclone Landfalling Activity in the Western North Pacific |journal=Journal of Climate |pages=1419–1428 |volume=17 |issue=6 |doi=10.1175/1520-0442(2004)017<1419:IOENOE>2.0.CO;2 |doi-access=free |bibcode=2004JCli...17.1419W }}</ref>  In the Atlantic basin, the subtropical ridge position tends to lie about 5&nbsp;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 cyclogenesis|tropical cyclone development]] (1995–present), it amplifies the subtropical ridge across the central and eastern Atlantic.<ref>{{cite web |url-status=dead |first1=Gerald |last1=Bell |first2=Muthuvel |last2=Chelliah |first3=Kingste |last3=Mo |first4=Stanley |last4=Goldenberg |first5=Christopher |last5=Landsea |author-link5=Christopher Landsea |first6=Eric |last6=Blake |first7=Richard |last7=Pasch |date=17 May 2004 |url=http://www.cpc.noaa.gov/products/outlooks/hurricane2004/May/hurricane.html |title=NOAA: 2004 Atlantic Hurricane Outlook |archive-url=https://web.archive.org/web/20190101193913/http://www.cpc.noaa.gov/products/outlooks/hurricane2004/May/hurricane.html |archive-date=January 1, 2019 |website=[[Climate Prediction Center]] |access-date=February 11, 2007}}</ref>

==Role in weather formation and air quality==
{{See also|Air pollution}}
{{Main|Monsoon}}

[[File:Subtropridgejulyna.gif|thumb|right|250px|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.<ref>C.-P. Chang, Yongsheng Zhang, and Tim Li (1999). [https://archive.today/20130102002649/http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175/1520-0442(2000)013%3C4310:IAIVOT%3E2.0.CO;2 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 February 11, 2007.</ref> The subtropical ridge position is linked to how far northward monsoon moisture and [[thunderstorm]]s 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.<ref>Arizona State University (2009). [http://geography.asu.edu/aztc/monsoon.html Basics of the Arizona Monsoon & Desert Meteorology.] {{webarchive|url=https://web.archive.org/web/20090531091848/http://geography.asu.edu/aztc/monsoon.html |date=May 31, 2009 }} Retrieved on February 11, 2007.</ref>  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 hot, dry continental airmass returns from the northwest, and therefore the atmosphere dries out across the Desert Southwest, causing a break in the monsoon regime.<ref>David K. Adams (2009). [http://geochange.er.usgs.gov/sw/changes/natural/monsoon/ Review of Variability in the North American Monsoon.] [[United States Geological Survey]]. Retrieved on February 11, 2007.</ref>

In summer, On the subtropical ridge's western edge (generally on the eastern coast of continents), the high-pressure cell pushes poleward a southerly flow (northerly in the southern hemisphere) of tropical air. In the United States, the subtropical ridge [[Bermuda High]] helps create the hot, sultry summers with daily thunderstorms with buoyant airmasses typical of the [[Gulf of Mexico]] and the [[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 [[Pampas]], southern Queensland and, [[KwaZulu-Natal]] province in South Africa.<ref>Adelson, Glen; ''Environment: An Interdisciplinary Anthology'', pp. 466–467 {{ISBN|0300110774}}</ref>

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]].<ref>Myanmar government (2007). [http://www.kjc.gov.my/english/education/weather/haze01.html Haze.] {{webarchive|url=https://web.archive.org/web/20080224035453/http://www.kjc.gov.my/english/education/weather/haze01.html |date=February 24, 2008 }} Retrieved on February 11, 2007.</ref>  If the low-level [[relative humidity]] rises towards 100 percent overnight, [[fog]] can form.<ref>Robert Tardif (2002). [http://www.rap.ucar.edu/staff/tardif/Documents/CUprojects/ATOC5600/fog_characteristics.htm Fog characteristics.] {{webarchive|url=https://web.archive.org/web/20110520021633/http://www.rap.ucar.edu/staff/tardif/Documents/CUprojects/ATOC5600/fog_characteristics.htm |date=May 20, 2011 }} [[University Corporation for Atmospheric Research]]. Retrieved on February 11, 2007.</ref>

==See also==
* [[Atmospheric circulation]]
* [[Circle of latitude]]
* [[Doldrums]]
* [[Intertropical Convergence Zone]]
* [[Polar front]]
* [[Roaring Forties]]
* [[Sataspes]]

==References==
{{reflist}}

==Further reading==
* [http://www.infoplease.com/encyclopedia/weather/horse-latitudes.html Horse latitudes entry] in ''The Columbia Electronic Encyclopedia'', Sixth Edition. New York: Columbia University Press, 2003.
* {{Cite EB1911|wstitle=Horse Latitudes|short=x}}

== External links ==
{{Wiktionary|horse latitudes}}
* [http://www.us.oup.com/us/companion.websites/0195160223/studentresources/ch10/?view=usa Physical Geography – The Global Environment]
* [http://www.wiley.com/college/strahler/sc/strach5.html Winds and the Global Circulation System]

{{Cyclones}}

[[Category:Circles of latitude]]
[[Category:Age of Sail]]
[[Category:Meteorological phenomena]]
[[Category:Climate zones]]
[[Category:Anticyclones]]
[[Category:Tropical cyclone meteorology]]