# Horse latitudes

> Mediated Wiki article. Canonical URL: https://mediated.wiki/source/Horse_latitudes
> Markdown URL: https://mediated.wiki/source/Horse_latitudes.md
> Source: https://en.wikipedia.org/wiki/Horse_latitudes
> Source revision: 1347063674
> License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/)

Latitudes 30–35 degrees north and south of the Equator

This article is about the geographical area. For other uses, see [Horse latitudes (disambiguation)](/source/Horse_latitudes_(disambiguation)).

A diagram showing the relative positions of the horse latitudes

The **horse latitudes** are the [latitudes](/source/Latitude) about 30 degrees [north](/source/30th_parallel_north) and [south](/source/30th_parallel_south) of the [equator](/source/Equator).[1] They are characterized by sunny skies, calm winds, and very little precipitation. They are also known as [subtropical](/source/Subtropics) ridges or highs. It is a [high-pressure area](/source/High-pressure_area) at the divergence of [trade winds](/source/Trade_winds) and the [westerlies](/source/Westerlies).

## Etymology

This article needs more citations. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Find sources: "Horse latitudes" – news · newspapers · books · scholar · JSTOR (October 2024) (Learn how and when to remove this message)

A likely and documented explanation is that the term is derived from the "dead horse" ritual of seamen (see [Beating a dead horse](/source/Flogging_a_dead_horse#Earlier_meaning)). In this practice, the seaman paraded a straw-stuffed [effigy](/source/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.[2]

An alternative theory, of sufficient popularity to serve as an example of [folk etymology](/source/False_etymology), is that the term *horse latitudes* originates from when the [Spanish](/source/Spanish_Empire) 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.[3]

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](/source/Ocean_current). This was suggested by Edward Taube in his article "The Sense of 'Horse' in the Horse Latitudes".[4] 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 carriage pulled by a horse. The term had been in use since the end of the seventeenth century. Furthermore, *The India Directory* in its entry for [Fernando de Noronha](/source/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".[5]

A further explanation is that this naming first appeared in the English translation of a German book [*[example needed](https://en.wikipedia.org/wiki/Wikipedia:AUDIENCE)*] 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](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

## Formation

The heating of the earth at the [thermal equator](/source/Thermal_equator) leads to large amounts of convection along the [Intertropical Convergence Zone](/source/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](/source/Hadley_cell)[6] which during summer is reinforced by other climatological mechanisms such as the [Rodwell–Hoskins mechanism](/source/Rodwell%E2%80%93Hoskins_mechanism).[7][8] Many of the world's deserts are caused by these climatological [high-pressure areas](/source/High-pressure_area).

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](/source/El_Ni%C3%B1o%E2%80%93Southern_Oscillation) (ENSO) can displace the northern hemisphere subtropical ridge, with [La Niña](/source/La_Ni%C3%B1a) 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](/source/Tropical_cyclone) that form around their equatorward and western peripheries. As the subtropical ridge varies in position and strength, it can enhance or depress [monsoon](/source/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](/source/Tropic_of_Cancer)" and that in the Southern Hemisphere the "calms of [Capricorn](/source/Tropic_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 hot deserts, such as the [Sahara Desert](/source/Sahara_Desert) in Africa, the [Arabian](/source/Arabian_Desert) and [Syrian](/source/Syrian_Desert) deserts in the Middle East, the [Mojave](/source/Mojave_Desert) and [Sonoran](/source/Sonoran_Desert) deserts in the southwestern United States and northern Mexico, all in the Northern Hemisphere; and the [Atacama Desert](/source/Atacama_Desert), the [Namib Desert](/source/Namib), the [Kalahari Desert](/source/Kalahari_Desert), and the [Australian Desert](/source/Australian_Desert) in the Southern Hemisphere.

## Migration

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.[9] The latitudinal movement of the subtropical ridge is strongly correlated with the progression of the monsoon trough or [Intertropical Convergence Zone](/source/Intertropical_Convergence_Zone).

Most [tropical cyclones](/source/Tropical_cyclone) 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.[10] 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](/source/El_Ni%C3%B1o) and neutral years, while mainland China experiences much greater landfall frequency during [La Niña](/source/La_Ni%C3%B1a) years. During El Niño years, the break[*[clarification needed](https://en.wikipedia.org/wiki/Wikipedia:Please_clarify)*] in the subtropical ridge tends to lie near [130°E](/source/130th_meridian_east), 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.[11] 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](/source/Atlantic_multidecadal_oscillation)'s mode is favorable to [tropical cyclone development](/source/Tropical_cyclogenesis) (1995–present[*[when?](https://en.wikipedia.org/wiki/Wikipedia:Manual_of_Style/Dates_and_numbers#Chronological_items)*]), it amplifies the subtropical ridge across the central and eastern Atlantic.[12]

## Role in weather formation and air quality

See also: [Air pollution](/source/Air_pollution)

Main article: [Monsoon](/source/Monsoon)

Mean July subtropical ridge position

When the subtropical ridge in the northwest Pacific is stronger than normal, it leads to a wet [monsoon](/source/Monsoon) season for Asia.[13] The subtropical ridge position is linked to how far northward monsoon moisture and [thunderstorms](/source/Thunderstorm) 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.[14] When the subtropical ridge is farther north than normal towards the [Four Corners](/source/Four_Corners), monsoon thunderstorms can spread northward into [Arizona](/source/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.[15]

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](/source/Bermuda_High) helps create the hot, sultry summers with daily thunderstorms with buoyant airmasses typical of the [Gulf of Mexico](/source/Gulf_of_Mexico) and the [East Coast of the United States](/source/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](/source/Pampas), southern Queensland and, [KwaZulu-Natal](/source/KwaZulu-Natal) province in South Africa.[16]

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](/source/Haze).[17] If the low-level [relative humidity](/source/Relative_humidity) rises towards 100 percent overnight, [fog](/source/Fog) can form.[18]

## See also

- [Atmospheric circulation](/source/Atmospheric_circulation)

- [Circle of latitude](/source/Circle_of_latitude)

- [Doldrums](/source/Doldrums)

- [Intertropical Convergence Zone](/source/Intertropical_Convergence_Zone)

- [Polar front](/source/Polar_front)

- [Roaring Forties](/source/Roaring_Forties)

- [Sataspes](/source/Sataspes)

## References

1. **[^](#cite_ref-1)** US Department of Commerce, National Oceanic and Atmospheric Administration. ["What are the Horse Latitudes?"](https://oceanservice.noaa.gov/facts/horse-latitudes.html). *oceanservice.noaa.gov*. Retrieved April 17, 2021.

1. **[^](#cite_ref-2)** Kemp, Peter. *The Oxford Companion to Ships and the Sea*, London, Oxford University Press, 1976. pp. 233, 399

1. **[^](#cite_ref-3)** *The Columbia Electronic Encyclopedia*, Sixth Edition. New York: Columbia University Press, 2003

1. **[^](#cite_ref-4)** ["World Wide Words"](https://www.worldwidewords.org/qa/qa-hor3.htm). 2008.

1. **[^](#cite_ref-5)** Horsburgh, James (1836). ["Fernando de Noronha"](https://archive.org/details/bub_gb_GuY2AQAAMAAJ/page/31/mode/1up). [*India Directory, or, Directions for Sailing to and from the East Indies, China, Australia, Cape of Good Hope, Brazil and the Interjacent Ports...*](https://archive.org/details/bub_gb_GuY2AQAAMAAJ/mode/1up) London: W. H. Allen. p. 31.

1. **[^](#cite_ref-6)** Owen E. Thompson. "[Hadley Circulation Cell](http://www.atmos.umd.edu/~owen/CHPI/IMAGES/circs02.html)". [Archived](https://web.archive.org/web/20090305122318/http://www.atmos.umd.edu/~owen/CHPI/IMAGES/circs02.html) March 5, 2009, at the [Wayback Machine](/source/Wayback_Machine).

1. **[^](#cite_ref-7)** Rodwell, M. J.; Hoskins, B. J. (August 1, 2001). ["Subtropical Anticyclones and Summer Monsoons"](https://doi.org/10.1175%2F1520-0442%282001%29014%3C3192%3ASAASM%3E2.0.CO%3B2). *Journal of Climate*. **14** (15): 3192–3211. [Bibcode](/source/Bibcode_(identifier)):[2001JCli...14.3192R](https://ui.adsabs.harvard.edu/abs/2001JCli...14.3192R). [doi](/source/Doi_(identifier)):[10.1175/1520-0442(2001)014<3192:SAASM>2.0.CO;2](https://doi.org/10.1175%2F1520-0442%282001%29014%3C3192%3ASAASM%3E2.0.CO%3B2). [ISSN](/source/ISSN_(identifier)) [0894-8755](https://search.worldcat.org/issn/0894-8755). [S2CID](/source/S2CID_(identifier)) [58891085](https://api.semanticscholar.org/CorpusID:58891085).

1. **[^](#cite_ref-8)** Channel Video Productions. Retrieved on February 11, 2007.

1. **[^](#cite_ref-9)** Roger Graham Barry, Richard J. Chorley (1992). [*Atmosphere, weather, and climate*](https://archive.org/details/atmosphereweathe0000barr_l0e0). Routledge. p. [117](https://archive.org/details/atmosphereweathe0000barr_l0e0/page/117). [ISBN](/source/ISBN_(identifier)) [978-0-415-07760-6](https://en.wikipedia.org/wiki/Special:BookSources/978-0-415-07760-6). Retrieved November 9, 2009. Atmosphere, weather, and climate.

1. **[^](#cite_ref-10)** ["3.3 JTWC Forecasting Philosophies"](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) (PDF). *Joint Typhoon Warning Center*. United States Navy. 2006. Archived from [the original](http://www.nrlmry.navy.mil/forecaster_handbooks/Philippines2/Forecasters%20Handbook%20for%20the%20Philippine%20Islands%20and%20Surrounding%20Waters%20Typhoon%20Forecasting.3.pdf) (PDF) on July 5, 2012. Retrieved February 11, 2007.

1. **[^](#cite_ref-11)** Wu, M. C.; Chang, W. L.; Leung, W. M. (March 2004). ["Impacts of El Nino-Southern Oscillation Events on Tropical Cyclone Landfalling Activity in the Western North Pacific"](https://doi.org/10.1175%2F1520-0442%282004%29017%3C1419%3AIOENOE%3E2.0.CO%3B2). *Journal of Climate*. **17** (6): 1419–1428. [Bibcode](/source/Bibcode_(identifier)):[2004JCli...17.1419W](https://ui.adsabs.harvard.edu/abs/2004JCli...17.1419W). [doi](/source/Doi_(identifier)):[10.1175/1520-0442(2004)017<1419:IOENOE>2.0.CO;2](https://doi.org/10.1175%2F1520-0442%282004%29017%3C1419%3AIOENOE%3E2.0.CO%3B2).

1. **[^](#cite_ref-12)** Bell, Gerald; Chelliah, Muthuvel; Mo, Kingste; Goldenberg, Stanley; [Landsea, Christopher](/source/Christopher_Landsea); Blake, Eric; Pasch, Richard (May 17, 2004). ["NOAA: 2004 Atlantic Hurricane Outlook"](https://web.archive.org/web/20190101193913/http://www.cpc.noaa.gov/products/outlooks/hurricane2004/May/hurricane.html). *[Climate Prediction Center](/source/Climate_Prediction_Center)*. Archived from [the original](http://www.cpc.noaa.gov/products/outlooks/hurricane2004/May/hurricane.html) on January 1, 2019. Retrieved February 11, 2007.

1. **[^](#cite_ref-13)** 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.](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) Journal of Climate: pp. 4310–4325. Retrieved on February 11, 2007.

1. **[^](#cite_ref-14)** Arizona State University (2009). [Basics of the Arizona Monsoon & Desert Meteorology.](http://geography.asu.edu/aztc/monsoon.html) [Archived](https://web.archive.org/web/20090531091848/http://geography.asu.edu/aztc/monsoon.html) May 31, 2009, at the [Wayback Machine](/source/Wayback_Machine) Retrieved on February 11, 2007.

1. **[^](#cite_ref-15)** David K. Adams (2009). [Review of Variability in the North American Monsoon.](https://geochange.er.usgs.gov/sw/changes/natural/monsoon/) [United States Geological Survey](/source/United_States_Geological_Survey). Retrieved on February 11, 2007.

1. **[^](#cite_ref-16)** Adelson, Glen; *Environment: An Interdisciplinary Anthology*, pp. 466–467 [ISBN](/source/ISBN_(identifier)) [0300110774](https://en.wikipedia.org/wiki/Special:BookSources/0300110774)

1. **[^](#cite_ref-17)** Myanmar government (2007). [Haze.](http://www.kjc.gov.my/english/education/weather/haze01.html) [Archived](https://web.archive.org/web/20080224035453/http://www.kjc.gov.my/english/education/weather/haze01.html) February 24, 2008, at the [Wayback Machine](/source/Wayback_Machine) Retrieved on February 11, 2007.

1. **[^](#cite_ref-18)** Robert Tardif (2002). [Fog characteristics.](http://www.rap.ucar.edu/staff/tardif/Documents/CUprojects/ATOC5600/fog_characteristics.htm) [Archived](https://web.archive.org/web/20110520021633/http://www.rap.ucar.edu/staff/tardif/Documents/CUprojects/ATOC5600/fog_characteristics.htm) May 20, 2011, at the [Wayback Machine](/source/Wayback_Machine) [University Corporation for Atmospheric Research](/source/University_Corporation_for_Atmospheric_Research). Retrieved on February 11, 2007.

## Further reading

- [Horse latitudes entry](http://www.infoplease.com/encyclopedia/weather/horse-latitudes.html) in *The Columbia Electronic Encyclopedia*, Sixth Edition. New York: Columbia University Press, 2003.

- ["Horse Latitudes"](https://en.wikisource.org/wiki/1911_Encyclop%C3%A6dia_Britannica/Horse_Latitudes). *[Encyclopædia Britannica](/source/Encyclop%C3%A6dia_Britannica_Eleventh_Edition)* (11th ed.). 1911.

## External links

Look up ***[horse latitudes](https://en.wiktionary.org/wiki/horse_latitudes)*** in Wiktionary, the free dictionary.

- [Physical Geography – The Global Environment](http://www.us.oup.com/us/companion.websites/0195160223/studentresources/ch10/?view=usa)

- [Winds and the Global Circulation System](http://www.wiley.com/college/strahler/sc/strach5.html)

v t e Cyclones and anticyclones of the world (centers of action) Concepts Anticyclonic storm Storm High-pressure area Low-pressure area Rapid intensification Explosive cyclogenesis Central dense overcast Annular tropical cyclone Bar (tropical cyclone) Superstorm Hypercane Tropical cyclones and climate change Post-tropical cyclone Sting jet List Rainband Anticyclone Northern Hemisphere North Polar High Siberian High Azores High North American High North Pacific High Ridiculously Resilient Ridge Subtropical ridge Southern Hemisphere Bolivian High South Polar High South Atlantic High South Pacific High Kalahari High Australian High Subtropical ridge Cyclone Synoptic scale Surface-based Polar North Polar low South Polar low Great Arctic Cyclone of 2012 Extratropical North America Continental Lee Cyclone Alberta clipper Colorado low Great Basin low Bighorn Low Other Panhandle hook November gale Oceanic Aleutian Low Hatteras low Nor'easter Gulf low Pacific Northwest windstorm Europe Icelandic Low Genoa low European windstorm Asia Asiatic Low Western Disturbance Continental North Asian storms East Asian-northwest Pacific storms Southern Hemisphere Southern Ocean cyclone Sudestada Subtropical Kona storm Australian east coast low Black nor'easter Lake Huron cyclone Mediterranean tropical-like cyclone Thermal Tropical (Outline) Northern Hemisphere Atlantic hurricane Cape Verde hurricane Pacific hurricane Typhoon North Indian Ocean tropical cyclone Mediterranean tropical-like cyclone Black Sea tropical-like cyclone Southern Hemisphere South-West Indian Ocean tropical cyclone Australian region tropical cyclone South Pacific tropical cyclone South Atlantic tropical cyclone Upper level Cold-core low Cut-off low Polar vortex Upper tropospheric cyclonic vortex Mesoscale Mesoscale ocean eddies Catalina eddy Haida Eddies Mesoscale convective system Wake Low Mesohigh Mesoscale convective vortex Line echo wave pattern Whirlwind Major Mesocyclone Supercell Low-topped supercell Wall cloud Funnel cloud Tornado Multiple-vortex tornado Satellite tornado Anticyclonic tornado Landspout Waterspout Minor Gustnado Dust devil Steam devil Fire whirl Tropical cyclones portal Tornadoes portal

---
Adapted from the Wikipedia article [Horse latitudes](https://en.wikipedia.org/wiki/Horse_latitudes) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Horse_latitudes?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.