Editing Horse latitudes (section)

==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>