Editing Jet stream (section)

==Low-level jets==
There are wind maxima at lower levels of the atmosphere that are also referred to as jets.

===Barrier jet===
A barrier jet in the low levels forms just upstream of mountain chains, with the mountains forcing the jet to be oriented parallel to the mountains. The mountain barrier increases the [[Wind#Wind force scale|strength]] of the low level wind by 45 percent.<ref>J. D. Doyle. [http://cat.inist.fr/?aModele=afficheN&cpsidt=2721180 The influence of mesoscale orography on a coastal jet and rainband.] {{Webarchive|url=https://web.archive.org/web/20120106231443/http://cat.inist.fr/?aModele=afficheN&cpsidt=2721180 |date=6 January 2012 }} Retrieved on 25 December 2008.</ref> In the North American [[Great Plains]] a southerly low-level jet helps fuel overnight thunderstorm activity during the warm season, normally in the form of [[mesoscale convective system]]s which form during the overnight hours.<ref>Matt Kumijan, Jeffry Evans, and Jared Guyer. [http://www.spc.noaa.gov/publications/evans/kumjian.pdf The Relationship of the Great Plains Low-Level Jet to Nocturnal MCS Development.] {{Webarchive|url=https://web.archive.org/web/20080530032314/http://www.spc.noaa.gov/publications/evans/kumjian.pdf |date=30 May 2008 }} Retrieved on 8 May 2008.</ref> A similar phenomenon develops across Australia, which pulls moisture poleward from the [[Coral Sea]] towards cut-off lows which form mainly across southwestern portions of the [[continent]].<ref>L. Qi, L.M. Leslie, and S.X. Zhao. [https://archive.today/20130105053537/http://www3.interscience.wiley.com/journal/68500464/abstract?CRETRY=1&SRETRY=0 Cut-off low pressure systems over southern Australia: climatology and case study.] Retrieved on 8 May 2008.</ref>

===Coastal jet===
Coastal low-level jets are related to a sharp contrast between high temperatures over land and lower temperatures over the sea and play an important role in coastal weather, giving rise to strong coast parallel winds.<ref name="cardoso">{{cite journal |last1=Cardoso |first1=Rita M. |last2=Soares |first2=Pedro M. M. |last3=Lima |first3=Daniela C. A. |last4=Semedo |first4=Alvaro |title=The impact of climate change on the Iberian low-level wind jet: EURO-CORDEX regional climate simulation |journal=Tellus A: Dynamic Meteorology and Oceanography |date=1 December 2016 |volume=68 |issue=1 |pages=29005 |doi=10.3402/tellusa.v68.29005 |bibcode=2016TellA..6829005C |doi-access=free }}</ref> Most coastal jets are associated with the oceanic high-pressure systems and thermal low over land and are mainly located along cold eastern boundary marine currents, in [[upwelling]] regions offshore California, Peru–Chile, Benguela, Portugal, Canary and West Australia, and offshore Yemen–Oman.<ref name="cardoso" />

===Valley exit jet===
A [[valley exit jet]] is a strong, down-valley, elevated air current that emerges above the intersection of the valley and its adjacent plain. These winds frequently reach speeds of up to {{cvt|20|m/s|km/h mph|||}} at heights of {{cvt|40|-|200|m||}} above the ground. Surface winds below the jet tend to be substantially weaker, even when they are strong enough to sway vegetation.

Valley exit jets are likely to be found in valley regions that exhibit [[wikt:Special:Search/diurnal|diurnal]] mountain wind systems, such as those of the dry mountain ranges of the US. Deep valleys that terminate abruptly at a plain are more impacted by these factors than are those that gradually become shallower as downvalley distance increases.<ref>Whiteman, C. David (2000). ''Mountain Meteorology'', p. 193. Oxford University Press, New York. {{ISBN|978-0-19-803044-7}}, pp. 191–193.</ref>

===Africa===
{{See also|African easterly jet|Climate of Africa}}
There are several important low-level jets in Africa. Numerous low-level jets form in the [[Sahara]], and are important for the raising of [[dust]] off the desert surface. This includes a low-level jet in [[Chad]], which is responsible for dust emission from the [[Bodélé Depression]],<ref>Washington, R., and Todd, M. C. (2005), Atmospheric controls on mineral dust emission from the Bodélé Depression, Chad: The role of the low level jet, Geophys. Res. Lett., 32, L17701, doi:10.1029/2005GL023597.</ref> the world's most important single source of dust emission. [[The Somali Jet]], which forms off the East African coast is an important component of the global [[Hadley cell|Hadley]] circulation,<ref>Heaviside, C. and Czaja, A. (2013), Deconstructing the Hadley cell heat transport. Q.J.R. Meteorol. Soc., 139: 2181-2189. https://doi.org/10.1002/qj.2085</ref> and supplies water vapour to the [[Monsoon of South Asia|Asian Monsoon]].<ref>Boos, W.R. and Emanuel, K.A. (2009), Annual intensification of the Somali jet in a quasi-equilibrium framework: Observational composites. Q.J.R. Meteorol. Soc., 135: 319-335. https://doi.org/10.1002/qj.388</ref> Easterly low-level jets forming in valleys within the [[East African Rift|East African Rift System]] help account for the low rainfall in [[East Africa]] and support high rainfall in the [[Congo Basin]] rainforest.<ref>Munday, C., Savage, N., Jones, R.G. et al. Valley formation aridifies East Africa and elevates Congo Basin rainfall. Nature 615, 276–279 (2023). https://doi.org/10.1038/s41586-022-05662-5</ref> The formation of the [[thermal low]] over northern Africa leads to a low-level westerly jet stream from June into October, which provides the moist inflow to the West African [[monsoon]].<ref>B. Pu and K. H. Cook (2008). [http://adsabs.harvard.edu/abs/2008AGUFM.A13A0229P Dynamics of the Low-Level Westerly Jet Over West Africa.] {{Webarchive|url=https://web.archive.org/web/20171119014622/http://adsabs.harvard.edu/abs/2008AGUFM.A13A0229P |date=19 November 2017 }} American Geophysical Union, Fall Meeting 2008, abstract #A13A-0229. Retrieved on 8 March 2009.</ref>

While not technically a low-level jet, the mid-level [[African easterly jet]] (at 3000–4000 m above the surface) is also an important climate feature in Africa. It occurs during the northern hemisphere summer between 10°N and 20°N above in the [[Sahel]] region of West Africa.<ref>Dr. Alex DeCaria. [http://snowball.millersville.edu/~adecaria/ESCI344/esci344_lesson04_seasonal_mean_wind_fields.pdf Lesson 4 – Seasonal-mean Wind Fields.] {{Webarchive|url=https://web.archive.org/web/20130909054657/http://snowball.millersville.edu/~adecaria/ESCI344/esci344_lesson04_seasonal_mean_wind_fields.pdf |date=9 September 2013 }} Retrieved on 3 May 2008.</ref> It is considered to play a crucial role in the West African [[monsoon]],<ref>Kerry H. Cook. [http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2F1520-0442(1999)012%3C1165%3AGOTAEJ%3E2.0.CO%3B2 Generation of the African Easterly Jet and Its Role in Determining West African Precipitation.] {{Webarchive|url=https://web.archive.org/web/20200226084709/https://journals.ametsoc.org/doi/full/10.1175/1520-0442%281999%29012%3C1165%3AGOTAEJ%3E2.0.CO%3B2 |date=26 February 2020 }} Retrieved on 8 May 2008.</ref> and helps form the [[tropical wave]]s which move across the tropical Atlantic and eastern Pacific oceans during the warm season.<ref>[[Chris Landsea]]. AOML Frequently Asked Questions. [http://www.aoml.noaa.gov/hrd/tcfaq/A4.html Subject: A4) What is an easterly wave ?] {{webarchive|url=https://web.archive.org/web/20060718105909/http://www.aoml.noaa.gov/hrd/tcfaq/A4.html|date=18 July 2006}} Retrieved on 8 May 2008.</ref>