Editing Jet stream (section)

==Description==
[[File:Jetstreamconfig.jpg|thumb|right|250 px|General configuration of the polar and subtropical jet streams]]
[[File:Jetcrosssection.svg|lang=en|thumb|right|500 px|Cross section of the subtropical and polar jet streams by latitude]]

The polar and subtropical jet streams are the product of two factors: the atmospheric heating by [[solar radiation]] that produces the large-scale [[atmospheric circulation|polar, Ferrel, and Hadley]] circulation cells, and the action of the [[Coriolis force]] acting on those moving masses. The Coriolis force is caused by the planet's [[Planet#Rotation|rotation]] on its axis. The polar jet stream forms near the interface of the polar and Ferrel circulation cells; the subtropical jet forms near the boundary of the Ferrel and Hadley circulation cells.<ref>{{cite web | author=University of Illinois | url=http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cyc/upa/jet.rxml | title=Jet Stream | access-date=4 May 2008 | author-link=University of Illinois | archive-date=6 November 2018 | archive-url=https://web.archive.org/web/20181106095747/http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cyc/upa/jet.rxml | url-status=live }}</ref>

Polar jet streams are typically located near the 250 [[Pascal (unit)|hPa]] (about 1/4 atmosphere) pressure level, or {{cvt|30000|ft|mi km}} ( according to engineeringtoolbox's equation, 250 hPa is 33,700ft, not 30,000 ft ) above [[sea level]] while the weaker subtropical jet streams are somewhat higher.<ref>{{cite web |title=Jet Stream |url=https://skybrary.aero/articles/jet-stream |publisher=SKYbrary Aviation Safety |access-date=2 December 2024}}</ref><ref name="rmets" />

The polar jets, at lower altitude, and often intruding into mid-latitudes, strongly affect weather and aviation.<ref name="COOK">David R. Cook [http://www.newton.dep.anl.gov/askasci/wea00/wea00067.htm Jet Stream Behavior.] {{Webarchive|url=https://web.archive.org/web/20130602041056/http://www.newton.dep.anl.gov/askasci/wea00/wea00067.htm |date=2 June 2013 }} Retrieved on 8 May 2008.</ref><ref>B. Geerts and E. Linacre. [http://www-das.uwyo.edu/~geerts/cwx/notes/chap01/tropo.html The Height of the Tropopause.] {{Webarchive|url=https://web.archive.org/web/20200427090700/http://www-das.uwyo.edu/~geerts/cwx/notes/chap01/tropo.html |date=27 April 2020 }} Retrieved on 8 May 2008.</ref> The polar jet stream is most commonly found between latitudes 30° and 60° (closer to 60°), while the subtropical jet streams are located close to latitude 30°. These two jets merge at some locations and times, while at other times they are well separated. The northern polar jet stream is said to "follow the sun" as it slowly migrates northward as that hemisphere warms, and southward again as it cools.<ref>[[National Weather Service]] JetStream. [http://www.srh.noaa.gov/jetstream//global/jet.htm The Jet Stream.] {{Webarchive|url=https://web.archive.org/web/20131022193119/http://www.srh.noaa.gov/jetstream//global/jet.htm |date=22 October 2013 }} Retrieved on 8 May 2008.</ref><ref>McDougal Littell. [http://www.classzone.com/books/earth_science/terc/content/investigations/es1908/es1908page04.cfm Paths of Polar and Subtropical Jet Streams.] {{Webarchive|url=https://web.archive.org/web/20131113191900/http://www.classzone.com/books/earth_science/terc/content/investigations/es1908/es1908page04.cfm |date=13 November 2013 }} Retrieved on 13 May 2008.</ref>

The width of a jet stream is typically a few hundred kilometres or miles and its vertical thickness often less than {{convert|5|km|ft|abbr=off|spell=in}}.<ref>{{Cite web| url=https://www.pbs.org/wgbh/nova/balloon/science/jetstream.html| title=Frequently Asked Questions About The Jet Stream| website=[[PBS.org]]| publisher=[[Nova (American TV series)|NOVA]]| access-date=24 October 2008| archive-date=22 September 2008| archive-url=https://web.archive.org/web/20080922004117/http://www.pbs.org/wgbh/nova/balloon/science/jetstream.html| url-status=live}}</ref>

Jet streams are typically continuous over long distances, but discontinuities are also common.<ref name="GOMdef">Glossary of Meteorology. [http://amsglossary.allenpress.com/glossary/search?id=jet-stream1 Jet Stream.] {{webarchive|url=https://web.archive.org/web/20070301135911/http://amsglossary.allenpress.com/glossary/search?id=jet-stream1 |date=1 March 2007 }} Retrieved on 8 May 2008.</ref> The path of the jet typically has a meandering shape, and these meanders themselves propagate eastward, at lower speeds than that of the actual wind within the flow. Further, the meanders can split or form eddies.<ref>{{cite web |title=The Jet Stream |url=https://www.noaa.gov/jetstream/global/jet-stream |publisher=NOAA |date=20 September 2023 | access-date=2 December 2024}}</ref>

Each large meander, or wave, within the jet stream is known as a [[Rossby wave]] (planetary wave). Rossby waves are caused by changes in the [[Coriolis effect]] with latitude.<ref>{{cite book |last1=Rhines |first1=Peter |url=https://www.gfdl.noaa.gov/wp-content/uploads/files/user_files/io/rhines.pdf |title=Rossby Waves, in Encyclopedia of Atmospheric Sciences, Holton, Pyle and Curry Eds. |year=2002 |publisher=Academic Press, London |page=2780 pages |access-date=8 June 2022 |archive-date=7 October 2022 |archive-url=https://web.archive.org/web/20221007052127/https://www.gfdl.noaa.gov/wp-content/uploads/files/user_files/io/rhines.pdf |url-status=live }}</ref> [[Shortwave (meteorology)|Shortwave troughs]], are smaller scale waves superimposed on the Rossby waves, with a scale of {{convert|1000|to(-)|4000|km|mi|-2}} long,<ref>Glossary of Meteorology. [http://amsglossary.allenpress.com/glossary/search?id=cyclone-wave1 Cyclone wave.] {{webarchive|url=https://web.archive.org/web/20061026100253/http://amsglossary.allenpress.com/glossary/search?id=cyclone-wave1 |date=26 October 2006 }} Retrieved on 13 May 2008.</ref> that move along through the flow pattern around large scale, or longwave, "ridges" and "troughs" within Rossby waves.<ref>Glossary of Meteorology. [http://amsglossary.allenpress.com/glossary/search?p=1&query=short+wave&submit=Search Short wave.] {{webarchive|url=https://web.archive.org/web/20090609104745/http://amsglossary.allenpress.com/glossary/search?p=1&query=short+wave&submit=Search |date=9 June 2009 }} Retrieved on 13 May 2008.</ref>

The wind speeds are greatest where temperature [[Gradient|differences]] between air masses are greatest, and often exceed {{convert|92|km/h|kn mph|abbr=on}}.<ref name="GOMdef"/> Speeds of {{convert|400|km/h|kn mph|abbr=on}} have been measured.<ref name="ROBROY"/>

The jet stream moves from west to east bringing changes of weather.<ref>[http://www.space.com/scienceastronomy/solarsystem/jupiter_sidebar_000209.html Jet Streams On Earth and Jupiter.] {{webarchive|url=https://web.archive.org/web/20080724112429/http://www.space.com/scienceastronomy/solarsystem/jupiter_sidebar_000209.html |date=24 July 2008 }} Retrieved on 4 May 2008.</ref> The path of jet streams affects [[cyclonic]] storm systems at lower levels in the atmosphere, and so knowledge of their course has become an important part of weather forecasting. For example, in 2007 and 2012, Britain experienced severe flooding as a result of the polar jet staying south for the summer.<ref>{{Cite news |title = Why has it been so wet? |publisher = BBC |date = 23 July 2007 |url = http://news.bbc.co.uk/1/hi/magazine/6911918.stm |access-date = 31 July 2007 |archive-date = 26 September 2008 |archive-url = https://web.archive.org/web/20080926165122/http://news.bbc.co.uk/1/hi/magazine/6911918.stm |url-status = live }}</ref><ref>Blackburn, Mike; Hoskins, Brian; Slingo, Julia: {{Cite web |url = http://www.walker-institute.ac.uk/news/summer_2007.pdf |title = Notes on the Meteorological Context of the UK Flooding in June and July 2007 |publisher = Walker Institute for Climate System Research |date = 25 July 2007 |access-date = 29 August 2007 |url-status = dead |archive-url = https://web.archive.org/web/20070926220024/http://www.walker-institute.ac.uk/news/summer_2007.pdf |archive-date = 26 September 2007}}</ref><ref>{{Cite news |title = Why, oh why, does it keep raining? |publisher = BBC |date = 10 July 2012 |url = https://www.bbc.co.uk/news/science-environment-18783422 |access-date = 18 July 2012 |work = BBC News |last1 = Shukman |first1 = David |archive-date = 11 December 2012 |archive-url = https://web.archive.org/web/20121211152503/http://www.bbc.co.uk/news/science-environment-18783422 |url-status = live }}</ref>