Editing Jet stream (section)

==Changes due to climate cycles==

===Effects of ENSO===
[[File:El nino north american weather.png|thumb|right|250 px|Impact of [[El Niño]] and [[La Niña]] on North America]]
{{Main|Effects of the El Niño–Southern Oscillation in the United States}}
[[El Niño–Southern Oscillation]] (ENSO) influences the average location of upper-level jet streams, and leads to cyclical variations in precipitation and temperature across North America, as well as affecting [[tropical cyclone]] development across the eastern Pacific and Atlantic basins. Combined with the [[Pacific Decadal Oscillation]], ENSO can also impact cold season rainfall in Europe.<ref>Davide Zanchettin, Stewart W. Franks, Pietro Traverso, and Mario Tomasino. [http://www3.interscience.wiley.com/journal/114802316/abstract On ENSO impacts on European wintertime rainfalls and their modulation by the NAO and the Pacific multi-decadal variability described through the PDO index.]{{dead link|date=February 2019|bot=medic}}{{cbignore|bot=medic}} Retrieved on 13 May 2008.</ref> Changes in ENSO also change the location of the jet stream over South America, which partially affects precipitation distribution over the continent.<ref name="Caio">Caio Augusto dos Santos Coelho and Térico Ambrizzi. [http://www.cptec.inpe.br/~caio/chile2000.pdf 5A.4. Climatological Studies of the Influences of El Niño Southern Oscillation Events in the Precipitation Pattern Over South America During Austral Summer.] {{Webarchive|url=https://web.archive.org/web/20080530032314/http://www.cptec.inpe.br/~caio/chile2000.pdf |date=30 May 2008 }} Retrieved on 13 May 2008.</ref>

====El Niño====
During [[El Niño]] events, increased precipitation is expected in California due to a more southerly, zonal, storm track.<ref>John Monteverdi and Jan Null. [http://tornado.sfsu.edu/geosciences/elnino/elnino.html "WESTERN REGION TECHNICAL ATTACHMENT NO. 97-37 November 21, 1997: El Niño and California Precipitation."] {{Webarchive|url=https://web.archive.org/web/20091227155828/http://tornado.sfsu.edu/geosciences/elnino/elnino.html |date=27 December 2009 }} Retrieved on 28 February 2008.</ref> During the Niño portion of ENSO, increased precipitation falls along the Gulf coast and Southeast due to a stronger than normal, and more southerly, polar jet stream.<ref>[[Climate Prediction Center]]. [http://www.cpc.noaa.gov/products/analysis_monitoring/ensocycle/ensorain.shtml El Niño (ENSO) Related Rainfall Patterns Over the Tropical Pacific.] {{Webarchive|url=https://web.archive.org/web/20100528035733/http://www.cpc.noaa.gov/products/analysis_monitoring/ensocycle/ensorain.shtml |date=28 May 2010 }} Retrieved on 28 February 2008.</ref> Snowfall is greater than average across the southern Rockies and Sierra Nevada mountain range, and is well below normal across the Upper Midwest and Great Lakes states.<ref name="cpc.ncep.noaa.gov">[[Climate Prediction Center]]. [http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/us_impacts/ustp_impacts.shtml ENSO Impacts on United States Winter Precipitation and Temperature.] {{Webarchive|url=https://web.archive.org/web/20080412000000/https://web.archive.org/web/20080412152736/http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/us_impacts/ustp_impacts.shtml |date=12 April 2008 }} Retrieved on 16 April 2008.</ref> The northern tier of the lower 48 exhibits above normal temperatures during the fall and winter, while the Gulf coast experiences below normal temperatures during the winter season.<ref>[[Climate Prediction Center]]. [http://www.cpc.ncep.noaa.gov/products/predictions/threats2/enso/elnino/UStrank/ond.gif Average October–December (3-month) Temperature Rankings During ENSO Events.] {{Webarchive|url=https://web.archive.org/web/20080530032315/http://www.cpc.ncep.noaa.gov/products/predictions/threats2/enso/elnino/UStrank/ond.gif |date=30 May 2008 }} Retrieved on 16 April 2008.</ref><ref>[[Climate Prediction Center]]. [http://www.cpc.ncep.noaa.gov/products/predictions/threats2/enso/elnino/UStrank/djf.gif Average December–February (3-month) Temperature Rankings During ENSO Events.] {{Webarchive|url=https://web.archive.org/web/20080530032314/http://www.cpc.ncep.noaa.gov/products/predictions/threats2/enso/elnino/UStrank/djf.gif |date=30 May 2008 }} Retrieved on 16 April 2008.</ref> The subtropical jet stream across the deep [[tropics]] of the northern hemisphere is enhanced due to increased convection in the equatorial Pacific, which decreases [[tropical cyclogenesis]] within the Atlantic tropics below what is normal, and increases tropical cyclone activity across the eastern Pacific.<ref name="ENSO TC influence FAQ">{{Cite web|url=http://www.cpc.noaa.gov/products/analysis_monitoring/ensostuff/ensofaq.shtml#HURRICANES|publisher=[[Climate Prediction Center]]|format=FAQ|access-date=21 March 2008|title=How do El Niño and La Nina influence the Atlantic and Pacific hurricane seasons?|archive-url=https://web.archive.org/web/20090827143632/http://www.cpc.noaa.gov/products/analysis_monitoring/ensostuff/ensofaq.shtml#HURRICANES|archive-date=27 August 2009|url-status=dead}}</ref> In the southern hemisphere, the subtropical jet stream is displaced equatorward, or north, of its normal position, which diverts frontal systems and thunderstorm complexes from reaching central portions of the continent.<ref name="Caio"/>

====La Niña====
Across North America during [[La Niña]], increased precipitation is diverted into the [[Pacific Northwest]] due to a more northerly storm track and jet stream.<ref>Nathan Mantua. [http://www.ccb.ucar.edu/lanina/report/mantua.html La Niña Impacts in the Pacific Northwest.] {{webarchive|url=https://web.archive.org/web/20071022030057/http://www.ccb.ucar.edu/lanina/report/mantua.html |date=22 October 2007 }} Retrieved on 29 February 2008.</ref> The storm track shifts far enough northward to bring wetter than normal conditions (in the form of increased snowfall) to the Midwestern states, as well as hot and dry summers.<ref>Southeast Climate Consortium. [http://www.agclimate.org/Development/apps/agClimate/controller/perl/agClimate.pl/agClimate.pl?function=climforecast/outlook.html&location=local&type SECC Winter Climate Outlook.] {{webarchive|url=https://web.archive.org/web/20080304212445/http://www.agclimate.org/Development/apps/agClimate/controller/perl/agClimate.pl/agClimate.pl?function=climforecast%2Foutlook.html&location=local&type |date= 4 March 2008 }} Retrieved on 29 February 2008.</ref><ref>[[Reuters]]. [https://www.reuters.com/article/domesticNews/idUSN1619766420070216 La Nina could mean dry summer in Midwest and Plains.] {{Webarchive|url=https://web.archive.org/web/20080421224855/http://www.reuters.com/article/domesticNews/idUSN1619766420070216 |date=21 April 2008 }} Retrieved on 29 February 2008.</ref> Snowfall is above normal across the Pacific Northwest and western Great Lakes.<ref name="cpc.ncep.noaa.gov"/> Across the North Atlantic, the jet stream is stronger than normal, which directs stronger systems with increased precipitation towards Europe.<ref>Paul Simons and Simon de Bruxelles. [http://www.timesonline.co.uk/tol/news/environment/article3200801.ece More rain and more floods as La Niña sweeps across the globe.]{{dead link|date=September 2024|bot=medic}}{{cbignore|bot=medic}} Retrieved on 13 May 2008.</ref>

===Dust Bowl===
Evidence suggests the jet stream was at least partly responsible for the widespread drought conditions during the 1930s [[Dust Bowl]] in the Midwest United States. Normally, the jet stream flows east over the [[Gulf of Mexico]] and turns northward pulling up moisture and dumping [[rain]] onto the [[Great Plains]]. During the Dust Bowl, the jet stream weakened and changed course traveling farther south than normal. This starved the Great Plains and other areas of the Midwest of rainfall, causing extraordinary drought conditions.<ref>{{Cite web|url=https://www.thoughtco.com/1930s-dust-bowl-drought-3444382|title=What Caused the U.S. Dust Bowl Drought of the 1930s?|last=Oblack|first=Rachelle|website=ThoughtCo|language=en|access-date=2019-07-02|archive-date=2 July 2019|archive-url=https://web.archive.org/web/20190702152954/https://www.thoughtco.com/1930s-dust-bowl-drought-3444382|url-status=live}}</ref>