Jet stream 16472 225327937 2008-07-13T03:06:15Z Pekpeklover 7431407 /* Uses */ edited typo error; changed Pam Am to Pan Am {{otheruses2|jet stream}} [[Image:Jet Stream.jpg|thumb|250px|Jet streams flow from the west in the upper portion of the troposphere]] '''Jet streams''' are fast flowing, relatively narrow [[thermal wind|air current]]s found at the [[tropopause]], the transition between the [[troposphere]] (where temperature decreases with height) and the [[stratosphere]] (where temperature increases with height),<ref>[[United States Department of Energy]] 26 June 2002. [http://www.newton.dep.anl.gov/askasci/wea00/wea00135.htm Ask a Scientist.] Retrieved on [[2008-05-05]].</ref> and are located at 10-15&nbsp;kilometers above the surface of the [[Earth]]. They form near boundaries of adjacent air masses with significant differences in [[temperature]], such as the [[polar region]] and the warmer air to the south.<ref>[[University of Illinois]]. [http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cyc/upa/jet.rxml Jet Stream.] Retrieved on [[2008-05-04]].</ref> The path of the jet typically has a [[meander]]ing shape, and these meanders known as [[Rossby waves]]. Rossby waves propagate westward with respect to the flow in which they are embedded, which translates to a slower eastward migration across the globe than smaller scale [[shortwave (meteorology)|short wave troughs]]. The major jet streams are westerly winds (flowing west to east) in the [[Northern Hemisphere]]. During the [[summer]], low-level easterly jets can form in tropical regions. A southerly low level jet in the [[Great Plains]] of North America helps fuel overnight [[thunderstorm]] activity, normally in the form of [[mesoscale convective system]]s. A similar northerly low-level jet can form across [[Australia]], instigated by cut-off lows which develop across southwest portions of the country. Meteorologists use the location of the jet stream as an aid in [[weather forecasting]]. The main commercial use of the jet stream is during airline travel, as flight time can be dramatically affected by either flying with or against the stream. One type of [[clear-air turbulence]] is found in the jet stream's vicinity, which can be a hazard to aircraft. One future benefit of the jet stream could be to power [[airborne wind turbine]]s, if technological hurdles can be overcome. ==Discovery== The existence of the jet stream may have been first detected in the 1920s by Japanese meteorologist Wasaburo Ooishi.<ref>John M. Lewis. [http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2FBAMS-84-3-357 Ooishi's Observation: Viewed in the Context of Jet Stream Discovery.] Retrieved on [[2008-05-08]].</ref> From a site near [[Mount Fuji]], he tracked pilot balloons, also known as pibals (balloons used to determine upper level winds using a [[theodolite]] and the balloon's known ascension rate due to its internal gas),<ref>Martin Brenner. [http://www.csulb.edu/~mbrenner/balloon.htm Pilot Balloon Resources.] Retrieved on [[2008-05-13]].</ref> as they rose into the atmosphere. Ooishi's work largely went unnoticed outside of Japan. American pilot [[Wiley Post]], the first man to fly around the world solo in 1933, is often given some credit for discovery of the jet stream. Post invented a pressurized suit that let him fly above {{convert|6200|m|ft}}. In the year before his death, Post made several attempts at a high-altitude transcontinental flight, and noticed that at times his ground speed greatly exceeded his air speed.<ref>Acepilots.com. [http://www.acepilots.com/post.html Wiley Post.] Retrieved on [[2008-05-08]].</ref> German meteorologist H. Seilkopf is credited with coining the term "jet stream" (Strahlströmmung) in a 1939 paper.<ref>[http://www.aos.princeton.edu/WWWPUBLIC/gkv/history/Lewis-on-Phillips98.pdf John M. Lewis: Clarifying the Dynamics of the General Circulation: Phillips’s 1956 Experiment] from: Bulletin of the American Meterological Society, Vol. 79, No. 1, January 1988</ref> Many sources credit real understanding of the nature of jet streams to regular and repeated flight-path traversals during [[World War II]]. Flyers consistently noticed tailwinds in excess of 100 mph in flights, for example, between the US and UK.<ref>[[BBC]]. [http://www.bbc.co.uk/weather/features/basics_jetstreams.shtml Weather Basics - Jet Streams.] Retrieved on [[2008-05-08]].</ref> ==Description== [[Image:Jetcrosssection.jpg|thumb|right|250 px|Cross section of the subtropical and polar jet streams by latitude]] There are two main jet streams north of subtropical [[latitude]]s, with a weaker [[subtropical]] stream closer to the [[equator]]. The polar jet stream is typically located near the 250&nbsp;[[Pascal (unit)|hPa]] (7.38&nbsp;[[Inch of mercury|inHg]]) pressure level, or {{convert|7|km|mi}} to {{convert|12|km|mi}} above [[sea level]], while the subtropical jet is much higher, between {{convert|10|km|mi}} and {{convert|16|km|mi}} above sea level. Both upper-level jet streams form near breaks in the tropopause, which is at a higher altitude near the equator than it is over the poles, with large changes in its height occurring near the location of the jet stream.<ref name="COOK">David R. Cook [http://www.newton.dep.anl.gov/askasci/wea00/wea00067.htm Jet Stream Behavior.] Retrieved on [[2008-05-08]].</ref><ref>B. Geerts and E. Linacre. [http://www-das.uwyo.edu/~geerts/cwx/notes/chap01/tropo.html The Height of the Tropopause.] Retrieved on [[2008-05-08]].</ref> The streams are most commonly found between latitudes 30°N and 60°N, with the subtropical jet stream located close to latitude 30°N. The upper level jet stream is said to "follow the sun" as it moves northward during the warm season, or late [[spring (season)|spring]] and [[summer]], and southward during the cold season, or [[autumn]] and [[winter]].<ref>[[National Weather Service]] JetStream. [http://www.srh.noaa.gov/jetstream//global/jet.htm The Jet Stream.] Retrieved on [[2008-05-08]].</ref><ref>McDougal Littell. [http://www.classzone.com/books/earth_science/terc/content/investigations/es1908/es1908page04.cfm Paths of Polar and Subtropical Jet Streams.] Retrieved on [[2008-05-13]].</ref> Jet streams are typically continuous over long distances, but discontinuities are common.<ref name="GOMdef">Glossary of Meteorology. [http://amsglossary.allenpress.com/glossary/search?id=jet-stream1 Jet Stream.] Retrieved on [[2008-05-08]].</ref> The path of the jet typically has a meandering shape, and these meanders themselves propagate east, at lower speeds than that of the actual [[wind]] within the flow. Each large meander, or wave, within the jet stream is known as a Rossby wave. Rossby waves are caused by changes in the [[Coriolis effect]] with latitude, and propagate westward with respect to the flow in which they are embedded, which slows down the eastward migration of upper level troughs and ridges across the globe when compared to their embedded shortwave troughs.<ref>Glossary of Meteorology. [http://amsglossary.allenpress.com/glossary/search?id=rossby-wave1 Rossby Wave.] Retrieved on [[2008-05-13]].</ref> Shortwave troughs are smaller packets of upper level energy, on the scale of {{convert|1000|km|mi}} to {{convert|4000|km|mi}} long,<ref>Glossary of Meteorology. [http://amsglossary.allenpress.com/glossary/search?id=cyclone-wave1 Cyclone wave.] Retrieved on [[2008-05-13]].</ref> which move 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.] Retrieved on [[2008-05-13]].</ref> Jet streams can split into two due to the formation of an upper-level closed low, which diverts a portion of the jet stream under its base, while the remainder of the jet moves by to its north. The wind speeds vary according to the temperature [[gradient]], exceeding {{convert|92|km/h|kn}},<ref name="GOMdef">Glossary of Meteorology. [http://amsglossary.allenpress.com/glossary/search?id=jet-stream1 Jet Stream.] Retrieved on [[2008-05-08]].</ref> although speeds of over {{convert|398|km/h|kn}} have been measured.<ref name="ROBROY">Robert Roy Britt. [http://www.space.com/scienceastronomy/solarsystem/jupiter_sidebar_000209.html et Streams On Earth and Jupiter.] Retrieved on [[2008-05-04]].</ref> Meteorologists now understand that the path of the jet stream steers 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, [[united kingdom| Britain]] experienced severe flooding as a result of the polar jet staying south for the summer.<ref>{{cite web |title = Why has it been so wet? |publisher = BBC |date = 23 July 2007 |url = http://news.bbc.co.uk/1/hi/magazine/6911918.stm |accessdate = 2007-07-31 }}</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 |accessdate = 2007-08-29 |format = PDF }}</ref> ==Cause== ===Upper-level variety=== [[Image:Jetstreamconfig.jpg|thumb|right|250 px|General configuration of the polar and subtropical jet streams]] {{See also|Extratropical cyclone|Thermal wind}} In general, winds are strongest just under the tropopause (except during [[tornado]]es, [[hurricane]]s or other anomalous situations). If two air masses of different temperatures or densities meet, the resulting pressure difference caused by the density difference (which causes wind) is highest within the transition zone. The wind does not flow directly from the hot to the cold area, but is deflected by the Coriolis effect and flows along the boundary of the two air masses.<ref name="Stimac">John P. Stimac. [http://www.ux1.eiu.edu/~cfjps/1400/pressure_wind.html Air pressure and wind.] Retrieved on [[2008-05-08]].</ref> The [[polar front]] and [[Subtropical jet stream|subtropical jets]] merge at some locations and times, while at other times they are well separated. All these facts are consequences of the [[thermal wind]] relation. The balance of forces on an atmospheric parcel in the vertical direction is primarily between the pressure gradient and the force of gravity, a balance referred to as [[hydrostatic]]. In the horizontal, the dominant balance outside of the tropics is between the Coriolis effect and the pressure gradient, a balance referred to as [[geostrophic]]. Given both hydrostatic and geostrophic balance, one can derive the thermal wind relation: the vertical derivative of the horizontal wind is proportional to the horizontal temperature gradient. The sense of the relation is such that temperatures decreasing polewards implies that winds develop a larger eastward component as one moves upwards. Therefore, the strong eastward moving jet streams are in part a simple consequence of the fact that the equator is warmer than the north and south poles.<ref name="Stimac">John P. Stimac. [http://www.ux1.eiu.edu/~cfjps/1400/pressure_wind.html Air pressure and wind.] Retrieved on [[2008-05-08]].</ref> The thermal wind relation does not immediately provide an explanation for why the winds are organized in tight jets, rather than distributed more broadly over the hemisphere. There are two factors that contribute to this sharpness of the jets. One is the tendency for developing cyclonic disturbances in midlatitudes to form [[Surface_weather_analysis#Fronts|fronts]]. A front is a sharp localized gradient in temperature. The polar front jet stream can be thought of as the result of this [[frontogenesis]] process in midlatitudes, as the storms concentrate the north-south temperature contrast into relatively narrow regions.<ref name="GOMdef">Glossary of Meteorology. [http://amsglossary.allenpress.com/glossary/search?id=jet-stream1 Jet Stream.] Retrieved on [[2008-05-08]].</ref> An alternative explanation is more appropriate for the subtropical jet, which forms at the poleward limit of the tropical [[Hadley cell]]. One can visualize this circulation as being symmetric with respect to longitude. Rings of air encircling the Earth move polewards beneath the [[tropopause]] from the equator into the subtropics. As they do so they tend to conserve their angular momentum. But they are also moving closer to the axis of rotation, so they must spin faster in the direction of rotation, implying an increased eastward component of the winds.<ref>[[Lyndon State College]] Meteorology. [http://apollo.lsc.vsc.edu/classes/met130/notes/chapter10/subt_jet_form.html Jet Stream Formation - Subtropical Jet.] Retrieved on [[2008-05-08]].</ref> [[Jupiter]]'s atmosphere has multiple jet streams, forming the familiar banded color structure, caused by internal heating.<ref name="ROBROY">Robert Roy Britt. [http://www.space.com/scienceastronomy/solarsystem/jupiter_sidebar_000209.html et Streams On Earth and Jupiter.] Retrieved on [[2008-05-04]].</ref> The factors that control the number of jet streams in a planetary atmosphere is an active area of research in dynamical meteorology. In models, as one increases the planetary radius, holding all other parameters fixed, the number of jet streams increases. ===Low-level variety=== There are low-level wind maxima in the atmosphere that are referred to as jets, such as the [[African easterly jet]] which occurs during the Northern Hemisphere [[summer]] between 10°N and 20°N from the [[Indian Ocean]] across [[Africa]], and the nocturnal poleward [[low-level jet]] in the [[Great Plains]]. The easterly jet out of Africa is formed because of heating of the Tibetan plateau and subsequent [[anticyclogenesis]].<ref>Dr. Alex DeCaria. [http://snowball.millersville.edu/~adecaria/ESCI344/esci344_lesson04_seasonal_mean_wind_fields.html Lesson 4 – Seasonal-mean Wind Fields.] Retrieved on [[2008-05-03]].</ref> The equatorward divergence takes the form of easterlies, embedded in the form of easterly jets. This jet stream is considered to play a crucial role in the southwest [[monsoon]] of Africa,<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.] Retrieved on [[2008-05-08]].</ref> and helps form the [[tropical wave]]s which march 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 ?] Retrieved on [[2008-05-08]].</ref> A southerly low-level jet in the Great Plains 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.] Retrieved on [[2008-05-08]].</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. [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 [[2008-05-08]].</ref> ==Uses== ===Airplanes=== [[Image:Greatcircle Jetstream routes.svg|thumb|250px|Flights to and from [[Tokyo]] and [[Los Angeles, California|Los Angeles]] using the jet stream eastbound and a [[great circle]] route westbound.]] The location of the jet stream is extremely important for [[airline]]s. Commercial use of the jet stream began on [[November 18]], [[1952]], when Pan Am flew from Tokyo to Honolulu at an altitude of {{convert|7600|m|ft}}. It cut the trip time by over one-third, from 18 to 11.5 hours.<ref>M. D. Klaas. [http://findarticles.com/p/articles/mi_qa3901/is_200006/ai_n8911736/pg_2 Stratocruiser: Part three.] Retrieved on [[2008-05-08]].</ref> Not only does it cut time off the flight, it also nets fuel savings for the airline industry.<ref>Ned Rozell. [http://www.gi.alaska.edu/ScienceForum/ASF17/1727.html Amazing flying machines allow time travel.] Retrieved on [[2008-05-08]].</ref> Within North America, the time needed to fly east across the [[continent]] can be decreased by about 30 [[minute]]s if an [[fixed-wing aircraft|airplane]] can fly with the jet stream, or increased by more than that amount if it must fly west against it. Associated with jet streams is a phenomenon known as [[clear air turbulence]] (CAT), caused by vertical and horizontal [[windshear]] connected to the jet streams.<ref>[[BBC]]. [http://www.bbc.co.uk/weather/features/understanding/jetstreams_uk.shtml Jet Streams in the UK.] Retrieved on [[2008-05-08]].</ref> The CAT is strongest on the cold [[air]] side of the jet,<ref>M. P. de Villiers and J. van Heerden. [http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=73339 Clear air turbulence over South Africa.] Retrieved on [[2008-05-08]].</ref> next to and just underneath the axis of the jet.<ref>CLARK T. L., HALL W. D., KERR R. M., MIDDLETON D., RADKE L., RALPH F. M., NEIMAN P. J., LEVINSON D. [http://cat.inist.fr/?aModele=afficheN&cpsidt=1345004 Origins of aircraft-damaging clear-air turbulence during the 9 December 1992 Colorado downslope windstorm : Numerical simulations and comparison with observations.] Retrieved on [[2008-05-08]].</ref> Clear air turbulence can be hazardous to aircraft, and has caused fatal accidents, such as with [[BOAC Flight 911]] and [[United Airlines Flight 826]].<ref>Aviation Safety Network. [http://aviation-safety.net/database/record.php?id=19660305-1 Accident Description for BOAC Flight 911.] Retrieved on [[2008-05-13]].</ref><ref>[[National Transportation Safety Board]]. [http://www.ntsb.gov/Pressrel/1997/971230.htm Aircraft Accident Investigation United Airlines flight 826, Pacific Ocean December 28, 1997.] Retrieved on [[2008-05-13]].</ref><ref name="CNN UAF826">{{cite news | url = http://www.cnn.com/US/9712/29/united.turbulence/ | title = NTSB investigates United Airlines plunge | author = Staff writer | publisher = [[CNN]] | date = [[December 29]], [[1997]] | accessdate = 2008-05-13}}</ref> ===Future power generation=== Scientists are investigating ways to harness the wind energy within the jet stream using [[airborne wind turbine]]s. Kite-like wind generators have been proposed, which would transmit its electricity back to the ground via either aluminum cables, copper cables, or beams of microwave energy. Tethered balloons, which reach heights of {{convert|4500|m|ft}} have been used to monitor drug trafficking over many years, with no reported airplane incidents. According to one estimate, only 1&nbsp;percent of the potential wind energy in the jet stream could meet the world's current energy needs. The required technology would reportedly take 10–20 years to develop.<ref>Keay Davidson. [http://www.sfgate.com/cgi-bin/article.cgi?file=/c/a/2007/05/07/MNGNEPMD801.DTL Scientists look high in the sky for power.] Retrieved on [[2008-05-08]].</ref> ==Changes due to climate cycles== ===Effects of ENSO=== [[Image:El nino north american weather.png|thumb|right|250 px|Impact of El Niño and La Niña on North America]] {{Main article|Effects of the El Niño-Southern Oscillation in the United States}} The changing of the normal location of upper-level jet streams can be anticipated during phases of the [[El Niño-Southern Oscillation]] (ENSO), which leads to consequences precipitation-wise and temperature-wise across North America, affects [[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.] Retrieved on [[2008-05-13]].</ref> Changes in ENSO also change the location of the jet stream over [[South America]], which partially effects 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.] Retrieved on [[2008-05-13]].</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.] Retrieved on [[2008-02-28]].</ref> During the El 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.] Retrieved on [[2008-02-28]].</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>[[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.] Retrieved on [[2008-04-16]].</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.] Retrieved on [[2008-04-16]].</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.] Retrieved on [[2008-04-16]].</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|accessdate=2008-03-21|title=How do El Niño and La Nina influence the Atlantic and Pacific hurricane seasons?}}</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">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.] Retrieved on [[2008-05-13]].</ref> ====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.] Retrieved on [[2008-02-29]].</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.] Retrieved on [[2008-02-29]].</ref><ref>[[Reuters]]. [http://www.reuters.com/article/domesticNews/idUSN1619766420070216 La Nina could mean dry summer in Midwest and Plains.] Retrieved on [[2008-02-29]].</ref> Snowfall is above normal across the Pacific Northwest and western Great Lakes.<ref>[[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.] Retrieved on [[2008-04-16]].</ref> 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.] Retrieved on [[2008-05-13]].</ref> ===Global warming=== {{Main article|Global warming}} Between 1979 and 2001, it has been found that the position of the jet stream has been moving northward at a rate of {{convert|2.01|km|mi}} per year across the [[Northern Hemisphere]]. Across [[North America]], this type of change could lead to drier conditions across the southern tier of the [[United States]] and more frequent and more intense [[tropical cyclone]]s in the tropics. A similar slow poleward drift was found when studying the [[Southern Hemisphere]] jet stream over the same time frame.<ref>[[Associated Press]]. [http://www.komotv.com/news/17918694.html Jet stream found to be permanently drifting north.] Retrieved on [[2008-05-08]].</ref> ===The Dust Bowl=== {{Main article|Dust Bowl}} Evidence suggests the jet stream was at least partially responsible for the wide drought conditions during the 1930s [[Dust Bowl]] in the Midwest United States. Normally, the jet stream flows west 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 precious rain creating dusty conditions.<ref>[[Weather at About.com]]. [http://weather.about.com/od/weatherfaqs/f/dustbowl.html Causes of the Dust Bowl in the United States.] Retrieved on [[2008-06-10]].</ref> ==See also== *[[Surface weather analysis]] *[[Tornado]] *[[Wind shear]] *[[Fire balloon|Japanese balloon bombing of the United States during World War II]] *[[Sting jet]] ==References== {{reflist}} ==External links== *[http://squall.sfsu.edu/crws/jetstream.html Graphics and movies of the current jet streams.] *[http://ams.allenpress.com/amsonline/?request=get-abstract&doi=10.1175%2FBAMS-84-3-357 John M. Lewis. (2001). Ooishi's Observation: Viewed in the Context of Jet Stream Discovery. National Severe Storms Laboratory.] {{Earthsatmosphere}} [[Category:Atmospheric dynamics]] [[Category:Basic meteorological concepts and phenomena]] [[Category:winds]] [[Category:Jet]] [[bg:Струйно течение]] [[ca:Corrent en jet]] [[cs:Tryskové proudění]] [[da:Jetstrøm]] [[de:Jetstream]] [[et:Jugavool]] [[el:Αεροχείμαρρος]] [[es:Corriente en chorro]] [[fa:جت استریم]] [[fr:Courant-jet]] [[ga:Scairdsruth]] [[gl:Corrente de jet]] [[ko:제트 기류]] [[it:Corrente a getto]] [[he:זרם סילון]] [[nl:Straalstroom]] [[ja:ジェット気流]] [[no:Jetstrømmer]] [[nn:Jetstraum]] [[pl:Prąd strumieniowy]] [[pt:Jet stream]] [[ru:Высотное струйное течение]] [[fi:Suihkuvirtaus]] [[sv:Jetström]] [[tr:Jet stream]] [[zh:高速氣流]]