Jet streams are fast flowing, narrow air currents in the atmosphere. It is the physical mechanism of a teleconnection. The main terrestrial jet streams are located near the altitude of the tropopause and are westerly winds, flowing west to east around the globe. The Northern Hemisphere and the Southern Hemisphere each have a polar jet around their respective polar vortex at around above sea level and typically travelling at around although often considerably faster. Closer to the equator, somewhat higher and somewhat weaker, is a subtropical jet.
The northern polar jet flows over the middle to northern latitudes of North America, Europe, and Asia and their intervening oceans, while the southern hemisphere polar jet mostly circles Antarctica. Jet streams may start, stop, split into two or more parts, combine into one stream, or flow in various directions including opposite to the direction of the remainder of the jet.
The El Niño–Southern Oscillation affects the location of the jet streams, which in turn affects the weather over the tropical Pacific Ocean and affects the climate of much of the tropics and subtropics, and can affect weather in higher-latitude regions. The term "jet stream" is also applied to some other winds at varying levels in the atmosphere, some global (such as the higher-level polar-night jet), some local (such as the African easterly jet). Meteorologists use the location of some of the jet streams as an aid in weather forecasting. Airlines use them to reduce some flight times and fuel consumption. Scientists have considered whether the jet streams might be harnessed for power generation. In World War II, the Japanese used the jet stream to carry Fu-Go balloon bombs across the Pacific Ocean to launch small attacks on North America.
Jet streams have been detected in the atmospheres of Venus, Jupiter, Saturn, Uranus, and Neptune.
Discovery The first indications of this phenomenon came from American professor Elias Loomis (1811–1889), when he proposed the hypothesis of a powerful air current in the upper air blowing west to east across the United States as an explanation for the behaviour of major storms.Sunny Intervals and Showers: our changing weather, p.142; Weidenfeld & Nicolson, London, 1992. After the 1883 eruption of the Krakatoa volcano, weather watchers tracked and mapped the effects on the sky over several years. They labelled the phenomenon the "equatorial smoke stream".See: Bishop, Sereno E. (17 January 1884) "Letters to the Editor: The remarkable sunsets," Nature, 29: 259–260; on page 260, Bishop speculates that a rapid current in the upper atmosphere was carrying the dust from the eruption of Krakatau westward around the equator. Bishop, S.E. (May 1884) "The equatorial smoke-stream from Krakatoa," The Hawaiian Monthly, vol. 1, no. 5, pages 106–110. Bishop, S.E. (29 January 1885) "Letters to the Editor: Krakatoa," Nature, vol. 31, pages 288–289. Rev. Sereno E. Bishop (1886) "The origin of the red glows," American Meteorological Journal, vol. 3, pages 127–136, 193–196; on pages 133–136, Bishop discusses the "equatorial smoke stream" that was produced by the eruption of Krakatau. Hamilton, Kevin (2012) "Sereno Bishop, Rollo Russell, Bishop's Ring and the discovery of the "Krakatoa easterlies"," Atmosphere-Ocean, vol. 50, no. 2, pages 169–175. Krakatoa Committee of the Royal Society [of London], The Eruption of Krakatoa and Subsequent Phenomena (London, England: Harrison and Sons, 1888). Evidence of an equatorial high-speed, high-altitude current (the quasi-biennial oscillation) is presented in the following sections: Part IV., Section II. General list of dates of first appearance of all the optical phenomena. By the Hon. Rollo Russell., pages 263–312. Part IV., Section III. (A). General geographic distribution of all the optical phenomena in space and time; including also velocity of translation of smoke stream. By the Hon. Rollo Russell., pages 312–326. Part IV., Section III. (B). The connection between the propagation of the sky haze with its accompanying optical phenomena, and the general circulation of the atmosphere. By Mr. E. Douglas Archibald., pages 326–334; that Rev. S.E. Bishop of Honolulu first noticed a westward circulation of dust from Krakatau is acknowledged on page 333. Part IV., Section III. (C). Spread of the phenomena round the world, with maps illustrative thereof. By the Hon. Rollo Russell., pages 334–339; after page 334 there are map inserts, showing the progressive spread, along the equator, of the dust from Krakatau. In the 1920s Japanese meteorologist Wasaburo Oishi detected the jet stream from a site near Mount Fuji.Ooishi, W. (1926) Raporto de la Aerologia Observatorio de Tateno (in Esperanto). Aerological Observatory Report 1, Central Meteorological Observatory, Japan, 213 pages. He tracked pilot balloons ("pibals"), used to measure wind speed and direction, as they rose in the air. Oishi's work largely went unnoticed outside Japan because it was published in Esperanto, though chronologically he has to be credited for the scientific discovery of jet streams. American pilot Wiley Post (1898–1935), the first man to fly around the world solo in 1933, is often given some credit for discovery of jet streams. Post invented a pressurized suit that let him fly above . 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.
German meteorologist Heinrich Seilkopf is credited with coining a special term, Strahlströmung (literally "jet current"), for the phenomenon in 1939.Seilkopf, H., Maritime meteorologie, which is volume II of: R. Habermehl, ed., Handbuch der Fliegenwetterkunde [Handbook of Aeronautical Meteorology] (Berlin, Germany: Gebrüder Radetzke [Radetzke Brothers], 1939); Seilkopf coins the word "Strahlströmung" on page 142 and discusses the jet stream on pages 142–150.Arbeiten zur allgemeinen Klimatologie by Hermann Flohn p. 47 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 westerly tailwinds in excess of in flights, for example, from the US to the UK. Similarly in 1944 a team of American meteorologists in Guam, including Reid Bryson, had enough observations to forecast very high west winds that would slow bombers raiding Japan.
Description
The polar and subtropical jet streams are the product of two factors: the atmospheric heating by solar radiation that produces the large-scale 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 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.
Polar jet streams are typically located near the 250 hPa (about 1/4 atmosphere) pressure level, or above sea level while the weaker subtropical jet streams are somewhat higher.
The polar jets, at lower altitude, and often intruding into mid-latitudes, strongly affect weather and aviation.David R. Cook Jet Stream Behavior. Retrieved on 8 May 2008.B. Geerts and E. Linacre. The Height of the Tropopause. Retrieved on 8 May 2008. 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.National Weather Service JetStream. The Jet Stream. Retrieved on 8 May 2008.McDougal Littell. Paths of Polar and Subtropical Jet Streams. Retrieved on 13 May 2008.
The width of a jet stream is typically a few hundred kilometres or miles and its vertical thickness often less than .
Jet streams are typically continuous over long distances, but discontinuities are also common.Glossary of Meteorology. Jet Stream. Retrieved on 8 May 2008. 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.
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. Shortwave troughs, are smaller scale waves superimposed on the Rossby waves, with a scale of long,Glossary of Meteorology. Cyclone wave. Retrieved on 13 May 2008. that move along through the flow pattern around large scale, or longwave, "ridges" and "troughs" within Rossby waves.Glossary of Meteorology. Short wave. Retrieved on 13 May 2008.
The wind speeds are greatest where temperature differences between air masses are greatest, and often exceed . Speeds of have been measured.
The jet stream moves from west to east bringing changes of weather. 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.Blackburn, Mike; Hoskins, Brian; Slingo, Julia:
The jet stream serves as an atmospheric boundary, separating the cold polar air from the warm subtropical air. Its instability is characterized by the winding of Rossby waves, which may lead to harsh winter weather; For example, in early 2026, extreme cold air erupted across North America, causing temperatures in areas such as Ontario to drop below .
Cause
In general, winds are strongest immediately under the tropopause (except locally, during tornadoes, tropical cyclones or other anomalous situations). If two air masses of different temperatures or densities meet, the resulting pressure difference caused by the density difference (which ultimately 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.John P. Stimac. Air pressure and wind. Retrieved on 8 May 2008.