View source for Polar vortex

{{Not to be confused| Polar low}}
{{Short description|Persistent cold-core low-pressure area that circles one of the poles}}
{{For|[[Shani Mootoo]]'s novel|Polar Vortex}}
{{Multiple image
| header    = The Arctic tropospheric polar vortex
| header_align = center
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| align     = right
| image1    = November2013 polar vortex geopotentialheight mean Large.jpg
| width1      = 149
| alt1      = Map of a compact blob over the Arctic
| caption1  = A strong [[tropospheric]] polar vortex configuration in November 2013
| image2    = Jan52014 polar vortex geopotentialheight mean Large.jpg
| width2      = 149
| alt2      = Map of a blobs spreading from the Arcitc
| caption2  = A more typical weak tropospheric polar vortex on January 5, 2014
}}

A '''polar vortex''', more formally a '''circumpolar vortex''', is a large region of cold, rotating air; polar vortices encircle both of Earth's [[Polar regions of Earth|polar regions]]. Polar vortices also exist on other rotating, low-[[Axial tilt|obliquity]] [[Planet#Planetary-mass objects |planetary bodies]].<ref>{{cite journal |url=http://doi.org/10.1016/j.pss.2010.04.024 |date=August 2011 |journal=Planetary and Space Science |title=Dynamics and circulation regimes of terrestrial planets |pages=900–914 |first1=P.L. |last1=Read |volume=59 |issue=10 |doi=10.1016/j.pss.2010.04.024 |bibcode=2011P&SS...59..900R|url-access=subscription }}</ref> The term polar vortex can be used to describe two distinct phenomena; the [[stratosphere|stratospheric]] polar vortex, and the [[troposphere|tropospheric]] polar vortex. The stratospheric and tropospheric polar vortices both rotate in the direction of the Earth's spin, but they are distinct phenomena that have different sizes, structures, seasonal cycles, and impacts on weather.

The stratospheric polar vortex is an area of high-speed, [[cyclonic rotation|cyclonically]] rotating winds around 15&nbsp;km to 50&nbsp;km high, poleward of 50°, and is strongest in winter. It forms during autumn when Arctic or Antarctic temperatures cool rapidly as the [[polar night]] begins. The increased temperature difference between the pole and the tropics causes strong winds, and the [[Coriolis effect]] causes the vortex to spin up. The stratospheric polar vortex breaks down during spring as the polar night ends. A [[sudden stratospheric warming]] (SSW) is an event that occurs when the stratospheric vortex breaks down during winter, and can have significant [[Sudden stratospheric warming#Weather effects|impacts on surface weather]].{{citation needed|date=March 2021}}

The tropospheric polar vortex is often defined as the area poleward of the tropospheric [[jet stream]]. The equatorward edge is around 40° to 50°, and it extends from the surface up to around 10&nbsp;km to 15&nbsp;km. Its yearly cycle differs from the stratospheric vortex because the tropospheric vortex exists all year, but is similar to the stratospheric vortex since it is also strongest in winter when the polar regions are coldest.

The tropospheric polar vortex was first described as early as 1853.<ref>[https://books.google.com/books?id=Df4vAAAAYAAJ&pg=PA430&dq=%22polar+vortex%22 "Air Maps"], ''Littell's Living Age'' No. 495, 12 November 1853, p. 430.</ref> The stratospheric vortex's SSWs were discovered in 1952 with [[radiosonde]] observations at altitudes higher than 20&nbsp;km.<ref>{{cite press release |title=GEOS-5 Analyses and Forecasts of the Major Stratospheric Sudden Warming of January 2013 |publisher=[[Goddard Space Flight Center]] |url=http://gmao.gsfc.nasa.gov/researchhighlights/SSW/ |access-date=January 8, 2014}}</ref> The tropospheric polar vortex was mentioned frequently in the news and weather media in the [[Early 2014 North American cold wave|cold North American winter of 2013–2014]], popularizing the term as an explanation of very cold temperatures. The tropospheric vortex increased in public visibility in 2021 as a result of [[February 2021 North American cold wave|extreme frigid temperatures in the central United States]], with newspapers linking its effects to [[climate change]].<ref>{{Cite web|last=Plumer|first=Brad|date=16 February 2021|title=A Glimpse of America's Future: Climate Change Means Trouble for Power Grids|url=https://www.nytimes.com/2021/02/16/climate/texas-power-grid-failures.html|website=The New York Times}}</ref>

[[Ozone depletion]] occurs most heavily within the polar vortices – particularly over the Southern Hemisphere – reaching a maximum depletion in the spring.
[[Category:Snow or ice weather phenomena]]

==Arctic and Antarctic vortices==
===Northern Hemisphere===
When the tropospheric vortex of the Arctic is strong, it has a well defined and nearly circular shape. There is a single vortex with a [[jet stream]] that is well constrained near the [[polar front]], and the Arctic air is well contained. When this northern tropospheric vortex weakens, it breaks into two or more smaller vortices, the strongest of which are near [[Baffin Island]], [[Nunavut]], and the others over northeast [[Siberia]]. When it is very weak, the flow of Arctic air becomes more disorganized, and masses of cold Arctic air can push equatorward, bringing with them a rapid and sharp temperature drop.<ref name="glossvortex">{{cite web |website=Glossary of Meteorology |date=June 2000 |url=http://glossary.ametsoc.org/wiki/Polar_vortex |title=Polar vortex |publisher=[[American Meteorological Society]] |access-date=15 June 2008}}</ref>

A [[January–February 2019 North American cold wave|deep freeze]] that gripped much of the United States and Canada in late January 2019 was blamed in some accounts on a "polar vortex". This is not the scientifically correct use of the term polar vortex, but instead is referring to outbreaks of cold Arctic air caused by a weakened polar vortex. The US National Weather Service warned that frostbite is possible within just 10 minutes of being outside in such extreme temperatures, and hundreds of schools, colleges, and universities in the affected areas were closed. Around 21 people died in US due to severe frostbite.<ref>{{cite news|title=Casualty|work=BBC News|url=https://www.bbc.com/news/world-us-canada-47088684|date=1 Feb 2019|access-date=12 Feb 2019|language=en}}</ref><ref>{{cite web|title=Polar vortex: What is it and how does it happen? |url=https://www.bbc.com/news/av/world-47065461/polar-vortex-what-is-it-and-how-does-it-happen |date=30 Jan 2019|website=BBC video|access-date=31 Jan 2019}}</ref> States within the midwest region of the United States had windchills just above -50&nbsp;°F (-45&nbsp;°C). The polar vortex is also thought to have had effects in Europe. For example, the [[2013–14 United Kingdom winter floods]] were blamed on the polar vortex bringing severe cold in the [[Early 2014 North American cold wave|United States and Canada]].<ref>{{Cite web|url=http://climatestate.com/2014/02/09/uk-flooding-and-the-science-of-climate-change/|title=UK Flooding and the Science of Climate Change|date=9 February 2014|access-date=19 April 2019|archive-date=7 June 2019|archive-url=https://web.archive.org/web/20190607235448/http://climatestate.com/2014/02/09/uk-flooding-and-the-science-of-climate-change/|url-status=dead}}</ref> Similarly, the severe cold in the United Kingdom in the winters of [[Winter of 2009–10 in Great Britain and Ireland|2009–10]] and [[Winter of 2010–11 in Great Britain and Ireland|2010–11]] were also blamed on the polar vortex.<ref>{{Cite web|url=https://www.independent.co.uk/news/uk/home-news/polar-vortex-what-is-coldest-winter-uk-weather-cold-snap-why-arctic-met-office-a7402611.html|title = Britain is about to get very, very cold|website = [[Independent.co.uk]]|date = 7 November 2016}}</ref>

===Southern Hemisphere===
The [[Antarctic]] vortex of the [[Southern Hemisphere]] is a single low-pressure zone that is found near the edge of the [[Ross ice shelf]], near 160 west longitude. When the polar vortex is strong, the mid-latitude [[Westerlies]] (winds at the surface level between 30° and 60° latitude from the west) increase in strength and are persistent. When the polar vortex is weak, high-pressure zones of the mid-latitudes may push poleward, moving the polar vortex, [[jet stream]], and polar front equatorward. The jet stream is seen to "buckle" and deviate south. This rapidly brings cold dry air into contact with the warm, moist air of the mid-latitudes, resulting in a rapid and dramatic change of weather known as a "[[cold snap]]".<ref>{{cite press release |title=Stratospheric Polar Vortex Influences Winter Cold, Researchers Say |publisher=[[American Association for the Advancement of Science]] |date=December 3, 2001 |url=http://www.eurekalert.org/pub_releases/2001-12/uoia-spv120301.php|access-date=May 23, 2015}}</ref>

In [[Australia]], the polar vortex, known there as a "polar blast" or "polar plunge", is a [[cold front]] that drags air from [[Antarctica]] which brings rain showers, snow (typically inland, with [[blizzard]]s occurring in the highlands), gusty icy winds, and [[hail]] in the south-eastern parts of the country, such as in [[Victoria (state)|Victoria]], [[Tasmania]], the southeast coast of [[South Australia]] and the southern half of [[New South Wales]] (but only on the [[windward]] side of the [[Great Dividing Range]], whereas the leeward side will be affected by [[foehn wind]]s).<ref>{{cite web|title=Polar Blast Set To Hit Australia This Weekend, First in 15 Years |url=https://www.sciencetimes.com/articles/26982/20200821/polar-blast-australia-weekend-first-15-years.htm |date=21 Aug 2020|website=Science Times|access-date=25 September 2020}}</ref><ref>{{cite news|title='Twin peaks': Sydney prepares for double burst of polar chill |url=https://www.smh.com.au/environment/weather/twin-peaks-sydney-prepares-for-double-burst-of-polar-chill-20180509-p4ze7g.html |date=9 May 2018 |website=[[Sydney Morning Herald]]|access-date=25 September 2020}}</ref>

==Identification==
The bases of the two polar vortices are located in the middle and upper [[troposphere]] and extend into the [[stratosphere]]. Beneath that lies a large mass of cold, dense Arctic air. The interface between the cold dry air mass of the pole and the warm moist air mass farther south defines the location of the polar front. The polar front is centered roughly at 60° latitude. A polar vortex strengthens in the winter and weakens in the summer because of its dependence on the temperature difference between the equator and the poles.<ref name="HB">Halldór Björnsson. {{cite web |url=http://andvari.vedur.is/~halldor/HB/Met210old/GlobCirc.html |archive-url=https://web.archive.org/web/20100324184958/http://andvari.vedur.is/~halldor/HB/Met210old/GlobCirc.html |archive-date=March 24, 2010 |title=Global circulation |url-status=dead |access-date=September 2, 2016 }}. Veðurstofa Íslands. Retrieved on 2008-06-15.</ref>{{self-published inline|date=January 2014}}

Polar cyclones are low-pressure zones embedded within the polar air masses, and exist year-round. The stratospheric polar vortex develops at latitudes above the [[subtropical jet stream]].<ref>{{cite journal |last1=Hartmann |first1=D |last2=Schoeberl |first2=M |year=1991 |title=Mixing of polar vortex air into middle latitudes as revealed by tracer-tracer scatterplots |doi=10.1029/96JD03715 |bibcode = 1997JGR...10213119W |volume=102 |issue=D11 |journal=Journal of Geophysical Research |pages=13119|doi-access=free }}</ref> Horizontally, most polar vortices have a radius of less than {{convert|1000|km|mi}}.<ref name="pause"/> Since polar vortices exist from the stratosphere downward into the mid-troposphere,<ref name="glossvortex"/> a variety of heights/pressure levels are used to mark its position. The 50 hPa pressure surface is most often used to identify its stratospheric location.<ref>{{cite journal|url=https://www.academia.edu/223963|date=April 2010|journal=Quarterly Journal of the Royal Meteorological Society|title=The association between stratospheric weak polar vortex events and cold air outbreaks in the Northern Hemisphere|page=887|first1=Erik W.|last1=Kolstad|first2=Tarjei|last2=Breiteig|first3=Adam A.|last3=Scaife|volume=136|issue=649|bibcode=2010EGUGA..12.5739K|doi=10.1002/qj.620|arxiv=0906.0027|s2cid=119249497|access-date=2017-12-02|archive-date=2020-02-24|archive-url=https://web.archive.org/web/20200224132726/https://www.academia.edu/223963|url-status=dead}}</ref> At the level of the tropopause, the extent of closed contours of [[potential temperature]] can be used to determine its strength.  Others have used levels down to the 500 hPa pressure level (about {{convert|5460|m|ft}} above sea level during the winter) to identify the polar vortex.<ref>{{cite journal|url=http://www.ccsenet.org/journal/index.php/jgg/article/viewFile/28960/18761|journal=Journal of Geology and Geography|date=2013-11-22|author=Abdolreza Kashki & Javad Khoshhal|title=Investigation of the Role of Polar Vortex in Iranian First and Last Snowfalls|issn=1916-9779|volume=5|number=4|access-date=2014-01-30|archive-date=2016-03-04|archive-url=https://web.archive.org/web/20160304065215/http://www.ccsenet.org/journal/index.php/jgg/article/viewFile/28960/18761|url-status=dead}}</ref>

==Duration and strength==
[[File:Polarvortexwinter.jpg|thumb|upright=1.75|Polar vortex and weather impacts due to {{clarification needed span|text=stratospheric warming|reason=What is "stratospheric warming"?  Please provide a wikilink to appropriate content here, or a brief explanation with a reliable citation|date=February 2025}}]]

Polar vortices are weakest during summer and strongest during winter. [[Extratropical cyclone]]s that migrate into higher latitudes when the polar vortex is weak can disrupt the single vortex creating smaller vortices ([[cold-core low]]s) within the polar air mass.<ref>{{cite book|url=https://books.google.com/books?id=-tBa1DWYoDIC&pg=PA167|page=174|title=Polar lows: mesoscale weather systems in the polar regions|author=Erik A. Rasmussen and John Turner|year=2003|publisher=Cambridge University Press|isbn=978-0-521-62430-5}}</ref> Those individual vortices can persist for more than a month.<ref name="pause"/>

[[Volcano|Volcanic]] eruptions in the [[tropics]] can lead to a stronger polar vortex during winter for as long as two years afterwards.<ref>{{cite journal |bibcode=2000RvGeo..38..191R |title=Volcanic eruptions and climate |last1=Robock |first1=Alan |volume=38 |year=2000 |pages=191–219 |journal=Reviews of Geophysics |doi=10.1029/1998RG000054 |issue=2|s2cid=1299888 |url=https://pdfs.semanticscholar.org/ce8e/392a97dbd25c7f20855547ec8be444416c4e.pdf |archive-url=https://web.archive.org/web/20200219140441/https://pdfs.semanticscholar.org/ce8e/392a97dbd25c7f20855547ec8be444416c4e.pdf |url-status=dead |archive-date=2020-02-19 }}</ref> The strength and position of the polar vortex shapes the flow pattern in a broad area about it. An index which is used in the [[northern hemisphere]] to gauge its magnitude is the [[Arctic oscillation]].<ref>Todd Mitchell (2004). [http://jisao.washington.edu/ao/ Arctic Oscillation (AO) time series, 1899 – June 2002] {{Webarchive|url=https://web.archive.org/web/20031212174712/http://jisao.washington.edu/ao/ |date=2003-12-12 }}. [[University of Washington]]. Retrieved on 2009-03-02.</ref>

When the Arctic vortex is at its strongest, there is a single vortex, but normally, the Arctic vortex is elongated in shape, with two cyclone centers, one over Baffin Island in [[Canada]] and the other over northeast [[Siberian High|Siberia]]. When the Arctic pattern is at its weakest, subtropic air masses can intrude poleward causing the Arctic air masses to move equatorward, as during the [[Winter 1985 Arctic outbreak]].<ref name="roanoke">Kevin Myatt (2005-01-17). [http://www.roanoke.com/weather/wb/16914 Cold enough for snow, and more's on the way] {{webarchive|url=https://archive.today/20130201105159/http://www.roanoke.com/weather/wb/16914 |date=2013-02-01 }}. ''[[Roanoke Times]]''. Retrieved on 2012-02-24.</ref> The [[Antarctic]] polar vortex is more pronounced and persistent than the [[Arctic]] one. In the Arctic the distribution of land masses at high latitudes in the Northern Hemisphere gives rise to [[Rossby wave]]s which contribute to the breakdown of the polar vortex, whereas in the Southern Hemisphere the vortex is less disturbed. The breakdown of the polar vortex is an extreme event known as a [[sudden stratospheric warming]], here the vortex completely breaks down and an associated warming of 30–50&nbsp;°C (54–90&nbsp;°F){{clarify|date=February 2019}} over a few days can occur.

The waxing and waning of the polar vortex is driven by the movement of mass and the transfer of heat in the polar region. In the autumn, the [[wikt:Special:Search/circumpolar|circumpolar]] winds increase in speed and the polar vortex rises into the [[stratosphere]]. The result is that the polar air forms a coherent rotating air mass: the polar vortex. As winter approaches, the vortex core cools, the winds decrease, and the vortex energy declines. Once late winter and early spring approach the vortex is at its weakest. As a result, during late winter, large fragments of the vortex air can be diverted into lower latitudes by stronger weather systems intruding from those latitudes. In the lowest level of the stratosphere, strong [[potential vorticity]] gradients remain, and the majority of that air remains confined within the polar air mass into December in the Southern Hemisphere and April in the Northern Hemisphere, well after the breakup of the vortex in the mid-stratosphere.<ref>{{cite journal |last1=Nash |first1=E |last2=Newman |first2=P |last3=Rosenfield |first3=J |last4=Schoeberl |first4=M |year=2012 |title=An objective determination of the polar vortex using Ertel's potential vorticity |journal=Journal of Geophysical Research |volume=101 |issue=D5 |pages=9471–9478 |doi=10.1029/96JD00066 |bibcode = 1996JGR...101.9471N |url=https://zenodo.org/record/1231378 }}</ref>

The breakup of the northern polar vortex occurs between mid March to mid May. This event signifies the transition from winter to spring, and has impacts on the [[hydrological cycle]], growing seasons of vegetation, and overall ecosystem productivity. The timing of the transition also influences changes in sea ice, ozone, air temperature, and cloudiness. Early and late polar breakup episodes have occurred, due to variations in the stratospheric flow structure and upward spreading of planetary waves from the troposphere.{{clarify|date=April 2016}} As a result of increased waves into the vortex, the vortex experiences more rapid warming than normal, resulting in an earlier breakup and spring. When the breakup comes early, it is characterized by{{Clarify|reason = by what?|date=November 2018}} with persistent of remnants of the vortex. When the breakup is late, the remnants dissipate rapidly. When the breakup is early, there is one warming period from late February to middle March. When the breakup is late, there are two warming periods, one January, and one in March. Zonal mean temperature, wind, and [[geopotential]] height exert varying deviations from their normal values before and after early breakups, while the deviations remain constant before and after late breakups. Scientists are connecting a delay in the Arctic vortex breakup with a reduction of planetary wave activities, few stratospheric sudden warming events, and depletion of ozone.<ref>{{cite journal |last1=Li |first1=L |last2=Li |first2=C |last3=Pan |first3=Y |date=2012 |title=On the differences and climate impacts of early and late stratospheric polar vortex breakup |journal=Advances in Atmospheric Sciences |volume=29 |issue=5 |pages=1119–1128 |doi=10.1007/s00376-012-1012-4|bibcode = 2012AdAtS..29.1119L |s2cid=123846176 }}</ref><ref>{{cite journal |last1=Wei |first1=K |last2=Chen |first2=W |last3=Huang |first3=R |date=2007 |title=Dynamical diagnosis of the breakup of the stratospheric polar vortex in the northern hemisphere| journal=Science in China Series D: Earth Sciences |volume=50 |issue=9 |pages=1369–1379 |doi=10.1007/s11430-007-0100-2 |bibcode=2007ScChD..50.1369W |s2cid=195309667 }}</ref>{{clarify|date=April 2016}}
[[File:Polarvortexjan211985.jpg|thumb|250px|Low pressure area over [[Quebec]], [[Maine]], and [[New Brunswick]], part of the northern polar vortex weakening, on the record-setting cold morning of January 21, 1985]]
[[Sudden stratospheric warming]] events are associated with weaker polar vortices. This warming of stratospheric air can reverse the circulation in the Arctic Polar Vortex from counter-clockwise to clockwise.<ref>{{cite journal |last1=Reichler| first=Tom| last2=Kim| first2=J |last3=Manzini |first3=E |last4=Kroger |first4=J|year=2012 |title=A stratospheric connection to Atlantic climate variability |journal=Nature Geoscience |volume=5 | issue=11|pages=783–787 |doi= 10.1038/ngeo1586|bibcode = 2012NatGe...5..783R }}</ref> These changes aloft force changes in the troposphere below.<ref>{{cite journal |last=Ripesi |first=Patrizio |year=2012 |title=The February 2010 Artcic Oscillation Index and its stratospheric connection|journal=Quarterly Journal of the Royal Meteorological Society|volume=138|issue=669 |pages=1961–1969|url=http://clima.meteoam.it/Articoli/Art14.pdf |doi=10.1002/qj.1935|bibcode = 2012QJRMS.138.1961R |s2cid=122729063 |display-authors=etal}}</ref> An example of an effect on the troposphere is the change in speed of the Atlantic Ocean circulation pattern. A soft spot just south of Greenland is where the initial step of [[downwelling]] occurs, nicknamed the "Achilles Heel of the North Atlantic". Small amounts of heating or cooling traveling from the polar vortex can trigger or delay [[downwelling]], altering the [[North Atlantic Current|Gulf Stream Current]] of the Atlantic, and the speed of other ocean currents. Since all other oceans depend on the Atlantic Ocean's movement of heat energy, climates across the planet can be dramatically affected. The weakening or strengthening of the polar vortex can alter the sea circulation more than a mile beneath the waves.<ref>{{cite journal |last1=Reichler |first1=Tom |last2=Kim |first2=J |last3=Manzini |first3=E |last4=Kroger |first4=J |year=2012 |title=A stratospheric connection to Atlantic climate variability |journal=Nature Geoscience |volume=5 |issue=11 |pages=783–787 |doi=10.1038/ngeo1586 |bibcode = 2012NatGe...5..783R }}</ref> Strengthening storm systems within the troposphere that cool the poles, intensify the polar vortex. [[La Niña]]–related climate anomalies significantly strengthen the polar vortex.<ref>{{cite journal |last1=Limpasuvan |first1=Varavut |last2=Hartmann |first2=Dennis L. |last3=Thompson |first3=David W.J. |last4=Jeev |first4=Kumar |last5=Yung |first5=Yuk L. |year=2005 |title=Stratosphere-troposphere evolution during polar vortex intensification |journal=Journal of Geophysical Research |volume=110 |issue=D24 |page=27 |doi=10.1029/2005JD006302 |url=http://yly-mac.gps.caltech.edu/ReprintsYLY/n173limpasuvan_2005.pdf |bibcode=2005JGRD..11024101L |citeseerx=10.1.1.526.9159 |access-date=2014-01-06 |archive-date=2017-08-12 |archive-url=https://web.archive.org/web/20170812193924/http://yly-mac.gps.caltech.edu/ReprintsYLY/n173limpasuvan_2005.pdf |url-status=dead }}</ref>  Intensification of the polar vortex produces changes in relative humidity as downward intrusions of dry, stratospheric air enter the vortex core. With a strengthening  of the vortex comes a longwave cooling due to a decrease in water vapor concentration near the vortex. The decreased water content is a result of a lower [[tropopause]] within the vortex, which places dry stratospheric air above moist tropospheric air.<ref>{{cite journal |last1=Cavallo |first1=S |last2=Hakim |first2=G.J. |year=2013 |title=Physical mechanisms of tropopause polar vortex intensity change |journal=Journal of the Atmospheric Sciences |volume=70 |issue=11 |pages=3359–3373 |doi=10.1175/JAS-D-13-088.1 |bibcode=2013JAtS...70.3359C |doi-access=free }}</ref> Instability is caused when the vortex tube, the line of concentrated [[vorticity]], is displaced. When this occurs, the vortex rings become more unstable and prone to shifting by planetary waves. The planetary wave activity in both hemispheres varies year-to-year, producing a corresponding response in the strength and temperature of the polar vortex.<ref>{{cite journal |last1=Hartmann |first1=D |last2=Schoeberl |first2=M |year=1991 |title=The dynamics of the stratospheric polar vortex and its relation to springtime ozone depletions |journal=Science |volume=251 |issue=4989 |pages=46–52 | doi = 10.1126/science.251.4989.46 |pmid=17778602|bibcode = 1991Sci...251...46S |s2cid=24664477 |url=http://pdfs.semanticscholar.org/b06e/6b492b632e72ea08f30a681500e8859bb4c7.pdf |archive-url=https://web.archive.org/web/20190302053349/http://pdfs.semanticscholar.org/b06e/6b492b632e72ea08f30a681500e8859bb4c7.pdf |url-status=dead |archive-date=2019-03-02 }}</ref> The number of waves around the perimeter of the vortex are related to the core size; as the vortex core  decreases, the number of waves increase.<ref>{{cite journal |last1=Widnall |first1=S |last2=Sullivan |first2=J |year=1973 |title=On the stability of vortex rings |journal=Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences |volume=332 |issue=1590 |pages=335–353 |doi=10.1098/rspa.1973.0029 |bibcode = 1973RSPSA.332..335W |s2cid=119959924 }}</ref>

The degree of the mixing of polar and mid-latitude air depends on the evolution and position of the [[polar night jet]]. In general, the mixing is less inside the vortex than outside. Mixing occurs with unstable planetary waves that are characteristic of the middle and upper stratosphere in winter. Prior to vortex breakdown, there is little transport of air out of the Arctic Polar Vortex due to strong barriers above 420&nbsp;km (261 miles). The polar night jet which exists below this, is weak in the early winter. As a result, it does not deviate any descending polar air, which then mixes with air in the mid-latitudes. In the late winter, air parcels do not descend as much, reducing mixing.<ref>{{cite journal |last1=Manney |first1=G |last2=Zurek |first2=R |last3=O'Neill |first3=A |last4=Swinbank |first4=R |year=1994 |title=On the motion of air through the stratospheric polar vortex |journal=Journal of the Atmospheric Sciences |doi=10.1175/1520-0469(1994)051<2973:otmoat>2.0.co;2 |volume =  51 |issue =20 | pages= 2973–2994 |bibcode = 1994JAtS...51.2973M |doi-access=free }}</ref> After the vortex is broken up, the ex-vortex air is dispersed into the middle latitudes within a month.<ref name=JGR2012/>

Sometimes, a mass of the polar vortex breaks off before the end of the final warming period. If large enough, the piece can move into Canada and the Midwestern, Central, Southern, and Northeastern United States. This diversion of the polar vortex can occur due to the displacement of the polar jet stream; for example, the significant northwestward direction of the polar jet stream in the western part of the United States during the winters of 2013–2014, and 2014–2015. This caused warm, dry conditions in the west, and cold, snowy conditions in the north-central and northeast.<ref>{{cite web|url=http://climatenexus.org/learn/planetary-systems/warm-west-cool-east-us-temperature-divide |title=The Warm West, Cool East U.S. Temperature Divide &#124; Climate Nexus |access-date=2015-11-26 |url-status=dead |archive-url=https://web.archive.org/web/20151207233627/http://climatenexus.org/learn/planetary-systems/warm-west-cool-east-us-temperature-divide |archive-date=2015-12-07 }}</ref> Occasionally, the high-pressure air mass, called the Greenland Block, can cause the polar vortex to divert to the south, rather than follow its normal path over the North Atlantic.<ref>{{cite web| last=Erdman |first=Jon |date=2014 |title=What's a Polar Vortex?: The Science Behind Arctic Outbreaks |website=wunderground |url=http://www.wunderground.com/news/polar-vortex-plunge-science-behind-arctic-cold-outbreaks-20140106 |
access-date= 25 February 2014}}</ref>

==Extreme weather==
A study in 2001 found that stratospheric circulation can have anomalous effects on weather regimes.<ref name="Baldwin 2001" /> In the same year, researchers found a statistical correlation between weak polar vortex and outbreaks of severe cold in the Northern Hemisphere.<ref name="Song 2001">{{cite web|title=Stratospheric Polar Vortex Influences Winter Cold|author=NASA|url=http://earthobservatory.nasa.gov/Newsroom/view.php?id=22082|archive-url=https://web.archive.org/web/20100316223817/http://earthobservatory.nasa.gov/Newsroom/view.php?id=22082|url-status=dead|archive-date=March 16, 2010|access-date=January 7, 2014|publisher=Earth Observatory|date=December 21, 2001}}</ref><ref name="Song 2004" /> In later years, scientists identified interactions with [[Arctic sea ice decline]], reduced snow cover, [[evapotranspiration]] patterns, [[North Atlantic oscillation|NAO]] anomalies or weather anomalies which are linked to the polar vortex and [[jet stream]] configuration.<ref name="Baldwin 2001">{{cite journal |doi=10.1126/science.1063315 |title=Stratospheric Harbingers of Anomalous Weather Regimes |year=2001 |last1=Baldwin |first1=M.P. |journal=Science |volume=294 |issue=5542 |pages=581–584 |pmid=11641495 |last2=Dunkerton |first2=TJ|bibcode = 2001Sci...294..581B |s2cid=34595603 }}</ref><ref name="Song 2004">{{cite journal |doi=10.1175/1520-0469(2004)061<1711:DMFSIO>2.0.CO;2 |year=2004 |volume=61 |pages=1711–1725 |title=Dynamical Mechanisms for Stratospheric Influences on the Troposphere |last1=Song |first1=Yucheng |last2=Robinson |first2=Walter A. |journal=Journal of the Atmospheric Sciences |issue=14|bibcode = 2004JAtS...61.1711S |doi-access=free }}</ref>

===Climate change===
{{excerpt|Jet stream#Longer-term climatic changes|paragraphs=1-8|file=yes}}

==Ozone depletion==
[[File:Srnhemozoneconcentration.gif|thumb|Southern Hemisphere ozone concentration, February 22, 2012]]

The chemistry of the Antarctic polar vortex has created severe [[ozone depletion]], although the effect has been weakening since the 2000s. It is expected to return to 1980 levels in about 2075. <ref>{{cite web |url=https://svs.gsfc.nasa.gov/30602 |title=The Antarctic Ozone Hole Will Recover|date=June 4, 2015|publisher=NASA |access-date=2017-08-05 }}</ref> The nitric acid in [[polar stratospheric cloud]]s reacts with [[chlorofluorocarbon]]s to form [[chlorine]], which [[catalysis|catalyzes]] the photochemical destruction of [[ozone]].<ref>{{cite book|pages=42–44|title=The Arctic and environmental change|author=J.A. Pyle|date=1997|publisher=CRC Press|isbn=978-90-5699-020-6|url=https://books.google.com/books?id=CSH2CU3eqNUC&pg=PA41}}</ref> Chlorine concentrations build up during the polar winter, and the consequent ozone destruction is greatest when the sunlight returns in spring.<ref>{{cite book|url=https://books.google.com/books?id=hXH-LO4iTZAC&pg=PA49|page=47|year=2010|title=Tracer-tracer Relations as a Tool for Research on Polar Ozone Loss|author=Rolf Müller|publisher=Forschungszentrum Jülich|isbn=978-3-89336-614-9}}</ref> These clouds can only form at temperatures below about {{Convert|-80|C|F}}.

Since there is greater air exchange between the Arctic and the mid-latitudes, ozone depletion at the north pole is much less severe than at the south.<ref>{{cite book|url=https://books.google.com/books?id=B93SSQrcAh4C&pg=PA34|page=34|title=Stratosphere troposphere interactions: an introduction|author=K. Mohanakuma|isbn=978-1-4020-8216-0|publisher=Springer|year=2008}}</ref> Accordingly, the seasonal reduction of ozone levels over the Arctic is usually characterized as an "ozone dent", whereas the more severe ozone depletion over the Antarctic is considered an "ozone hole". That said, chemical ozone destruction in the 2011 Arctic polar vortex attained, for the first time, a level clearly identifiable as an Arctic "[[ozone hole]]".<ref name="bbc">{{cite news|title=Arctic ozone loss at record level|url=https://www.bbc.co.uk/news/science-environment-15105747|publisher=BBC News Online|access-date=October 3, 2011|archive-url=https://web.archive.org/web/20111003182807/http://www.bbc.co.uk/news/science-environment-15105747|archive-date=October 3, 2011|url-status=live|date=October 2, 2011}}</ref>

==Outside Earth==
[[File:Mars cyclone.jpg|thumb|upright=1.2|[[Hubble Space Telescope]] view of the colossal polar cloud on Mars]]

Other astronomical bodies are also known to have polar vortices, including [[Venus]] (double vortex – that is, two polar vortices at a pole),<ref>{{Cite news|url=http://www.esa.int/Our_Activities/Space_Science/Venus_Express/Double_vortex_at_Venus_South_Pole_unveiled|title=Double vortex at Venus South Pole unveiled!|work=European Space Agency|access-date=2018-09-11|language=en-GB}}</ref> [[Mars]], [[Jupiter]], [[Saturn]], and Saturn's moon [[Titan (moon)|Titan]].

[[Saturn]]'s south pole is the only known hot polar vortex in the [[Solar System]].<ref>{{cite web|url = http://www.nasa.gov/vision/universe/solarsystem/saturn-020305.html|title = Saturn's Bull's-Eye Marks Its Hot Spot|year = 2005|publisher = NASA|access-date = January 8, 2014|archive-date = November 25, 2013|archive-url = https://web.archive.org/web/20131125121735/http://www.nasa.gov/vision/universe/solarsystem/saturn-020305.html|url-status = dead}}</ref>

==See also==
* {{Portal inline|Weather}}
* [[Polar amplification]]
* [[Saturn's hexagon]] – a persisting hexagonal cloud pattern around the north pole of Saturn
* [[Windward Performance Perlan II]] – will be used to study the northern polar vortex
* [[Polar front]]
* [[Cut-off low]]
* [[Sudden stratospheric warming]] 
{{Clear}}

==References==
{{Reflist|30em|refs=
<ref name=JGR2012>
  {{cite journal |last1=Waugh |first1=D |last2=Plumb |first2=R |last3=Elkins |first3=J |last4=Fahey |first4=D
  | last5=Boering |first5=K |last6=Dutton |first6=G |last7=Lait |first7=L |year=2012
  | title=Mixing of polar vortex air into middle latitudes as revealed by tracer-tracer scatterplots
  | journal=Journal of Geophysical Research: Atmospheres |volume=102 |issue=D11 |pages=13119–13134
  | doi=10.1029/96JD03715 |bibcode = 1997JGR...10213119W |doi-access=free }}</ref>
<ref name="pause">
  {{cite journal | title=Potential Vorticity Diagnosis of a Tropopause Polar Cyclone
  | author1=Cavallo, Steven M. | author2= Hakim, Gregory J. |date=April 2009|journal=Monthly Weather Review
  | volume=137|pages= 1358–1371|issue=4|doi=10.1175/2008MWR2670.1|bibcode = 2009MWRv..137.1358C | s2cid=16226331 |doi-access=free}}</ref>
}}

==Further reading==
* {{cite web|title=The science behind the polar vortex |url=https://www.noaa.gov/infographic/science-behind-polar-vortex |website=NOAA.gov (NASA)|date=29 Jan 2019|access-date=31 Jan 2019|language=en}}
* {{cite web|title=What Is a Polar Vortex? |url=https://scijinks.gov/polar-vortex/ |website=NOAA SciJinks.gov (NASA)|access-date=31 Jan 2019|language=en}}
* {{cite web|title=What is the Polar Vortex? |url=https://www.weather.gov/safety/cold-polar-vortex |website=US National Weather Service|access-date=31 Jan 2019|language=en}}
* {{cite journal |doi=10.1029/96JD00066 |title=An objective determination of the polar vortex using Ertel's potential vorticity |year=1996 |last1=Nash |first1=Eric R. |last2=Newman |first2=Paul A. |last3=Rosenfield |first3=Joan E. |last4=Schoeberl |first4=Mark R. |journal=Journal of Geophysical Research |volume=101 |issue=D5 |pages=9471–9478 |bibcode=1996JGR...101.9471N|url=https://zenodo.org/record/1231378 }}
* {{cite journal |doi=10.1175/1520-0469(1986)043<1319:TAOTSP>2.0.CO;2 |year=1986 |volume=43 |pages=1319–1339 |title=The Area of the Stratospheric Polar Vortex as a Diagnostic for Tracer Transport on an Isentropic Surface |last1=Butchart |first1=Neal |last2=Remsberg |first2=Ellis E. |journal=Journal of the Atmospheric Sciences |issue=13 |bibcode=1986JAtS...43.1319B|doi-access=free }}
* {{cite journal |doi=10.1029/91JD02168 |title=The structure of the polar vortex |year=1992 |last1=Schoeberl |first1=Mark R. |last2=Lait |first2=Leslie R. |last3=Newman |first3=Paul A. |last4=Rosenfield |first4=Joan E. |journal=Journal of Geophysical Research |volume=97 |issue=D8 |pages=7859–7882 |bibcode=1992JGR....97.7859S}}
* {{cite journal |doi=10.1029/97GL52832 |title=Meteorology of the polar vortex: Spring 1997 |year=1997 |last1=Coy |first1=Lawrence |last2=Nash |first2=Eric R. |last3=Newman |first3=Paul A. |journal=Geophysical Research Letters |volume=24 |issue=22 |pages=2693–2696 |bibcode=1997GeoRL..24.2693C|s2cid=128461145 }}
* {{cite journal |doi=10.1126/science.251.4989.46 |title=The Dynamics of the Stratospheric Polar Vortex and Its Relation to Springtime Ozone Depletions |year=1991 |last1=Schoeberl |first1=M.R. |last2=Hartmann |first2=D.L. |journal=Science |volume=251 |issue=4989 |pages=46–52 |pmid=17778602|bibcode = 1991Sci...251...46S }}

==External links==
{{Commons category|Polar vortex}}
*{{cite web |title=Current map of arctic winds and temperatures at the 10 hPa level|url=https://earth.nullschool.net/#current/wind/isobaric/10hPa/overlay=temp/orthographic=00.000,90.000/loc=00.000,90.000}}
*{{cite web |title=Current map of arctic winds and temperatures at the 70 hPa level|url=https://earth.nullschool.net/#current/wind/isobaric/70hPa/overlay=temp/orthographic=00.000,90.000/loc=00.000,90.000}}
*{{cite web |title=Current map of arctic winds and temperatures at the 250 hPa level|url=https://earth.nullschool.net/#current/wind/isobaric/250hPa/overlay=temp/orthographic=00.000,90.000/loc=00.000,90.000}}
*{{cite web |title=Current map of arctic winds and temperatures at the 500 hPa level|url=https://earth.nullschool.net/#current/wind/isobaric/500hPa/overlay=temp/orthographic=00.000,90.000/loc=00.000,90.000}}
*{{cite web |title=Current map of antarctic winds and temperatures at the 10 hPa level|url=https://earth.nullschool.net/#current/wind/isobaric/10hPa/overlay=temp/orthographic=180.000,-89.999/loc=180.000,-89.999}}
*{{cite web |title=Current map of antarctic winds and temperatures at the 70 hPa level|url=https://earth.nullschool.net/#current/wind/isobaric/70hPa/overlay=temp/orthographic=180.000,-89.999/loc=180.000,-89.999}}
*{{cite web |title=Current map of antarctic winds and temperatures at the 250 hPa level|url=https://earth.nullschool.net/#current/wind/isobaric/250hPa/overlay=temp/orthographic=180.000,-89.999/loc=180.000,-89.999}}
*{{cite web |title=Current map of antarctic winds and temperatures at the 500 hPa level|url=https://earth.nullschool.net/#current/wind/isobaric/500hPa/overlay=temp/orthographic=180.000,-89.999/loc=180.000,-89.999}}

{{Cyclones}}
{{Authority control}}

[[Category:Atmospheric dynamics]]
[[Category:Regional climate effects]]
[[Category:Polar regions of the Earth]]
[[Category:Vortices]]