Editing Polar vortex (section)

===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>