Editing Polar vortex (section)

==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>