Editing Jet stream (section)

==Other upper-level jets==

===Polar night jet===
The polar-night jet stream forms mainly during the winter months when the nights are much longer – hence the name referencing [[polar night]]s – in their respective hemispheres at around 60° latitude. The polar night jet moves at a greater height (about {{convert|80000|ft|m|order=flip}}) than it does during the summer.<ref>{{Cite web| title=Jet Streams around the World| url=http://www.bbc.co.uk/weather/features/understanding/jetstreams_world.shtml| publisher=BBC| access-date=26 September 2009| archive-date=13 February 2009| archive-url=https://web.archive.org/web/20090213061211/http://www.bbc.co.uk/weather/features/understanding/jetstreams_world.shtml| url-status=dead}}</ref> During these dark months the air high over the poles becomes much colder than the air over the Equator. This difference in temperature gives rise to extreme air pressure differences in the stratosphere which, when combined with the Coriolis effect, create the polar night jets, that race eastward at an altitude of about {{convert|30|mi|km|order=flip}}.<ref>{{Cite web | title=The Jet Stream | url=http://www.gi.alaska.edu/ScienceForum/ASF6/640.html | last=Gedney | first=Larry | publisher=University of Alaska Fairbanks | year=1983 | access-date=13 December 2018 | archive-url=https://web.archive.org/web/20100115013949/http://www.gi.alaska.edu/ScienceForum/ASF6/640.html | archive-date=15 January 2010 | url-status=dead}}</ref> <!-- Note to other editors: Observe that "80,000 feet" (BBC source) and "30 miles" (Alaska source) are incompatible. Any ideas? --> The [[polar vortex]] is circled by the polar night jet. The warmer air can only move along the edge of the polar vortex, but not enter it. Within the vortex, the cold polar air becomes increasingly cold, due to a lack of warmer air from lower latitudes as well as a lack of energy from the Sun entering during the polar night.<ref>{{Cite web|url=http://www.stat.osu.edu/~sses/collab_ozone_split_background.php |title=2002 Ozone-Hole Splitting – Background |publisher=Ohio State University |url-status=dead |archive-url=https://web.archive.org/web/20100621115326/http://www.stat.osu.edu/~sses/collab_ozone_split_background.php |archive-date=21 June 2010 }}</ref>