Editing Polar stratospheric cloud (section)

==Types==
[[File:Polar stratospheric cloud type 2.jpg|thumb|right|A lenticular type II (water) PSC showing iridescence]]

PSCs are classified into two main types, each of which consists of several subtypes.

*Type I clouds have a generally stratiform appearance resembling cirrostratus or haze.<ref name="PSC">{{cite web |editor=World Meteorological Organization |title=Nitric acid and water PSC, International Cloud Atlas |year=2017 |url=https://cloudatlas.wmo.int/nitric-acid-and-water-polar-stratospheric-clouds.html|access-date=3 April 2019}}</ref> They are sometimes sub-classified according to their [[chemical composition]] which can be measured using [[LIDAR]]. The technique also determines the height and ambient temperature of the cloud.<ref name=wegener /> They contain water, [[nitric acid]] and/or [[sulfuric acid]] and are a source of polar [[ozone depletion]].<ref>{{cite web |url=http://www.atoptics.co.uk/highsky/psc1.htm|title=Nacreous and Polar Stratospheric Clouds |website=atoptics.co.uk |date=16 September 2023 |access-date=24 December 2023}}</ref> The effects on [[ozone depletion]] arise because they support chemical reactions that produce active [[chlorine]] which catalyzes [[ozone]] destruction, and also because they remove gaseous [[nitric acid]], perturbing [[nitrogen cycle|nitrogen]] and chlorine cycles in a way which increases ozone depletion.<ref>{{cite web |publisher=[[World Meteorological Organization]] |url=http://www.wmo.int/disasters/DRR_related_Publications/Ozone/WMO_Scientific_Assessment_of_Ozone_Depletion_(2002)_e.pdf |title=Scientific Assessment of Ozone Depletion |year=2002 |access-date=2006-10-28 |archive-date=2020-03-13 |archive-url=https://web.archive.org/web/20200313150114/https://public.wmo.int/en/search?search_api_views_fulltext=disasters&sort_by=search_api_relevance%2FDRR_related_Publications%2FOzone%2FWMO_Scientific_Assessment_of_Ozone_Depletion_%282002%29_e.pdf |url-status=dead }}particularly section 3.2.2 (pages 3.21, i.e. 195 of the PDF file, and following).</ref>
**Type Ia clouds consist of large, aspherical particles, consisting of nitric acid trihydrate (NAT).<ref name=wegener />
**Type Ib clouds contain small, spherical particles (non-depolarising), of a liquid [[supercooled]] ternary solution (STS) of sulfuric acid, nitric acid, and water.<ref name=wegener />
**Type Ic clouds consist of [[Metastability|metastable]] water-rich nitric acid in a solid phase.<ref>{{cite web|publisher=[[Journal of Geophysical Research]]|url=http://www.agu.org/journals/jd/v101/iD04/96JD00062/96JD00062.pdf|title=The presence of metastable HNO<sub>3</sub>/H<sub>2</sub>O solid phases in the stratosphere inferred from ER 2 data|access-date=2012-08-17|archive-date=2020-01-26|archive-url=https://web.archive.org/web/20200126223114/http://www.agu.org/journals/jd/v101/iD04/96JD00062/96JD00062.pdf|url-status=dead}}</ref>

*Type II clouds, which are very rarely observed in the Arctic, have cirriform and lenticular sub-types <ref name="nacreous">{{cite web |editor=World Meteorological Organization |title=Nacreous PSC, International Cloud Atlas |year=2017 |url=https://cloudatlas.wmo.int/nacreous-clouds.html|access-date=3 April 2019}}</ref> and consist of [[ice|water ice]] only.<ref name=wegener>{{cite web|last=Maturilli|first=Maturilli|title=Polar Stratospheric Clouds Above Spitsbergen|url=http://www.awi.de/en/research/research_divisions/climate_science/atmospheric_circulations/research_themes/aerosol/polar_stratospheric_clouds/|publisher=[[Alfred Wegener Institute for Polar and Marine Research]]|url-status=dead|archive-url=https://web.archive.org/web/20070824200937/http://www.awi.de/en/research/research_divisions/climate_science/atmospheric_circulations/research_themes/aerosol/polar_stratospheric_clouds/|archive-date=2007-08-24}}</ref>

[[File:Polar Stratospheric Cloud type I above Cirrus.jpg|thumb|right|upright=2|A stratiform type I PSC (white cloud above the orange tropospheric clouds), showing fine horizontal structures in the veil]]

Only Type II clouds are necessarily nacreous<ref name=AAD>{{cite web|publisher=[[Australian Antarctic Division]]|url=http://www.antarctica.gov.au/about-antarctica/fact-files/atmosphere/polar-stratospheric-clouds/observations|archive-url=https://web.archive.org/web/20110602123302/http://www.antarctica.gov.au/about-antarctica/fact-files/atmosphere/polar-stratospheric-clouds/observations|url-status=dead|archive-date=June 2, 2011|title=Polar stratospheric clouds / Observations}}</ref> whereas Type I clouds can be iridescent under certain conditions, just as [[Cloud iridescence|any other cloud]].  The [[World Meteorological Organization]] no longer uses the alpha-numeric nomenclature seen in this article, and distinguishes only between super-cooled stratiform acid-water PSCs and cirriform-lenticular water ice nacreous PSCs.<ref name="Polar-stratospheric">{{cite web |editor=World Meteorological Organization |title=Upper atmospheric clouds, International Cloud Atlas |year=2017 |url=https://cloudatlas.wmo.int/upper-atmospheric-clouds.html|access-date=31 July 2017}}</ref>