Polar stratospheric cloud
1077335
225895570
2008-07-15T22:20:21Z
Tomaxer
3686472
/* Types of PSC */ I don't think that there will ever be an article supercooled ternary solution :-)
{{Infobox Cloud
| name = Polar Stratospheric Cloud
| image location = Arctic_stratospheric_cloud.jpg
| image name = Arctic stratospheric cloud (nacreous clouds)
| abbreviation = PSC
| genus=
| species=
| variety=
| altitude_m = 15,000–25,000
| altitude_ft = 50,000–80,000
| level = other
| appearance = Glowing brightly with vivid [[Iridescent Cloud|iridescent]] colours
| precipitation = no
}}
'''Polar stratospheric clouds''' ('''PSCs'''), also known as '''nacreous clouds''', are [[clouds]] in the winter polar [[stratosphere]] at altitudes of 15,000–25,000 metres (50,000–80,000 ft). They are implicated in the formation of [[ozone hole]]s;
<ref>
[[United States Environmental Protection Agency]] — see [http://www.epa.gov/ozone/science/hole/whyant.html#psc]
</ref>
their 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]] and [[chlorine]] cycles in a way which increases [[ozone]] destruction.
<ref>
[[World Meteorological Organization]] ''[http://www.wmo.int/disasters/DRR_related_Publications/Ozone/WMO_Scientific_Assessment_of_Ozone_Depletion_(2002)_e.pdf Scientific Assessment of Ozone Depletion (2002)]'', particularly section 3.2.2 (pages 3.21, i.e. 195 of the PDF file, and following).
</ref>
==Formation==
The stratosphere is very dry; unlike the [[troposphere]], it rarely allows clouds to form. In the extreme cold of the polar winter, however, stratospheric clouds of different types may form, which are classified according to their [[physical state]] and [[chemical composition]].
Due to their high altitude and the curvature of the surface of the [[Earth]], these clouds will receive sunlight from below the horizon and reflect it to the ground, shining brightly well before [[dawn]] or after [[dusk]].
PSCs form at very low temperatures, below −78 °C. These temperatures can occur in the lower [[stratosphere]] in polar winter. In the [[Antarctic]], temperatures below −88 °C frequently cause type II PSCs. Such low temperatures are rarer in the [[Arctic]]. In the Northern [[Northern Hemisphere|hemisphere]], the generation of [[lee waves]] by mountains may locally cool the lower stratosphere and lead to the formation of PSCs.
[[Image:Polar_stratospheric_cloud_type_2.jpg|left|thumb|A type 2 (water) PSC]]
== Types of PSC ==
PSCs are classified into three types Ia, Ib and II according to their [[chemical composition]].
* Type I clouds contain [[nitric acid]] and [[water]].
* Type Ia clouds consist of crystals formed from [[nitric acid]] and [[water]].
* Type Ib cloud droplets additionally contain [[sulfuric acid]] and are present in the form of [[Supercooling|supercooled]] ternary solution.
* Type II clouds consist of [[ice|water ice]] only.
<br /><br />
[[Image:Perlemorskyer Polar stratospheric cloud.jpg|thumb|280px|Polar stratospheric cloud seen over Norway. <small>''Foto:Mathias Midbøe''</small>]]
== See also ==
* [[Iridescent Cloud]]
* [[Noctilucent cloud]]s
* [[Ozone depletion]]
* [[Aurora (astronomy)]]
*[[Circumhorizontal arc]]
==References==
*[http://web.archive.org/web/20060902171924/http://www.iac.ethz.ch/research/chemistry/polar_stratospheric_clouds/ ETH PSC page]
*http://www.meteoros.de/psc/psce.htm
<references/>
== External links ==
{{commons|Polar stratospheric cloud}}
===Research===
*[http://www.atoptics.co.uk/highsky/nacr1.htm Nacreous Clouds] at atoptics.co.uk
*[http://www.awi.de/en/research/research_divisions/climate_science/atmospheric_circulations/research_themes/aerosol/polar_stratospheric_clouds/ Polar Stratospheric Clouds Above Spitsbergen] at [[Alfred Wegener Institute for Polar and Marine Research|Alfred Wegener Institute]]
===News reports===
*http://www.smh.com.au/news/science/extreme-weather-makes-rare-cloud/2006/08/01/1154198117951.html
*http://news.yahoo.com/s/ap/20060801/ap_on_sc/antarctica_clouds_4
*http://www.cnn.com/2006/TECH/science/08/01/antarctica.clouds.ap/index.html
*http://www.dailymail.co.uk/pages/live/articles/news/worldnews.html?in_article_id=398592&in_page_id=1811
{{Cloud types}}
[[Category:Cloud types]]
[[Category:Ozone depletion]]
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[[ru:Перламутровые облака]]
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