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&ndash;25,000 metres (50,000&ndash;80,000 ft). They are implicated in the formation of [[ozone hole]]s; <ref> [[United States Environmental Protection Agency]] &mdash; 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 &minus;78 °C. These temperatures can occur in the lower [[stratosphere]] in polar winter. In the [[Antarctic]], temperatures below &minus;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]] [[de:Polare Stratosphärenwolken]] [[fr:Nuage nacré]] [[nl:Parelmoerwolk]] [[ja:真珠母雲]] [[no:Perlemorskyer]] [[nn:Perlemorskyer]] [[pl:Polarne chmury stratosferyczne]] [[ru:Перламутровые облака]] [[fi:Helmiäispilvi]] [[sv:Pärlemormoln]]