Examine individual changes

'{{Use dmy dates|date=May 2016}} [[File:CirrusField-color.jpg|thumb|right|300px|alt=A photograph showing many types of cirrus clouds all jumbled together floating above a plain|A sky filled with many types of cirrus clouds accompanied by cirrocumulus upper centre and upper right]] '''Cirrus''' ([[List of cloud types|cloud classification]] symbol: '''Ci''') is a genus of [[Cloud|atmospheric cloud]] generally characterized by thin, wispy strands, giving the type its name from the [[Latin]] word ''cirrus'', meaning a ringlet or curling lock of hair.<ref name="richmond">{{cite web|title=Cirrus Clouds |url=http://chalk.richmond.edu/education/projects/webunits/weather/cirrus.html |work=Clouds |publisher=University of Richmond |accessdate=29 January 2011 |deadurl=yes |archiveurl=https://web.archive.org/web/20090824085243/http://chalk.richmond.edu/education/projects/webunits/weather/cirrus.html |archivedate=24 August 2009 }}</ref><ref name="cloud-classification">{{cite web|last=Funk|first=Ted|title=Cloud Classifications and Characteristics|url=http://www.crh.noaa.gov/lmk/soo/docu/cloudchart.pdf|work=The Science Corner|publisher=[[National Oceanic and Atmospheric Administration]]|accessdate=30 January 2011|format=PDF|page=1}}</ref> This cloud can form anywhere between 16,500 and 45,000 feet in the sky. The strands of cloud sometimes appear in tufts of a distinctive form referred to by the common name of "mares' tails".<ref name="usatoday">{{cite news|url=http://www.usatoday.com/weather/wcirrus.htm|title=USA Today: Cirrus Clouds|last=Palmer|first=Chad|accessdate=13 September 2008| work=USA Today | date=16 October 2005}}</ref> On planet Earth, cirrus generally appears white or light gray in color. It forms when water vapor undergoes [[Deposition (phase transition)|deposition]] at altitudes above {{convert|18,000|ft|m|disp=flip|abbr=on}} in temperate regions and above {{convert|21,000|ft|m|disp=flip|abbr=on}} in tropical regions. It also forms from the outflow of [[tropical cyclone]]s or the [[anvil cloud|anvils]] of [[cumulonimbus cloud]]. Since cirrus clouds arrive in advance of the [[frontal system]] or [[tropical cyclone]], it indicates that weather conditions may soon deteriorate. While it indicates the arrival of [[precipitation (meteorology)|precipitation]] (rain), cirrus clouds only produce [[virga|fall streak]]s (falling ice crystals that evaporate before landing on the ground). [[Jet stream]]-powered cirrus can grow long enough to stretch across continents while remaining only a few kilometers deep.<ref name="D&R-974">{{harvnb|Dowling|Radke|1990|p=974}}</ref> When visible light interacts with the ice crystals in cirrus cloud, it produces [[optical phenomena]] such as [[sun dog]]s and [[Halo (optical phenomenon)|haloes]]. Cirrus is known to raise the temperature of the air beneath the main cloud layer by an average of 10&nbsp;°C (18&nbsp;°F). When the individual filaments become so extensive that they are virtually indistinguishable from one another, they form a sheet of high cloud called [[Cirrostratus cloud|cirrostratus]]. Convection at high altitudes can produce another high-based genus called [[Cirrocumulus cloud|cirrocumulus]], a pattern of small cloud tufts that contain droplets of [[supercooled]] water. Cirrus clouds form on other planets, including [[Mars]], [[Jupiter]], [[Saturn]], [[Uranus]], and possibly [[Neptune]]. They have even been seen on [[Titan (moon)|Titan]], one of Saturn's moons. Some of these extraterrestrial cirrus clouds are composed of [[ammonia]] or [[methane]] ice rather than water ice. The term ''cirrus'' is also used for certain [[interstellar cloud]]s composed of sub-[[Micrometer (unit)|micrometer]]-sized dust grains. ==Description== [[File:Cirrus fibratus and Cirrocumulus.jpg|thumb|left|alt=Long, thin, straight cirrus against a blue sky on the left merging to cirrocumulus on the right|Cirrus clouds merging to cirrocumulus clouds]] Cirrus cloud ranges in thickness from {{convert|100|m|ft|abbr=on|sigfig=2}} to {{convert|8000|m|ft|abbr=on}}, with an average thickness of {{convert|1500|m|ft|abbr=on}}. There are, on average, 30&nbsp;[[ice crystals]] per [[liter]] (96&nbsp;ice crystals per [[gallon]]), but this ranges from one ice crystal per 10,000 liters (3.7&nbsp;ice crystals per 10,000 gallons) to 10,000 ice crystals per liter (37,000 ice crystals per gallon), a difference of eight [[orders of magnitude]]. The length of each of these ice crystals is usually 0.25&nbsp;millimeters long,<ref name="D&R-977">{{harvnb|Dowling|Radke|1990|p=977}}</ref> but they range from as short as 0.01&nbsp;millimeters or as long as several millimeters.<ref name="McGraw-1"/> The ice crystals in [[contrail]]s are much smaller than those in naturally occurring cirrus cloud, as they are around 0.001&nbsp;millimeters to 0.1&nbsp;millimeters in length.<ref name="McGraw-2"/> Cirrus can vary in temperature from {{convert|-20|C|F|abbr=on|lk=on}} to {{convert|-30|C|F|abbr=on}}.<ref name="McGraw-1">{{harvnb|McGraw-Hill Editorial Staff|2005|p=1}}</ref> The ice crystals in cirrus clouds have different shapes in addition to different sizes. Some shapes include solid columns, hollow columns, plates, rosettes, and conglomerations of the various other types. The shape of the ice crystals is determined by the air temperature, atmospheric pressure, and ice [[supersaturation]]. Cirrus in temperate regions typically have the shapes segregated by type: the columns and plates tend to be at the top of the cloud, whereas the rosettes and conglomerations tend to be near the base.<ref name="McGraw-1"/> In the northern [[Arctic]] region, cirrus tend to be composed of only the columns, plates, and conglomerations, and these crystals tend to be at least four times larger than the minimum size. In [[Antarctica]], cirrus are usually composed of only the columns, and these columns are much longer than normal.<ref name="McGraw-1"/> [[File:Cirrus o zachodzie.jpg|thumb|right|alt=A picture of contorted cirrus cloud shining red in the sunset. Fall streaks (like long thin streamers) descend from the clouds.|Fall streaks in a cirrus cloud]] Scientists have studied the characteristics of cirrus using several different methods. One, [[Light Detection and Ranging]] (LiDAR), gives highly accurate information on the cloud's altitude, length, and width. Balloon-carried [[hygrometer]]s give information on the humidity of the cirrus cloud but are not accurate enough to measure the depth of the cloud. Radar units give information on the altitudes and thicknesses of cirrus clouds.<ref name="D&R-971">{{harvnb|Dowling|Radke|1990|p=971}}</ref> Another data source is satellite measurements from the [[Stratospheric Aerosol and Gas Experiment]] (SAGE) program. These satellites measure where [[infrared radiation]] is absorbed in the atmosphere, and if it is absorbed at cirrus altitudes, then it is assumed that there are cirrus clouds in that ___location.<ref name="D&R-972">{{harvnb|Dowling|Radke|1990|p=972}}</ref> The United States [[National Aeronautics and Space Administration]]'s (NASA) [[Moderate-Resolution Imaging Spectroradiometer|MODerate resolution Imaging Spectroradiometer]] (MODIS) also gives information on the cirrus cloud cover by measuring reflected infrared radiation of various specific frequencies during the day. During the night, it determines cirrus cover by detecting the Earth's infrared emissions. The cloud reflects this radiation back to the ground, thus enabling satellites to see the "shadow" it casts into space.<ref name=cirrus-detection>{{cite web|title=Cirrus Cloud Detection|url=http://www.nrlmry.navy.mil/sat_training/nexsat/cirrus/NexSat_Cirrus.pdf|work=Satellite Product Tutorials|publisher=NASA (NexSat)|accessdate=29 January 2011|format=PDF|pages=2, 3, & 5}}</ref> Visual observations from aircraft or the ground provide additional information about cirrus clouds.<ref name="D&R-972"/> [[File:Long Cirrus fibratus.jpg|thumb|left|alt=Cirrus fibratus clouds pictured against the sky|''Cirrus fibratus'' clouds]] Based upon data taken from the United States using these methods, cirrus cloud cover was found to vary [[Diurnal cycle|diurnally]] and seasonally. The researchers found that in the summer, at noon, the cover is the lowest, with an average of 23% of the United States' land area covered by cirrus. Around midnight, the cloud cover increases to around 28%. In winter, the cirrus cloud cover did not vary appreciably from day to night. These percentages include clear days and nights, as well as days and nights with other cloud types, as lack of cirrus cloud cover. When these clouds are present, the typical coverage ranges from 30% to 50%.<ref name="D&R-974"/> Based on satellite data, cirrus covers an average of 20% to 25% of the Earth's surface. In the tropical regions, this cloud covers around 70% of the region's surface area.<ref name="McGraw-1"/> Cirrus clouds often produce hair-like filaments—similar to the [[virga]] produced in liquid–water clouds—called fall streaks, and they are made of heavier ice crystals that fall from the cloud. The sizes and shapes of fall streaks are determined by the [[wind shear]].<ref name="Illinois-University">{{cite web|title=Cirrus Clouds: Thin and Wispy|url=http://ww2010.atmos.uiuc.edu/%28Gh%29/guides/mtr/cld/cldtyp/hgh/crs.rxml|work=Cloud Types|publisher=Department of Atmospheric Sciences at University of Illinois|accessdate=29 January 2011}}</ref> [[File:Cirrus clouds2.jpg|thumb|right|alt=Hooked cirrus clouds showing the cirrus uncinus subform.|The ''cirrus uncinus'' subform of cirrus clouds]] Cirrus comes in four distinct species; Cirrus ''castellanus'', ''fibratus'', ''spissatus'', and ''uncinus''; which are each divided into four varieties: ''intortus'', ''vertebratus'', ''radiatus'', and ''duplicatus''.<ref>{{cite web|url=http://www.clouds-online.com/cloud_atlas/cirrus/cirrus.htm |title=Cirrus – Clouds Online|accessdate=20 March 2012}}</ref> ''Cirrus castellanus'' is a species that has cumuliform tops caused by high-altitude convection rising up from the main cloud body. ''Cirrus fibratus'' looks striated and is the most common cirrus species. ''Cirrus uncinus'' clouds are hooked and are the form that is usually called ''mare's tails''. Of the varieties, ''Cirrus intortus'' has an extremely contorted shape, and ''cirrus radiatus'' has large, radial bands of cirrus clouds that stretch across the sky. [[Kelvin–Helmholtz instability|Kelvin–Helmholtz waves]] are a form of cirrus intortus that has been twisted into loops by vertical wind shear.<ref name="audubon-446">{{harvnb|Audubon|2000|p=446}}</ref> ==Formation== Cirrus clouds are formed when water vapor undergoes deposition at high altitudes where the [[atmospheric pressure]] ranges from 600&nbsp;[[Millibars|mbar]] at {{convert|4000|m|ft|abbr=on}} above sea level to 200&nbsp;mbar at {{convert|12000|m|ft|abbr=on}} above sea level.<ref name="D&R-973">{{harvnb|Dowling|Radke|1990|p=973}}</ref> These conditions commonly occur at the leading edge of a [[warm front]].<ref name="audubon-447"/> Because humidity is low at such high altitudes, this genus-type tends to be very thin.<ref name="usatoday"/> ===Cyclones=== [[File:Hurricane Isabel 10 sept 2003 1640Z.jpg|thumb|right|alt=A picture showing the vast shield of cirrus clouds accompanying Hurricane Isabel in 2003.|A vast shield of cirrus clouds accompanying the west side of [[Hurricane Isabel]]]] Cirrus forms from tropical cyclones, and is commonly seen fanning out from the [[eye (cyclone)|eyewalls]] of [[hurricane]]s. A large shield of cirrus and [[cirrostratus cloud|cirrostratus]] typically accompanies the high altitude [[outflow (meteorology)|outflow]] of hurricanes or [[typhoon]]s,<ref name="cirrus-detection"/> and these can make the underlying [[rain band]]s—and sometimes even the eye—difficult to detect in satellite photographs.<ref>{{cite web|url=http://www.nrlmry.navy.mil/sat_training/tropical_cyclones/ssmi/composite/index.html|title=Tropical Cyclone SSMI – Composite Tutorial|publisher=[[United States Navy]]|accessdate=18 February 2011}}</ref> ===Thunderstorms=== [[File:Cirren von Cumulonimbus-Amboss und Cu&Sc.JPG|thumb|left|alt=A picture showing the cirrus clouds lancing out from the anvil of the thunderstorm. Picture taken just before the lower mass of the cumulonimbus cloud went over the photographer.|Cirrus in an anvil cloud]] [[Thunderstorm]]s can form dense cirrus at their tops. As the cumulonimbus cloud in a thunderstorm grows vertically, the liquid water droplets freeze when the air temperature reaches the [[freezing point]].<ref name="lydolph-122">{{harvnb|Lydolph|1985|p=122}}</ref> The [[anvil cloud]] takes its shape because the [[temperature inversion]] at the tropopause prevents the warm, moist air forming the thunderstorm from rising any higher, thus creating the flat top.<ref name="G&N-212">{{harvnb|Grenci|Nese|2001|p=212}}</ref> In the tropics, these thunderstorms occasionally produce copious amounts of cirrus from their anvils.<ref>{{cite web|title=Computer-simulated Thunderstorms with Ice Clouds Reveal Insights for Next-generation Computer Models |url=http://www.pnl.gov/science/highlights/highlight.asp?id=709 |work=Atmospheric Sciences & Global Change Division Research Highlights |publisher=Pacific Northwest National Laboratory |accessdate=30 January 2011 |page=42 |date=December 2009 |archiveurl=https://web.archive.org/web/20110514115603/http://www.pnl.gov/science/highlights/highlight.asp?id=709 |archivedate=14 May 2011 |deadurl=yes |df=dmy }}</ref> High-altitude winds commonly push this dense mat out into an anvil shape that stretches [[downwind]] as much as several kilometers.<ref name="G&N-212"/> Individual cirrus cloud formations can be the remnants of anvil clouds formed by thunderstorms. In the dissipating stage of a cumulonimbus cloud, when the normal column rising up to the anvil has evaporated or dissipated, the mat of cirrus in the anvil is all that is left.<ref name="G&N-213">{{harvnb|Grenci|Nese|2001|p=213}}</ref> ===Contrails=== [[Contrail]]s are a manmade type of cirrus cloud formed when water vapor from the exhaust of a jet engine condenses on particles, which come from either the surrounding air or the exhaust itself, and freezes, leaving behind a visible trail. The exhaust can also trigger the formation of cirrus by providing [[ice nuclei]] when there is an insufficient naturally-occurring supply in the atmosphere.<ref name="McGraw-2"/> One of the [[Environmental impact of aviation|environmental impacts of aviation]] is that persistent contrails can form into large mats of cirrus,<ref name="NASA-cirrus">{{cite web|url=http://www.nasa.gov/home/hqnews/2004/apr/HQ_04140_clouds_climate.html|publisher=[[National Aeronautics and Space Administration]]|title=Clouds Caused By Aircraft Exhaust May Warm The U.S. Climate|date=27 April 2004|first1=Gretchen|last1=Cook-Anderson|first2=Chris|last2=Rink|first3=Julia|last3=Cole|accessdate=24 June 2011}}</ref> and increased air traffic has been implicated as one possible cause of the increasing frequency and amount of cirrus in Earth's atmosphere.<ref name="NASA-cirrus"/><ref name="Minnis-1671">{{harvnb|Minnis|Ayers|Palikonda|Phan|2004|p=1671}}</ref> {{clear}} == Subforms == === Species === '''Cirrus Fibratus''' clouds appear as thin and fibrous looking. Noticeably, they are the most common type of cirrus cloud. They might indicate windy weather, since they are mostly formed by [[wind shear]] on higher altitudes. '''Cirrus Uncinus''' clouds appear as thin and fibrous like, except that they always have a hook or curl on the tip. '''Cirrus Spissatus''' clouds are the highest clouds of the main cloud genera. They may form in the higher [[tropopause]] or even at the lower [[stratosphere]]. They are dense and opaque, not allowing the light of the sun or moon to pass through. They are more common on the anvils of [[cumulonimbus]] clouds. '''Cirrus Floccus''' is derived from [[Latin]], which means "lock of wool" or cirrus with ragged bases. They are not to be confused with cirrocumulus floccus since they are larger than [[cirrocumulus]] and mostly are isolated. A precipitation-based supplementary feature [[virga]] is mostly visible, which makes it easier to distinguish the difference between cirrocumulus floccus and cirrus floccus. '''Cirrus Castellanus''' is derived from [[Latin]], which means "castle" or round turrets. They indicate that [[atmospheric instability]] is occurring on the higher altitudes of the [[troposphere]]. They appear as tall clouds that originate from a flat base. === Opacity-based Varieties === Cirrus clouds are translucent and so have no opacity-based varieties; only one species is opaque, which is cirrus spissatus. === Pattern-based Varieties === '''Cirrus Intortus''' clouds is derived from [[Latin]] which means "twisted", or "wound". These clouds appear twisted, or simply, intorted. '''Cirrus Vertebratus''' clouds, resembling the appearance of bones as hinted by the word "vertebratus". They look more like fish bones, with fibrous lines that originate from one which resembles the appearance of fish bones. '''Cirrus Radiatus''' clouds appear as parallel lines that seem to originate from one point and can stretch for hundreds of miles, and they move parallel to the wind shear. ==Use in forecasting== {{See also|Weather forecasting|Tropical cyclone track forecasting}} [[File:Highcloudsymbols.gif|thumb|300px|High cloud weather map symbols.]] Random, isolated cirrus do not have any particular significance.<ref name="audubon-447"/> A large number of cirrus clouds can be a sign of an approaching [[Weather front|frontal system]] or upper air disturbance. This signals a change in weather in the near future, which usually becomes stormier.<ref name="WeatherBattan">{{cite book|last=Battan|first=Louis|authorlink= Louis J. Battan |title=Weather|publisher=Prentice Hall|___location=Englewood Cliffs, New Jersey|year=1974|series=Foundations of Earth Science Series|page=74|isbn=0-13-947762-4}}</ref> If the cloud is a [[cirrus castellanus cloud|cirrus castellanus]], there might be instability at the high altitude level.<ref name="audubon-447">{{harvnb|Audubon|2000|p=447}}</ref> When the clouds deepen and spread, especially when they are of the ''cirrus radiatus'' variety or ''cirrus fibratus'' species, this usually indicates an approaching weather front. If it is a warm front, the cirrus clouds spread out into cirrostratus, which then thicken and lower into [[Altocumulus cloud|altocumulus]] and [[Altostratus cloud|altostratus]]. The next set of clouds are the rain-bearing [[nimbostratus cloud]]s.<ref name="cloud-classification"/><ref name="audubon-447"/><ref name="whiteman-84">{{harvnb|Whiteman|2000|p=84}}</ref> When cirrus clouds precede a [[cold front]], [[squall line]] or [[multicellular thunderstorm]], it is because they are blown off the anvil, and the next to arrive are the cumulonimbus clouds.<ref name="whiteman-84"/> Kelvin-Helmholtz waves indicate extreme wind shear at high levels.<ref name="audubon-447"/> Within the tropics, 36&nbsp;hours prior to the center passage of a tropical cyclone, a veil of white cirrus clouds approaches from the direction of the cyclone.<ref>{{cite web|author=Central Pacific Hurricane Center|date=23 July 2006|url=http://www.prh.noaa.gov/cphc/pages/FAQ/Observations.php|title=Tropical Cyclone Observations|accessdate=5 May 2008|publisher=[[National Oceanic and Atmospheric Administration]]|authorlink=Central Pacific Hurricane Center}}</ref> In the mid to late 19th century, forecasters used these cirrus veils to predict the arrival of hurricanes. In the early 1870s the president of Belén College in [[Havana, Cuba]], Father [[Benito Vines|Benito Viñes]], developed the first hurricane forecasting system, and he mainly used the motion of these clouds in formulating his predictions.<ref>{{harvnb|Sheets|1990|p=190}}</ref> He would observe the clouds hourly from 4:00 am to 10:00 pm. After accumulating enough information, Viñes began accurately predicting the paths of hurricanes, and he eventually summarized his observations in his book, ''Apuntes Relativos a los Huracanes de las Antilles''.<ref>{{cite news|url=http://www.cubanet.org/CNews/y98/mar98/13e5.htm |publisher=Cable News Network, Inc |title=Father Hurricane |accessdate=22 February 2011 |date=11 March 1998 |archiveurl=http://www.webcitation.org/60P871oh4?url=http://www.cubanet.org/CNews/y98/mar98/13e5.htm |archivedate=24 July 2011 |deadurl=yes |df=dmy }}</ref> ==Effects on climate== Cirrus clouds cover up to 25% of the Earth and have a net heating effect.<ref name="Nucleation">{{cite journal|doi=10.1098/rsta.2002.1141|author=Franks F.|title=Nucleation of ice and its management in ecosystems|journal=Philosophical Transactions of the Royal Society A|volume=361|issue=1804|year=2003|pages=557–574|format=PDF|url =http://rsta.royalsocietypublishing.org/content/361/1804/557.long|pmid=12662454|bibcode=2003RSPTA.361..557F}}</ref> When they are thin and translucent, the clouds efficiently absorb outgoing [[infrared]] radiation while only marginally reflecting the incoming sunlight.<ref name="stephens-1742">{{harvnb|Stephens|Tsay|Stackhouse|Flatau|1990|p=1742}}</ref> When cirrus clouds are {{convert|100|m|ft|abbr=on}} thick, they reflect only around 9% of the incoming sunlight, but they prevent almost 50% of the outgoing infrared radiation from escaping, thus raising the temperature of the atmosphere beneath the clouds by an average of 10&nbsp;°C (18&nbsp;°F)<ref name="liou-1191">{{harvnb|Liou|1986|p=1191}}</ref>—a process known as the [[greenhouse effect]].<ref name="earthobs-global-warming">{{cite web|url=http://earthobservatory.nasa.gov/Features/GlobalWarming/|publisher=National Aeronautics and Space Administration|title=Global Warming: Feature Articles|accessdate=16 October 2012|work=Earth Observatory}}</ref> Averaged worldwide, cloud formation results in a temperature loss of 5&nbsp;°C (9&nbsp;°F) at the earth's surface, mainly the result of [[stratocumulus cloud]]s.<ref name="cloud-heating">{{cite web|url=http://isccp.giss.nasa.gov/role.html|title=Cloud Climatology|work=International Satellite Cloud Climatology Program|publisher=National Aeronautics and Space Administration|accessdate=12 July 2011}}</ref> [[File:Cirrus Clounds.jpg|thumb|left|alt=Fine type of Cirrus Clouds|''Cirrus fibratus'' clouds]] As a result of their warming effects when relatively thin, cirrus clouds have been implicated as a potential partial cause of [[global warming]].<ref name="stephens-1742"/> Scientists have speculated that global warming could cause high thin cloud cover to increase, thereby increasing temperatures and humidity. This, in turn, would increase the cirrus cloud cover, effectively creating a [[positive feedback]] circuit. A prediction of this hypothesis is that the cirrus would move higher as the temperatures rose, increasing the volume of air underneath the clouds and the amount of infrared radiation reflected back down to earth.<ref name="McGraw-2">{{harvnb|McGraw-Hill Editorial Staff|2005|p=2}}</ref> In addition, the hypothesis suggests that the increase in temperature would tend to increase the size of the ice crystals in the cirrus cloud, possibly causing the reflection of solar radiation and the reflection of the Earth's infrared radiation to balance out.<ref name="McGraw-2"/><ref name="cloud-heating"/> A similar hypothesis put forth by [[Richard Lindzen]] is the [[iris hypothesis]] in which an increase in tropical [[sea surface temperatures]] results in less cirrus clouds and thus more infrared radiation emitted to space.<ref>{{cite journal |url=http://eaps.mit.edu/faculty/lindzen/adinfriris.pdf |author1=Lindzen, R.S. |author2=M.-D. Chou |author3=A.Y. Hou |last-author-amp=yes |year=2001 |title=Does the Earth have an adaptive infrared iris? |journal=Bull. Amer. Meteor. Soc. |volume=82 |pages=417–432 |doi=10.1175/1520-0477(2001)082<0417:DTEHAA>2.3.CO;2 |bibcode=2001BAMS...82..417L |issue=3}}</ref> ==Optical phenomena== [[File:CircumhorizonArcIdaho.jpg|thumb|right|alt=A circumhorizontal arc projected onto a sheet of striated cirrus clouds seen through a hole in lower-level cumulus clouds.|A [[circumhorizontal arc]] over Idaho, June 2006]] Cirrus clouds, like [[Cirrostratus|cirrostratus clouds]], can produce several optical effects, such as [[Halo (optical phenomenon)|halos]] around the sun and moon. Halos are caused by interaction of the light with hexagonal ice crystals present in the clouds, which, depending on their shape and orientation, can result in a wide variety of white and colored rings, arcs and spots in the sky. Common [[halo (optical phenomenon)|halo]] varieties are the [[22° halo]], [[sun dogs]], the [[circumzenithal arc]] and the [[circumhorizontal arc]].<ref name="McGraw-1"/><ref name="natlgeo-rainbow">{{cite news|last=Gilman|first=Victoria|title=Photo in the News: Rare "Rainbow" Spotted Over Idaho|url=http://news.nationalgeographic.com/news/2006/06/060619-rainbow-fire.html|accessdate=30 January 2011|newspaper=National Geographic News|date=19 June 2006}}</ref><ref name=ucsb>{{cite web|title=Fire Rainbows|url=http://www.geog.ucsb.edu/events/department-news/618/fire-rainbows/|work=News & Events|publisher=University of the City of Santa Barbara Department of Geology|accessdate=31 January 2011|date=29 August 2009}}</ref> Halos produced by cirrus clouds tend to be more pronounced and colorful than those caused by [[cirrostratus]]. More rarely, cirrus clouds are capable of producing [[Glory (optical phenomenon)|glories]], more commonly associated with liquid water-based clouds such as [[Stratus cloud|stratus]]. A glory is a set of concentric, faintly-colored glowing rings that appear around the shadow of the observer, and are best observed from a high viewpoint or from a plane.<ref name="glory-weather.gov">{{cite web|url=http://www.weather.gov.hk/education/edu06nature/ele_glory1106_e.htm|title=The Mysterious Glory|publisher=The Hong Kong Observatory|accessdate=27 June 2011}}</ref> Cirrus clouds only form glories when the constituent ice crystals are [[wikt:aspherical|aspherical]], and researchers suggest that the ice crystals must be between 0.009&nbsp;millimeters and 0.015&nbsp;millimeters in length.<ref name="glory-1433">{{harvnb|Sassen|Arnott|Barnett|Aulenbach|1998|p=1433}}</ref> {{clear}} ==Relation to other clouds== {{see also|List of cloud types}} [[File:Wolkenstockwerke.png|thumb|right|alt=A diagram showing clouds at various heights|The heights of various cloud genera including high, middle, low, and vertical]] Cirrus clouds are one of three different genera of high-étage (high-level) clouds. High-étage clouds form at {{convert|16500|ft|m|disp=flip|abbr=on}} and above in temperate regions. The other two genera, [[cirrocumulus cloud|cirrocumulus]] and cirrostratus, are also high clouds. In the intermediate range, from {{convert|6500|ft|m|disp=flip|abbr=on}} to {{convert|23000|ft|m|disp=flip|abbr=on}} in temperate regions, are the mid-étage clouds. They comprise two or three genera depending on the system of height classification being used: [[altostratus cloud|altostratus]], [[altocumulus cloud|altocumulus]], and, according to [[World Meteorological Organization|WMO]] classification, [[nimbostratus cloud|nimbostratus]]. These clouds are formed from ice crystals, supercooled water droplets, or liquid water droplets.<ref name="nws-jetstream">{{cite web|url=http://www.srh.noaa.gov/srh/jetstream/synoptic/clouds_max.htm|archiveurl=https://web.archive.org/web/20060510131751/http://www.srh.noaa.gov/srh/jetstream/synoptic/clouds_max.htm|archivedate=10 May 2006|title=Cloud Classifications|publisher=National Weather Service|work=JetStream|accessdate=18 June 2011}}</ref> Low-étage clouds form at less than {{convert|6500|ft|m|disp=flip|abbr=on}}. The two genera that are strictly low-étage are [[stratus cloud|stratus]], and [[stratocumulus cloud|stratocumulus]]. These clouds are composed of water droplets, except during winter when they are formed of supercooled waterdroplets or ice crystals if the temperature at cloud level is below freezing. Two additional genera usually form in the low altitude range, but may be based at higher levels under conditions of very low humidity. They comprise the genera [[cumulus cloud|cumulus]], and [[cumulonimbus cloud|cumulonimbus]], which along with nimbostratus, are often classified separately as clouds of vertical development, especially when their tops are high enough to be composed of super-cooled water droplets or ice crystals.<ref name="Plymouth State Meteorology">{{cite web | url=http://vortex.plymouth.edu/clouds.html/ | title=Plymouth State Meteorology Program Cloud Boutique | author = Jim Koermer | year = 2011 | accessdate=2 April 2012| publisher=[[Plymouth State University]]}}</ref> The altitudes of high-étage clouds like cirrus vary considerably with latitude. In the polar regions, they are at their lowest, with a minimum altitude of only {{convert|10000|ft|m|disp=flip|abbr=on}} to a maximum of {{convert|25000|ft|m|disp=flip|abbr=on}}. In tropical regions, they are at their highest, ranging in altitude from about {{convert|20000|ft|m|disp=flip|abbr=on}} to around {{convert|60000|ft|m|disp=flip|abbr=on}}. In temperate regions, they range in altitude from {{convert|16500|ft|m|disp=flip|abbr=on}} to {{convert|45000|ft|m|disp=flip|abbr=on}}—a variation in contrast to low-étage clouds, which do not appreciably change altitude with latitude.<ref name="nws-jetstream"/> ===Summary of high cloud genera=== [[File:Sunset Solar Halo at Keys View of Joshua Tree National Park.jpg|thumb|right|alt=A picture of a solar halo shown as the fun sets|A solar halo]] There are three main genera in the family of high clouds: cirrus, cirrocumulus, and cirrostratus.<ref name="H&H-340">{{harvnb|Hubbard|Hubbard|2000|p=340}}</ref> Cirrostratus clouds commonly produce halos because they are composed almost entirely of ice crystals.<ref name="glossary-cirriform">{{cite web|url=http://www.weather.com/glossary/c.html|title=Weather Glossary – C|work=Weather Glossary|publisher=The Weather Channel|accessdate=12 February 2011}}</ref> Cirrocumulus and cirrostratus are sometimes informally referred to as "[[cirriform cloud]]s" because of their frequent association with cirrus. They are given the prefix "cirro-", but this refers more to their altitude range than their physical structure. Cirrocumulus in its pure form is actually a high cumuliform genus, and cirrostratus is stratiform, like altostratus and lower based sheet clouds. ====Cirrocumulus==== [[File:Cirrocumulus in Hong Kong.jpg|thumb|left|alt=A large field of cirrocumulus clouds in a blue sky, beginning to merge near the upper left.|A large field of cirrocumulus clouds]] {{Main article|Cirrocumulus cloud}} Cirrocumulus clouds form in sheets or patches<ref name="YDN-364">{{harvnb|Miyazaki|Yoshida|Dobashi|Nishita|2001|p=364}}</ref> and do not cast shadows. They commonly appear in regular, rippling patterns<ref name="H&H-340"/> or in rows of clouds with clear areas between.<ref name="cloud-classification"/> Cirrocumulus are, like other members of the cumuliform category, formed via [[convection|convective]] processes.<ref name="parungo-251">{{harvnb|Parungo|1995|p=251}}</ref> Significant growth of these patches indicates high-altitude instability and can signal the approach of poorer weather.<ref name="common-clouds"/><ref name="audubon-448"/> The ice crystals in the bottoms of cirrocumulus clouds tend to be in the form of hexagonal cylinders. They are not solid, but instead tend to have stepped funnels coming in from the ends. Towards the top of the cloud, these crystals have a tendency to clump together.<ref name="parungo-252">{{harvnb|Parungo|1995|p=252}}</ref> These clouds do not last long, and they tend to change into cirrus because as the water vapor continues to deposit on the ice crystals, they eventually begin to fall, destroying the upward convection. The cloud then dissipates into cirrus.<ref name="parungo-254">{{harvnb|Parungo|1995|p=254}}</ref> Cirrocumulus clouds come in four species: ''stratiformis'', ''lenticularis'', ''castellanus'', and ''floccus''.<ref name="common-clouds">{{cite web|title=Common Cloud Names, Shapes, and Altitudes|format=PDF|publisher=Georgia Institute of Technology|url=http://nenes.eas.gatech.edu/Cloud/Clouds.pdf|accessdate=12 February 2011|pages=2, 10–13}}</ref> They are [[iridescence|iridescent]] when the constituent supercooled water droplets are all about the same size.<ref name="audubon-448">{{harvnb|Audubon|2000|p=448}}</ref> ====Cirrostratus==== [[File:Close Cirrostratus stratiformis.JPG|thumb|right|alt=Milky-white cirrostratus clouds cause the sky to appear lighter and have a milky tint.|A cirrostratus cloud]] {{Main article|Cirrostratus cloud}} Cirrostratus clouds can appear as a milky sheen in the sky<ref name="common-clouds"/> or as a striated sheet.<ref name="H&H-340"/> They are sometimes similar to altostratus and are distinguishable from the latter because the sun or moon is always clearly visible through transparent cirrostratus, in contrast to altostratus which tends to be opaque or translucent.<ref name="Day-56">{{harvnb|Day|2005|p=56}}</ref> Cirrostratus come in two species, ''fibratus'' and ''nebulosus''.<ref name="common-clouds"/> The ice crystals in these clouds vary depending upon the height in the cloud. Towards the bottom, at temperatures of around {{convert|-35|C|F}} to {{convert|-45|C|F}}, the crystals tend to be long, solid, hexagonal columns. Towards the top of the cloud, at temperatures of around {{convert|-47|C|F}} to {{convert|-52|C|F}}, the predominant crystal types are thick, hexagonal plates and short, solid, hexagonal columns.<ref name="parungo-254"/><ref name="parungo-256">{{harvnb|Parungo|1995|p=256}}</ref> These clouds commonly produce halos, and sometimes the halo is the only indication that such clouds are present.<ref name="ahrens-120">{{harvnb|Ahrens|2006|p=120}}</ref> They are formed by warm, moist air being lifted slowly to a very high altitude.<ref name="hamilton-24">{{harvnb|Hamilton|p=24}}</ref> When a warm front approaches, cirrostratus clouds become thicker and descend forming altostratus clouds,<ref name="cloud-classification"/> and rain usually begins 12 to 24 hours later.<ref name="ahrens-120"/> ==Extraterrestrial== [[File:Cirrus clouds on mars.jpg|thumb|left|500px|alt=A composite black-and-white photograph showing cirrus clouds over the surface of Mars.|Cirrus clouds on Mars]] Cirrus clouds have been observed on several other planets. On 18 September 2008, the Martian Lander ''[[Phoenix Lander|Phoenix]]'' took a [[time-lapse]] photograph of a group of cirrus clouds moving across the Martian sky using LiDAR.<ref name="NASA-photo">{{cite web|url=http://www.nasa.gov/mission_pages/phoenix/images/press/16145-animated.html|title=Clouds Move Across Mars Horizon|date=19 September 2008|accessdate=15 April 2011|publisher=[[National Aeronautics and Space Administration]]|work=Phoenix Photographs}}</ref> Near the end of its mission, the Phoenix Lander detected more thin clouds close to the north pole of Mars. Over the course of several days, they thickened, lowered, and eventually began snowing. The total precipitation was only a few thousandths of a millimeter. James Whiteway from [[York University]] concluded that "precipitation is a component of the [Martian] [[hydrologic cycle]]."<ref name="MSNBC-Mars-snow">{{cite news|url=http://www.msnbc.msn.com/id/31713000/ns/technology_and_science-space/ |title=How Martian Clouds Create Snowfall |first=Andrea |last=Thompson |newspaper=Space.com |date=2 July 2009 |publisher=[[MSNBC]] |accessdate=15 April 2011 |archiveurl=http://www.webcitation.org/60P7lZptN?url=http://www.msnbc.msn.com/id/31713000/ns/technology_and_science-space/ |archivedate=24 July 2011 |deadurl=yes |df=dmy }}</ref> These clouds formed during the Martian night in two layers, one around {{convert|4000|m|ft|abbr=on}} above ground and the other at surface level. They lasted through early morning before being burned away by the sun. The crystals in these clouds were formed at a temperature of {{convert|-65|C|F}}, and they were shaped roughly like ellipsoids 0.127&nbsp;millimeters long and 0.042&nbsp;millimeters wide.<ref>{{harvnb|Whiteway|Komguem|Dickinson|Cook|2009|pp=68–70}}</ref> On Jupiter, cirrus clouds are composed of [[ammonia]]. When Jupiter's [[South Equatorial Belt]] disappeared, one hypothesis put forward by Glenn Orten was that a large quantity of ammonia cirrus clouds had formed above it, hiding it from view.<ref>{{cite web|url=http://science.nasa.gov/science-news/science-at-nasa/2010/20may_loststripe/|title=Big Mystery: Jupiter Loses a Stripe|date=20 May 2010|last=Phillips|first=Tony|publisher=[[National Aeronautics and Space Administration]]|work=Nasa Headline News – 2010|accessdate=15 April 2011}}</ref> NASA's [[Cassini probe]] detected these clouds on Saturn<ref>{{harvnb|Dougherty|Esposito|2009|page=118}}</ref> and thin water-ice cirrus on Saturn's moon [[Titan (moon)|Titan]].<ref>{{cite web|url=http://www.nasa.gov/mission_pages/cassini/whycassini/titan-clouds_prt.htm|title=Surprise Hidden in Titan's Smog: Cirrus-Like Clouds|publisher=[[National Aeronautics and Space Administration]]|date=3 February 2011|work=Mission News|accessdate=16 April 2011}}</ref> Cirrus clouds composed of [[methane]] ice exist on Uranus.<ref>{{cite web|url=http://www2.scholastic.com/browse/article.jsp?id=4871 |title=Uranus |publisher=Scholastic |accessdate=16 April 2011 |archiveurl=https://web.archive.org/web/20110902053831/http://www2.scholastic.com/browse/article.jsp?id=4871 |archivedate=2 September 2011 |deadurl=yes |df=dmy }}</ref> On Neptune, thin wispy clouds which could possibly be cirrus have been detected over the [[Great Dark Spot]]. As on Uranus, these are probably methane crystals.<ref>{{harvnb|Ahrens|2006|page=12}}</ref> {{clear}} [[Infrared cirrus|Interstellar cirrus clouds]] are composed of tiny dust grains smaller than a [[Micrometer (unit)|micrometer]] and are therefore not true clouds of this genus which are composed of ice crystals or other frozen liquids.<ref name="bluebook_c1">{{cite journal |author=Planck Science Team|title=Planck: The Scientific Programme (''Blue Book'') |version=ESA-SCI (2005)-1. Version 2 |pages=123–124 |format=PDF |publisher=European Space Agency |url=http://www.rssd.esa.int/SA/PLANCK/docs/Bluebook-ESA-SCI%282005%291_V2.pdf |year=2005|accessdate=8 July 2009}}</ref> They range from a few [[light year]]s to dozens of light years across. While they are not technically cirrus clouds, the dust clouds are referred to as "cirrus" because of their similarity to the clouds on Earth. They also emit infrared radiation, similar to the way cirrus clouds on Earth reflect heat being radiated out into space.<ref>{{harvnb|Koupelis|2010|page=368}}</ref> ==See also== * [[Cirrus cloud thinning]] ==Sources== '''Footnotes''' {{Reflist|35em}} '''Bibliography''' {{refbegin}} *{{cite book|title=Meteorology Today: An Introduction to Weather, Climate, and the Environment|first=C. Donald|last=Ahrens|url=https://books.google.com/books?id=SpGfKb23Y9QC&lpg=PA120|oclc=693475796|publisher=Brooks Cole|date=February 2006|isbn=978-0-495-01162-0|edition=8|ref=CITEREFAhrens2006}} <!-- Ahrens --> *{{cite book|title=National Audubon Society Field Guide to Weather|year=2000|publisher=Alfred A. 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Jr. |author4= Flatau, Piotr J. |title=The Relevance of the Microphysical and Radiative Properties of Cirrus Clouds to Climate and Climatic Feedback|journal=Journal of Atmospheric Sciences|date=July 1990|volume=47|issue=14|bibcode=1990JAtS...47.1742S|ref=CITEREFStephensTsayStackhouseFlatau1990|pages=1742}} <!-- Stephens --> *{{cite book|url=https://books.google.com/?id=Mz_7qLK5hQcC&lpg=PA84|title=Mountain Meteorology: Fundamentals and Applications|last=Whiteman|first=Charles David|date=May 2000|isbn=978-0-19-513271-7|edition=1|publisher=Oxford University Press, USA|oclc=41002851|ref=CITEREFWhiteman2000}} <!-- Whiteman --> *{{cite journal|author1=Whiteway, J. A. |author2=Komguem, L. |author3=Dickinson, C. |author4=Cook, C. |author5=Illnicki, M. |author6=Seabrook, J. |author7=Popovici, V. |author8=Duck, T. J. |author9=Davy, R. |author10=Taylor, P. A. |author11=Pathak, J. |author12=Fisher, D. |author13=Carswell, A. I. |author14=Daly, M. |author15=Hipkin, V. |author16=Zent, A. P. |author17=Hecht, M. H. |author18=Wood, S. E. |author19=Tamppari, L. K. |author20=Renno, N. |author21=Moores, J. E. |author22=Lemmon, M. T. |author23=Daerden, F. |author24=Smith, P. H. |title=Mars Water-Ice Clouds and Precipitation|journal=Science Magazine|volume=325|doi=10.1126/science.1172344|date=3 July 2009|bibcode=2009Sci...325...68W|issue=5936|ref=CITEREFWhitewayKomguemDickinsonCook2009|pmid=19574386|pages=68–70}} <!-- Whiteway et al. --> {{refend}} ==External links== {{commons category|Cirrus clouds}} *[http://www.clouds-online.com A cloud atlas with many photos and description of the different cloud genera] *[http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cld/cldtyp/hgh/crs.rxml UIUC.edu's online guide to meteorology] *[http://nephology.eu/cirrus International Cloud Atlas – Cirrus] {{Cloud types}} {{featured article}} [[Category:Cirrus]]'