Editing Cirrus cloud (section)

== Cloud properties ==
[[File:Cirrus fibratus and Cirrocumulus.jpg|thumb|alt=Long, thin, straight cirrus against a blue sky on the left merging to cirrocumulus on the right|Cirrus clouds merging to cirrocumulus clouds]]

Scientists have studied the properties of cirrus using several different methods. [[Lidar]] (laser-based [[radar]]) gives highly accurate information on the cloud's altitude, length, and width. Balloon-carried [[hygrometer]]s{{efn|A hygrometer is a device used to measure humidity.}} measure 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]] 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> [[NASA]]'s [[Moderate-Resolution Imaging Spectroradiometer]] 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)|access-date=29 January 2011|page=2, 3, & 5|archive-date=3 April 2019|archive-url=https://web.archive.org/web/20190403015955/https://www.nrlmry.navy.mil/sat_training/nexsat/cirrus/NexSat_Cirrus.pdf}}</ref> Visual observations from aircraft or the ground provide additional information about cirrus clouds.<ref name="D&R-972"/> Particle Analysis by Laser [[Mass Spectrometry]] (PALMS){{efn|The PALMS instrument utilizes an [[Ultraviolet light|ultraviolet]] laser to vaporize aerosol particles<ref>{{cite web|url=https://airbornescience.nasa.gov/instrument/PALMS|title=Particle Analysis by Laser Mass Spectrometry (PALMS)|access-date=18 March 2022|website=NASA Airborne Science Program|publisher=National Aeronautics and Space Administration|archive-date=3 May 2022|archive-url=https://web.archive.org/web/20220503184131/https://airbornescience.nasa.gov/instrument/PALMS|url-status=live}}</ref> in a vacuum. The ionized particles are analyzed with a mass spectrometer to determine mass and composition.<ref>{{cite web|url=https://csl.noaa.gov/groups/csl2/instruments/palms/instrument.html|title=Aerosol Properties & Processes: Instruments: PALMS|access-date=18 March 2022|website=NOAA Chemical Sciences Laboratory|publisher=National Oceanic and Atmospheric Administration|archive-date=3 May 2022|archive-url=https://web.archive.org/web/20220503184130/https://csl.noaa.gov/groups/csl2/instruments/palms/instrument.html|url-status=live}}</ref>}} is used to identify the type of nucleation seeds that spawned the ice crystals in a cirrus cloud.<ref name="cirrus-origins" />

Cirrus clouds have an average ice crystal concentration of 300,000 ice crystals per 10 [[cubic metre|cubic meters]] (270,000 ice crystals per 10 [[cubic yard]]s). The concentration ranges from as low as 1 ice crystal per 10 cubic meters to as high as 100 million ice crystals per 10 cubic meters (just under 1 ice crystal per 10 cubic yards to 77 million ice crystals per 10 cubic yards), a difference of eight [[orders of magnitude]]. The size of each ice crystal is typically 0.25&nbsp;millimeters,<ref name="D&R-977">{{harvnb|Dowling|Radke|1990|p=977}}</ref> but they range from as short as 0.01&nbsp;millimeters up to several millimeters.<ref name="McGraw-1"/> The ice crystals in contrails can be much smaller than those in naturally-occurring cirrus cloud, being around 0.001&nbsp;millimeters to 0.1&nbsp;millimeters in length.<ref name="McGraw-2">{{harvnb|McGraw-Hill Editorial Staff|2005|p=2}}</ref>

In addition to forming in different sizes, the ice crystals in cirrus clouds can crystallize in different shapes: 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]] (the amount by which the [[relative humidity]] exceeds 100%). Cirrus in temperate regions typically have the various ice crystal shapes separated by type. The columns and plates concentrate near the top of the cloud, whereas the rosettes and conglomerations concentrate near the base. In the northern [[Arctic]] region, cirrus clouds 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 columns which are much longer than normal.<ref name="McGraw-1"/>

Cirrus clouds are usually colder than {{convert|-20|C|F|abbr=on}}.<ref name="McGraw-1">{{harvnb|McGraw-Hill Editorial Staff|2005|p=1}}</ref> At temperatures above {{convert|-68|C|F}}, most cirrus clouds have relative humidities of roughly 100% (that is they are saturated).{{sfn|Krämer|Schiller|Afchine|Bauer|2009|p=3516}} Cirrus can supersaturate, with relative humidities over ice that can exceed 200%.{{sfn|Krämer|Schiller|Afchine|Bauer|2009|p=3505}}{{sfn|Krämer|Schiller|Afchine|Bauer|2009|p=3516}} Below {{convert|-68|C|F}} there are more of both undersaturated and supersaturated cirrus clouds.{{sfn|Krämer|Schiller|Afchine|Bauer|2009|p=3517}} The more supersaturated clouds are probably young cirrus.{{sfn|Krämer|Schiller|Afchine|Bauer|2009|p=3516}}