Editing Cirrus cloud (section)

{{Short description|Genus of atmospheric cloud}}
{{Use dmy dates|date=March 2022}}
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[[File:CirrusField-color.jpg|thumb|upright=1.6|alt=A picture of a bright blue sky with many different types of white cirrus clouds. The clouds are over a grassy field with a line of trees in the distance.|Sky containing different types of cirrus clouds]]
'''Cirrus''' ([[list of cloud types|cloud classification]] symbol: '''Ci''') is a [[Cloud#Levels and genera|genus]] of high [[cloud]] made of ice [[crystals]]. Cirrus clouds typically appear delicate and wispy with white strands. In the Earth's atmosphere, cirrus are usually formed when warm, dry air rises, causing [[water vapor]] [[Deposition (phase transition)|deposition]] onto mineral dust and metallic particles at high altitudes. Globally, they form anywhere between {{convert|4000|and|20000|m|ft|abbr=off|sp=us}} above [[sea level]], with the higher elevations usually in the [[tropics]] and the lower elevations in more [[Polar regions of Earth|polar regions]].

Cirrus clouds can form from the tops of [[cumulonimbus cloud|thunderstorms]] and [[tropical cyclone]]s and sometimes predict the arrival of [[precipitation|rain]] or storms. Although they are a sign that rain and maybe storms are on the way, cirrus themselves drop no more than [[virga|falling streak]]s of ice crystals. These crystals dissipate, melt, and evaporate as they fall through warmer and drier air and never reach ground. The word ''cirrus'' comes from the [[Latin]] prefix ''cirro-'', meaning "tendril" or "curl".<ref name="cloud-class">{{cite web|url=http://www.crh.noaa.gov/lmk/?n=cloud_classification|title=Cloud Classification|access-date=2 January 2014|publisher=National Weather Service}}</ref> Cirrus clouds warm the earth, potentially contributing to [[climate change]]. A warming earth will likely produce more cirrus clouds, potentially resulting in a [[climate change feedback|self-reinforcing loop]].

[[Optical phenomena]], such as [[sun dog]]s and [[halo (optical phenomenon)|halos]], can be produced by light interacting with ice crystals in cirrus clouds. There are two other high-level cirrus-like clouds called [[cirrostratus]] and [[cirrocumulus]]. Cirrostratus looks like a sheet of cloud, whereas cirrocumulus looks like a pattern of small cloud tufts. Unlike cirrus and cirrostratus, cirrocumulus clouds contain droplets of [[supercooling|supercooled]] (below [[freezing point]]) water.

Cirrus clouds form in the atmospheres of [[Atmosphere of Mars|Mars]], [[Atmosphere of Jupiter|Jupiter]], [[Saturn#Atmosphere|Saturn]], [[Atmosphere of Uranus|Uranus]], and [[Neptune#Atmosphere|Neptune]]; and on [[Atmosphere of Titan|Titan]], one of Saturn's larger moons. Some of these [[Extraterrestrial atmosphere|extraterrestrial]] cirrus clouds are made of [[ammonia]] or [[methane]], much like water ice in cirrus on Earth. Some [[interstellar cloud]]s, made of grains of [[cosmic dust|dust]] smaller than a thousandth of a millimeter, are also called ''cirrus''.