Editing Cirrus cloud (section)

== Relation to other clouds ==
{{See also|List of cloud types}}
[[File:Cloud types en.svg|thumb|upright=1.6|alt=A diagram showing clouds at various heights|Heights of various cloud genera including high-, mid-, and low-level clouds]]
Cirrus clouds are one of three different genera of high-level clouds, all of which are given the prefix "cirro-". The other two genera are [[cirrocumulus cloud|cirrocumulus]] and cirrostratus. High-level clouds usually form above {{convert|20000|ft|m|order=flip|abbr=on}}.<ref name="cloud-classification" /><ref name="wmo-cloud-classification">{{cite web|url=https://public-old.wmo.int/en/WorldMetDay2017/classifying-clouds|archive-url=https://web.archive.org/web/20231218182558/https://public-old.wmo.int/en/WorldMetDay2017/classifying-clouds|archive-date=18 December 2023|access-date=14 March 2022|title=Classifying clouds|date=18 January 2017|publisher=[[World Meteorological Organization]]}}</ref><ref name="H&H-340">{{harvnb|Hubbard|2000|p=340}}</ref> Cirrocumulus and cirrostratus are sometimes informally referred to as ''cirriform clouds'' because of their frequent association with cirrus.<ref>{{cite web|url=https://glossary.ametsoc.org/wiki/Cirriform|title=Cirriform – Glossary of Meteorology|access-date=23 February 2022|publisher=American Meteorological Society|archive-date=23 February 2022|archive-url=https://web.archive.org/web/20220223170359/https://glossary.ametsoc.org/wiki/Cirriform|url-status=live}}</ref>

In the intermediate range, from {{convert|6500|to|20000|ft|m|order=flip|abbr=on}},<ref name="cloud-classification" /><ref name="wmo-cloud-classification" /> are the mid-level clouds, which are given the prefix "alto-". They comprise two genera, [[altostratus cloud|altostratus]] and [[altocumulus cloud|altocumulus]]. These clouds are formed from ice crystals, supercooled water droplets, or liquid water droplets.<ref name="cloud-classification" />

Low-level clouds usually form below {{convert|6500|ft|m|order=flip|abbr=on}} and do not have a prefix.<ref name="cloud-classification" /><ref name="wmo-cloud-classification" /> The two genera that are strictly low-level are [[stratus cloud|stratus]], and [[stratocumulus cloud|stratocumulus]]. These clouds are composed of water droplets, except during winter when they are formed of [[supercooled water]] droplets or ice crystals if the temperature at cloud level is below freezing. Three additional genera usually form in the low-altitude range, but may be based at higher levels under conditions of very low humidity. They are the genera [[cumulus cloud|cumulus]], and [[cumulonimbus cloud|cumulonimbus]], and [[nimbostratus cloud|nimbostratus]]. These are sometimes classified separately as clouds of vertical development, especially when their tops are high enough to be composed of supercooled 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=Koermer, Jim | year=2011 | access-date=2 April 2012 | publisher=[[Plymouth State University]] | archive-date=10 May 2009 | archive-url=https://web.archive.org/web/20090510231716/http://vortex.plymouth.edu/clouds.html/ }}</ref><ref name="cloud-classification" />

=== Cirrocumulus ===
{{Main|Cirrocumulus cloud}}
[[File:Cirrocumulus in Hong Kong.jpg|thumb|alt=A large field of cirrocumulus clouds in a blue sky, beginning to merge near the upper left|Large field of cirrocumulus clouds|left]]

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|publisher=Georgia Institute of Technology |url=http://nenes.eas.gatech.edu/Cloud/Clouds.pdf|access-date=12 February 2011|page=2, 10–13|archive-url=https://web.archive.org/web/20110512162814/http://nenes.eas.gatech.edu/Cloud/Clouds.pdf|archive-date=12 May 2011}}</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 ===
{{Main|Cirrostratus cloud}}
[[File:Close Cirrostratus.jpg|thumb|alt=Milky-white cirrostratus clouds cause the sky to appear lighter and have a milky tint.|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|to|-45|C|F}}, the crystals tend to be long, solid, hexagonal columns. Towards the top of the cloud, at temperatures of around {{convert|-47|to|-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>{{harvnb|Hamilton|2007|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"/>