Editing Cumulus cloud (section)

== Description ==
[[File:Brittany 01.jpg|thumb|Lines of cumulus clouds over [[Brittany]], France]]
The liquid water density within a cumulus cloud has been found to change with height above the cloud base rather than being approximately constant throughout the cloud. In one particular study, the concentration was found to be zero at cloud base. As altitude increased, the concentration rapidly increased to the maximum concentration near the middle of the cloud. The maximum concentration was found to be anything up to 1.25&nbsp;grams of water per kilogram of air. The concentration slowly dropped off as altitude increased to the height of the top of the cloud, where it immediately dropped to zero again.<ref name="Stommel94">{{harvnb|Stommel|1947|p=94}}</ref>

Cumulus clouds can form in lines stretching over {{convert|480|km|mi}} long called cloud streets. These cloud streets cover vast areas and may be broken or continuous. They form when [[wind shear]] causes horizontal circulation in the atmosphere, producing the long, tubular cloud streets.<ref name="Weston433">{{harvnb|Weston|1980|p=433}}</ref> They generally form during [[anticyclone|high-pressure systems]], such as after a cold front.<ref name="Weston437-438">{{harvnb|Weston|1980|pp=437&ndash;438}}</ref>

The height at which the cloud forms depends on the amount of moisture in the thermal that forms the cloud. Humid air will generally result in a lower cloud base. In [[Temperateness|temperate]] areas, the base of the cumulus clouds is usually below {{convert|550|m|ft}} above ground level, but it can range up to {{convert|2400|m|ft}} in altitude. In arid and mountainous areas, the cloud base can be in excess of {{convert|6100|m|ft}}.<ref name="nws-jetstream" />

Cumulus clouds can be composed of [[ice crystal]]s, water droplets, [[supercooled water]] droplets, or a mixture of them.<ref name="CRH-NOAA">{{cite web|title=Cloud Classification and Characteristics|url=http://www.crh.noaa.gov/lmk/?n=cloud_classification|url-status=dead|archive-url=https://web.archive.org/web/20121017002436/http://www.crh.noaa.gov/lmk/?n=Cloud_classification|archive-date=17 October 2012|access-date=18 October 2012|publisher=[[National Oceanic and Atmospheric Administration]]}}</ref>

One study found that in temperate regions, the cloud bases studied ranged from {{convert|500|to|1500|m|ft}} above ground level. These clouds were normally above {{convert|25|C|F}}, and the concentration of droplets ranged from {{convert|23|to|1300|/cm3|/cuin|abbr=off|adj=pre|droplets}}. This data was taken from growing isolated cumulus clouds that were not precipitating.<ref name="Warner1049">{{harvnb|Warner|1969|p=1049}}</ref> The droplets were very small, ranging down to around 5&nbsp;[[micrometre]]s in diameter. Although smaller droplets may have been present, the measurements were not sensitive enough to detect them.<ref name="Warner1051">{{harvnb|Warner|1969|p=1051}}</ref> The smallest droplets were found in the lower portions of the clouds, with the percentage of large droplets (around 20&nbsp;to 30&nbsp;micrometres) rising dramatically in the upper regions of the cloud. The droplet size distribution was slightly [[bimodal]] in nature, with peaks at the small and large droplet sizes and a slight trough in the intermediate size range. The [[skewness|skew]] was roughly neutral.<ref name="Warner1052">{{harvnb|Warner|1969|p=1052}}</ref> Furthermore, large droplet size is roughly inversely proportional to the droplet concentration per unit volume of air.<ref name="Warner1054">{{harvnb|Warner|1969|p=1054}}</ref> 

In places, cumulus clouds can have "holes" where there are no water droplets. These can occur when winds tear the cloud and incorporate the environmental air or when strong downdrafts evaporate the water.<ref name="Warner1056">{{harvnb|Warner|1969|p=1056}}</ref><ref name="Warner1058">{{harvnb|Warner|1969|p=1058}}</ref>

=== Subforms ===
[[File:Cumulusmediocrissweden.jpg|thumb|''Cumulus mediocris'' clouds over [[Sweden]]]]
Cumulus clouds come in four distinct species, ''cumulus humilis'', ''mediocris'', ''congestus'', and ''fractus''. These species may be arranged into the variety, ''cumulus radiatus''; and may be accompanied by up to seven supplementary features, ''cumulus pileus'', ''velum'', ''virga'', ''praecipitatio'', ''arcus'', ''pannus'', and ''tuba''.<ref name="WMO"/><ref name="Pretor-Pinney17">{{harvnb|Pretor-Pinney|2007|p=17}}</ref>

The species ''Cumulus fractus'' is ragged in appearance and can form in clear air as a precursor to cumulus humilis and larger cumulus species-types; or it can form in precipitation as the supplementary feature ''pannus'' (also called [[Scud (cloud)|scud]]) which can also include stratus fractus of bad weather.<ref>{{cite web|title=L7 Clouds: Stratus fractus (StFra) and/or Cumulus fractus (CuFra) bad weather|url=http://www.srh.noaa.gov/jetstream/synoptic/l7.htm|url-status=dead|archive-url=https://web.archive.org/web/20120118151256/http://www.srh.noaa.gov/jetstream/synoptic/l7.htm|archive-date=18 January 2012|access-date=11 February 2013|work=JetStream - Online School for Weather: Cloud Classifications|publisher=National Weather Service}}</ref><ref>{{cite encyclopedia|editor-first=Michael |editor-last=Allaby|encyclopedia=A Dictionary of Ecology|title=Pannus |edition=4th|year=2010 |publisher=Oxford University Press|isbn=978-0-19-956766-9|doi=10.1093/acref/9780199567669.001.0001}}</ref> ''Cumulus humilis'' clouds look like puffy, flattened shapes. ''Cumulus mediocris'' clouds look similar, except that they have some vertical development. ''Cumulus congestus'' clouds have a cauliflower-like structure and tower high into the atmosphere, hence their alternate name "towering cumulus".<ref name="TWC" /> The variety ''Cumulus radiatus'' forms in radial bands called cloud streets and can comprise any of the four species of cumulus.<ref name="Pretor-Pinney20">{{harvnb|Pretor-Pinney|2007|p=20}}</ref>

Cumulus supplementary features are most commonly seen with the species congestus. ''Cumulus virga'' clouds are cumulus clouds producing [[virga]] (precipitation that evaporates while aloft), and ''cumulus praecipitatio'' produce precipitation that reaches the Earth's surface.<ref name="Dunlop77-78">{{harvnb|Dunlop|2003|pp=77&ndash;78}}</ref> ''Cumulus pannus'' comprise shredded clouds that normally appear beneath the parent cumulus cloud during precipitation. ''Cumulus arcus'' clouds have a [[gust front]],<ref name="Ludlum473">{{harvnb|Ludlum|2000|p=473}}</ref> and ''cumulus tuba'' clouds have [[funnel clouds]] or [[tornado]]es.<ref name="Dunlop79">{{harvnb|Dunlop|2003|p=79}}</ref> ''Cumulus pileus'' clouds refer to cumulus clouds that have grown so rapidly as to force the formation of [[Pileus (meteorology)|pileus]] over the top of the cloud.<ref>{{harvnb|Garrett et al.|2006|page=i}}</ref> ''Cumulus velum'' clouds have an ice crystal veil over the growing top of the cloud.<ref name="WMO">{{Cite web|url=http://www.weatheranswer.com/public/Clouds_WMO.pdf |archive-url=https://web.archive.org/web/20050226160200/http://www.weatheranswer.com/public/Clouds_WMO.pdf |archive-date=2005-02-26 |url-status=live|access-date=18 October 2012|title=WMO classification of clouds|publisher=World Meteorological Organization}}</ref>
There are also cumulus cataractagenitus, which are formed by waterfalls.<ref>{{cite web |title=Cataractagenitus |url=https://cloudatlas.wmo.int/en/cataractagenitus.html |publisher=International Cloud Atlas}}</ref>