Editing Cloud (section)

===Adiabatic cooling===
[[Adiabatic lapse rate#Dry adiabatic lapse rate|Adiabatic cooling]] occurs when one or more of three possible lifting agents – convective, cyclonic/frontal, or orographic – cause a parcel of air containing invisible water vapor to rise and cool to its dew point, the temperature at which the air becomes saturated. The main mechanism behind this process is adiabatic cooling.<ref name="adiabatic process">{{Cite web |last=Nave, R. |year=2013 |title=Adiabatic Process |url=http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/adiab.html |access-date=18 November 2013 |publisher=gsu.edu}}</ref> As the air is cooled to its dew point and becomes saturated, water vapor normally condenses to form cloud drops. This condensation normally occurs on [[cloud condensation nuclei]] such as [[salt]] or dust particles that are small enough to be held aloft by normal [[Atmospheric circulation|circulation]] of the air.<ref name="humidity, saturation, and stability">{{Cite web |last=Elementary Meteorology Online |year=2013 |title=Humidity, Saturation, and Stability |url=http://apollo.lsc.vsc.edu/~wintelsw/MET1010LOL/chapter06/ |url-status=dead |archive-url=https://web.archive.org/web/20140502055741/http://apollo.lsc.vsc.edu/~wintelsw/MET1010LOL/chapter06/ |archive-date=2 May 2014 |access-date=18 November 2013 |publisher=vsc.edu}}</ref><ref name="cloud drops">{{Cite web |last=Horstmeyer, Steve |year=2008 |title=Cloud Drops, Rain Drops |url=http://www.shorstmeyer.com/wxfaqs/float/float.html |access-date=19 March 2012}}</ref>

[[File:Cloud evolution in under a minute.ogv|thumb|upright=1.35|Animation of cloud evolution from cumulus humilis to cumulonimbus capillatus incus]]
One agent is the convective upward motion of air caused by daytime solar heating at surface level.<ref name="humidity, saturation, and stability" /> Low level airmass instability allows for the formation of cumuliform clouds in the troposphere that can produce showers if the air is sufficiently moist.<ref>{{Cite journal |last1=Freud |first1=E. |last2=Rosenfeld |first2=D. |year=2012 |title=Linear relation between convective cloud drop number concentration and depth for rain initiation |journal=Journal of Geophysical Research |volume=117 |issue=D2 |pages=n/a |bibcode=2012JGRD..117.2207F |doi=10.1029/2011JD016457 |doi-access=free | issn=0148-0227}}</ref> On moderately rare occasions, convective lift can be powerful enough to penetrate the tropopause and push the cloud top into the stratosphere.<ref name="Tropopause penetrations">{{Cite web |last1=Long, Michael J. |last2=Hanks, Howard H. |last3=Beebe, Robert G. |date=June 1965 |title=TROPOPAUSE PENETRATIONS BY CUMULONIMBUS CLOUDS |url=http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=AD0621573 |url-status=dead |archive-url=https://web.archive.org/web/20160303235551/http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=AD0621573 |archive-date=3 March 2016 |access-date=9 November 2014}}</ref>

Frontal and [[cyclonic]] lift occur in the troposphere when [[Atmospheric instability|stable]] air is forced aloft at [[weather fronts]] and around centers of [[low pressure]] by a process called [[convergence zone|convergence]].<ref name="frontal clouds">{{Cite web |last=Elementary Meteorology Online |year=2013 |title=Lifting Along Frontal Boundaries |url=http://ww2010.atmos.uiuc.edu/%28Gh%29/guides/mtr/cld/dvlp/frnt.rxml/~wintelsw/MET1010LOL/chapter06/ |access-date=20 March 2015 |publisher=vsc.edu}}</ref> [[Warm front]]s associated with extratropical cyclones tend to generate mostly cirriform and stratiform clouds over a wide area unless the approaching warm airmass is unstable, in which case cumulus congestus or cumulonimbus clouds are usually embedded in the main precipitating cloud layer.<ref name="Mackerel sky" /> [[Cold front]]s are usually faster moving and generate a narrower line of clouds, which are mostly stratocumuliform, cumuliform, or cumulonimbiform depending on the stability of the warm airmass just ahead of the front.<ref name="G&N:207-212">{{Cite book |last1=Lee M. Grenci |url=https://books.google.com/books?id=oh8lqM5obuYC&pg=PA212 |title=A World of Weather: Fundamentals of Meteorology: A Text / Laboratory Manual |last2=Jon M. Nese |publisher=Kendall/Hunt Publishing Company |year=2001 |isbn=978-0-7872-7716-1 |edition=3 |pages=207–212 |oclc=51160155}}</ref>

[[File:Dreamy Twilight.jpg|thumb|Windy evening [[twilight]] enhanced by the Sun's angle. Clouds can visually mimic a [[tornado]] resulting from orographic lift.]]
A third source of lift is wind circulation forcing air over a physical barrier such as a [[mountain]] ([[orographic lift]]).<ref name="humidity, saturation, and stability" /> If the air is generally stable, nothing more than [[lenticular cap]] clouds form. However, if the air becomes sufficiently moist and unstable, orographic showers or [[thunderstorm]]s may appear.<ref name="MT">Pidwirny, M. (2006). [http://www.physicalgeography.net/fundamentals/8e.html "Cloud Formation Processes"] {{webarchive|url=https://web.archive.org/web/20081220230524/http://www.physicalgeography.net/fundamentals/8e.html |date=20 December 2008 }}, chapter 8 in ''Fundamentals of Physical Geography'', 2nd ed.</ref>

Clouds formed by any of these lifting agents are initially seen in the troposphere where these agents are most active.  However, water vapor that has been lifted to the top of troposphere can be carried even higher by gravity waves where further condensation can result in the formation of clouds in the stratosphere and mesosphere.<ref name=Atoptics>[http://www.atoptics.co.uk/highsky/nlc2.htm About NLCs, Polar Mesospheric Clouds], from Atmospheric optics</ref>