Editing Contrail (section)

{{short description|Long, thin artificial clouds that sometimes form behind aircraft}}
{{redirect|Vapor trail|other uses|Vapor Trail (disambiguation)}}
{{Distinguish|Chemtrail conspiracy theory}}
{{Other uses}}
{{Use dmy dates|date=September 2019}}
{{Infobox Cloud
|name           = Contrails
|image location = File:Jet-contrails-tokyosky-japan-2018.webm
|image name     = A jet forming contrails in a blue sky
|abbreviation   =
|symbol         =
|genus          = Cirrus (''curl of hair''), cirrocumulus, or cirrostratus
|species        =
|variety        =
|altitude_m     = 7,500 to 12,000
|altitude_ft    = 25,000 to 40,000
|level          = high
|appearance     = Long bands
|precipitation  = No
| thickness      =
| Ice content    =
}}
'''Contrails''' ({{IPAc-en|ˈ|k|ɒ|n|t|r|eɪ|l|z}}; short for "condensation trails") or '''vapour trails''' are line-shaped [[clouds]] produced by [[aircraft]] engine exhaust or changes in [[air pressure]], typically at aircraft cruising altitudes several kilometres/miles above the [[Earth|Earth's]] surface. They are composed primarily of [[water]], in the form of [[Ice crystal|ice crystals]]. The combination of [[water vapor]] in aircraft engine exhaust and the low ambient temperatures at high altitudes causes the trails' formation. [[Chemical impurity|Impurities]] in the engine exhaust from the fuel, including [[soot]] and [[sulfur]] compounds (0.05% by weight in jet fuel) provide some of the particles that serve as [[cloud condensation nuclei]] for [[water droplet]] growth in the exhaust. If water droplets form, they can freeze to form ice particles that compose a contrail.<ref name="FAA.GOV">{{cite web |url=https://www.faa.gov/sites/faa.gov/files/regulations_policies/policy_guidance/envir_policy/contrails.pdf |archive-url=https://web.archive.org/web/20060928114935/http://www2.faa.gov/regulations_policies/policy_guidance/envir_policy/media/contrails.pdf |archive-date=2006-09-28 |url-status=live |title=Aircraft Contrails Factsheet |publisher=FAA.Gov |access-date=10 September 2023}}</ref> Their formation can also be triggered by changes in air pressure in [[wingtip vortices]], or in the air over the entire wing surface.<ref>{{cite encyclopedia |title=vapour trail |url=https://www.britannica.com/EBchecked/topic/623212/vapour-trail |encyclopedia=Encyclopædia Britannica |publisher=Encyclopædia Britannica Inc. |access-date=17 April 2012}}</ref> Contrails, and other clouds caused directly by human activity, are called '''''homogenitus'''''.<ref name=ICA2017>{{cite news |last1=Sutherland |first1=Scott |title=Cloud Atlas leaps into 21st century with 12 new cloud types |url=https://www.theweathernetwork.com/news/articles/cloud-atlas-leaps-into-21st-century-with-12-new-cloud-types/80685/ |access-date=24 March 2017 |work=The Weather Network |agency=Pelmorex Media |date=23 March 2017 |archive-date=31 May 2022 |archive-url=https://web.archive.org/web/20220531022305/https://www.theweathernetwork.com/news/articles/cloud-atlas-leaps-into-21st-century-with-12-new-cloud-types/80685/ |url-status=dead }}</ref>

The vapor trails produced by [[Rocket|rockets]] are referred to as "'''missile contrails'''"<ref>{{Cite web |date=2013-10-17 |title=The Russian Missile Contrail You May Have Missed During the Shutdown |url=https://earthobservatory.nasa.gov/blogs/earthmatters/2013/10/17/the-missile-contrail-you-may-have-missed-during-the-shutdown/ |archive-url=https://web.archive.org/web/20250217051509/https://earthobservatory.nasa.gov/blogs/earthmatters/2013/10/17/the-missile-contrail-you-may-have-missed-during-the-shutdown/ |archive-date=17 Feb 2025 |access-date=2025-02-28 |website=earthobservatory.nasa.gov |publisher=[[NASA Earth Observatory]] |language=en}}</ref> or "'''rocket contrails'''." The water vapor and aerosol produced by rockets promote the "formation of [[Ice cloud|ice clouds]] in ice [[Supersaturation|supersaturated]] layers of the atmosphere."<ref name=":0">{{Cite journal |last=Li |first=Chenshuo |last2=Fu |first2=Debin |last3=Wei |first3=Tianyu |date=2025-02-21 |title=Random walk dispersion model for missile contrail particles in cross-airspace environments |url=https://www.sciencedirect.com/science/article/pii/S2214914725000546 |journal=Defence Technology |doi=10.1016/j.dt.2025.02.015 |issn=2214-9147}}</ref><ref>{{Cite journal |last=Voigt |first=Ch. |last2=Schumann |first2=U. |last3=Graf |first3=K. |date=2016-07-01 |title=Contrail formation in the tropopause region caused by emissions from an Ariane 5 rocket |url=https://ui.adsabs.harvard.edu/abs/2016EUCAS...8..183V/abstract |journal=EUCASS Proceedings Series |volume=8 |pages=183–196 |doi=10.1051/eucass/201608183}}</ref> Missile contrail clouds mainly comprise "[[Oxide|metal oxide]] particles, high-temperature water vapor condensation particles, and other byproducts of [[Rocket engine|engine combustion]]."<ref name=":0" />

Depending on the temperature and humidity at the altitude where the contrails form, they may be visible for only a few seconds or minutes, or may persist for hours and spread to be several kilometres/miles wide, eventually resembling natural [[cirrus cloud|cirrus]] or [[altocumulus]] clouds.<ref name="FAA.GOV"/> '''Persistent contrails''' are of particular interest to scientists because they increase the cloudiness of the atmosphere.<ref name="FAA.GOV"/> The resulting cloud forms are formally described as '''homomutatus''',<ref name=ICA2017/> and may resemble cirrus, cirrocumulus, or cirrostratus, and are sometimes called '''cirrus aviaticus'''.<ref>{{cite web |title=Cirrus Aviaticus – Cirrus – Names of Clouds |url=http://namesofclouds.com/cirrus/cirrus-aviaticus.html |website=namesofclouds.com |access-date=13 October 2021}}</ref> Some persistent spreading contrails contribute to [[climate change]].<ref>{{Cite web |last=Timperley |first=Jocelyn |title=The fastest ways aviation could cut emissions |url=https://www.bbc.com/future/article/20210525-how-aviation-is-reducing-its-climate-emissions |access-date=2021-06-11 |website=www.bbc.com |language=en}}</ref>