Editing Mesosphere (section)

{{Short description|Layer of the atmosphere directly above the stratosphere and below the thermosphere}}
{{Use dmy dates|date=September 2019}}
{{About|the atmospheric layer}}
[[File:Antarctic_aurora_ESA313457.jpg|thumb|upright=1.5|Earth's atmosphere as it appears from space, as bands of different colours at the horizon. From the bottom, [[afterglow]] illuminates the [[troposphere]] in orange with silhouettes of clouds, and the [[stratosphere]] in white and blue. Next the '''mesosphere''' (pink area) extends to just below the [[Kármán line|edge of space]] at one hundred kilometers and the pink line of [[airglow]] of the lower [[thermosphere]] (dark), which hosts green and red [[aurora]]e over several hundred kilometers.]]

[[File:Atmosphere layers-en.svg|thumb|upright=0.5|Diagram showing the five primary layers of the Earth's atmosphere: [[exosphere]], [[thermosphere]], mesosphere, [[stratosphere]], and [[troposphere]]. From Earths surface to the top of the stratosphere (50&nbsp;km) is just under 1% of Earth's radius.]]

The '''mesosphere''' ({{IPAc-en|ˈ|m|ɛ|s|ə|s|f|ɪər|,_|ˈ|m|ɛ|z|-|,_|ˈ|m|iː|s|ə|-|,_|-|z|ə|-}};<ref>{{cite Dictionary.com|mesosphere}}</ref> {{etymology|grc|''{{wikt-lang|grc|μέσος}}'' ({{grc-transl|μέσος}})|middle||-[[sphere]]}}) is the third layer of the [[atmosphere]], directly above the [[stratosphere]] and directly below the [[thermosphere]]. In the mesosphere, [[temperature]] decreases as [[altitude]] increases. This characteristic is used to define limits: it begins at the top of the stratosphere (sometimes called the [[stratopause]]), and ends at the [[mesopause]], which is the coldest part of [[Earth's atmosphere]], with temperatures below {{cvt|-143|C|F K}}. The exact upper and lower boundaries of the mesosphere vary with latitude and with season (higher in winter and at the tropics, lower in summer and at the poles), but the lower boundary is usually located at altitudes from {{cvt|47|to|51|km|mi ft}} above [[sea level]], and the upper boundary (the mesopause) is usually from {{cvt|85|to|100|km|mi ft}}.<ref>{{Cite web|url=http://www.antarctica.gov.au/about-antarctica/environment/atmosphere/middle-atmosphere|title=Middle atmosphere|website=www.antarctica.gov.au|access-date=17 June 2018}}</ref><ref>{{Cite journal|last1=Venkat Ratnam|first1=M.|last2=Patra|first2=A. K.|last3=Krishna Murthy|first3=B. V.|date=25 March 2010|title=Tropical mesopause: Is it always close to 100&nbsp;km?|journal=[[Journal of Geophysical Research]]|volume=115|issue=D6|pages=D06106|doi=10.1029/2009jd012531|bibcode=2010JGRD..115.6106V|issn=0148-0227|doi-access=free}}</ref><ref>{{Cite web|url=https://scied.ucar.edu/shortcontent/mesosphere-overview|title=The Mesosphere - overview |publisher=[[University Corporation for Atmospheric Research|UCAR]] Center for Science Education|website=scied.ucar.edu|access-date=17 June 2018}}</ref><ref>{{Cite journal|last1=von Zahn|first1=U.|last2=Höffner|first2=J.|last3=Eska|first3=V.|last4=Alpers|first4=M.|date=1 November 1996|title=The mesopause altitude: Only two distinctive levels worldwide?|journal=[[Geophysical Research Letters]]|volume=23|issue=22|pages=3231–34|doi=10.1029/96gl03041|bibcode=1996GeoRL..23.3231V|issn=0094-8276}}</ref>

The stratosphere and mesosphere are sometimes collectively referred to as the "middle atmosphere",<ref>{{Cite web|url=https://atmos.washington.edu/academic/midatmos.html|title=Middle Atmosphere Meteorology|publisher=[[University of Washington]]|website=atmos.washington.edu|access-date=19 December 2018}}</ref> which spans altitudes approximately between {{cvt|12|and|80|km|mi}} above Earth's surface. The [[mesopause]], at an altitude of {{cvt|80|–|90|km|mi}}, separates the mesosphere from the [[thermosphere]]—the second-outermost layer of Earth's atmosphere. On Earth, the mesopause nearly co-incides with the [[turbopause]], below which different chemical species are well-mixed due to turbulent [[eddy (fluid dynamics)|eddies]]. Above this level the atmosphere becomes non-uniform because the [[scale height]]s of different chemical species differ according to their [[molecular mass]]es.

The term ''[[near space]]'' is also sometimes used to refer to altitudes within the mesosphere. This term does not have a technical definition, but typically refers to the region roughly between the [[Armstrong limit]] (about 62,000 ft or 19 km, above which humans require a [[pressure suit]] in order to survive) and the [[Kármán line]] (where [[astrodynamics]] must take over from [[aerodynamics]] in order to achieve flight); or, by another definition, to the space between the highest altitude commercial [[airliner]]s fly at (about 40,000 ft (12.2 km)) and the lowest perigee of [[satellite]]s being able to orbit the Earth (about 45 mi (73 km)). Some sources distinguish between the terms "near space" and "upper atmosphere", so that only the layers closest to the Kármán line are described as "near space".