View source for Mesosphere

{{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".

==Temperature==
Within the mesosphere, [[temperature]] decreases with increasing [[height]]. This is a result of decreasing absorption of solar radiation by the rarefied atmosphere having a [[Ozone–oxygen_cycle#Mesosphere|diminishing relative ozone concentration]] as altitude increases (ozone being the main absorber in the UV wavelengths that survived absorption by the thermosphere).<ref name="Photochemistry of Ozone">[https://slideplayer.com/slide/10904550/ Photochemistry of Ozone]</ref> Additionally, this is also a result of increasing cooling by [[Carbon dioxide|CO<sub>2</sub>]] [[radiative emission]]. The top of the mesosphere, called the [[mesopause]], is the coldest part of Earth's atmosphere.<ref>{{GoldBookRef|title=mesosphere|file=M03855}}</ref> Temperatures in the upper mesosphere fall as low as about {{convert|-100|C|K F|sigfig=3}},<ref>{{Citation|title=Mesosphere (Wayback Machine Archive)|url=http://www.ace.mmu.ac.uk/eae/atmosphere/older/mesosphere.html|access-date=14 November 2011|publisher=Atmosphere, Climate & Environment Information ProgGFKDamme (UK [[Department for Environment, Food and Rural Affairs]])|url-status=dead|archive-url=https://web.archive.org/web/20100701030705/http://www.ace.mmu.ac.uk/eae/atmosphere/older/mesosphere.html|archive-date=1 July 2010}}</ref> varying according to [[latitude]] and [[season]].

==Dynamic features==
[[File:ISS-46 Soyuz TMA-17M reentry.jpg|thumb|300px|[[Afterglow]] of the [[troposphere]] (orange), the [[stratosphere]] (blue) and the '''mesosphere''' (dark) at which [[atmospheric entry]] begins, leaving smoke trails, such as in this case of a [[spacecraft]] reentry.]]
The main most important features in this region are strong zonal (East-West) winds, [[atmospheric tide]]s, internal atmospheric gravity waves (commonly called "[[gravity waves]]"), and [[planetary wave]]s. Most of these tides and waves start in the [[troposphere]] and lower [[stratosphere]], and propagate to the mesosphere. In the mesosphere, gravity-wave amplitudes can become so large that the waves become unstable and dissipate. This dissipation deposits momentum into the mesosphere and largely drives global circulation.

[[Noctilucent cloud]]s are located in the mesosphere. The upper mesosphere is also the region of the [[ionosphere]] known as the ''D layer'', which is only present during the day when some [[ionization]] occurs with [[nitric oxide]] being ionized by [[Lyman series]]-alpha hydrogen radiation. The ionization is so weak that when night falls, and the source of ionization is removed, the free electron and [[ion]] form back into a neutral molecule.

A {{convert|5|km|mi ft|abbr=on}} deep [[sodium layer]] is located between {{convert|80|-|105|km|abbr=on|mi ft}}. Made of unbound, non-ionized atoms of sodium, the sodium layer radiates weakly to contribute to the [[airglow]]. The sodium has an average concentration of 400,000 atoms per cubic centimetre. This band is regularly replenished by sodium [[Sublimation (phase transition)|sublimating]] from incoming meteors. Astronomers have begun utilizing this sodium band to create "guide stars" as part of the [[adaptive optics|adaptive optical correction process]] used to produce ultra-sharp ground-based observations.<ref>{{cite web| url = http://www.laserfocusworld.com/articles/print/volume-52/issue-07/features/adaptive-optics-eso-s-very-large-telescope-sees-four-times-first-laser-light.html| title = Martin Enderlein et al., ''ESO's Very Large Telescope sees four times first light'', Laser Focus World, July 2016, pp. 22-24| date = 11 July 2016}}</ref> Other metal layers, e.g. iron and potassium, exist in the upper mesosphere/lower thermosphere region as well.

Beginning in October 2018,<ref>The "dunes" were first spotted by photographers in Finland and Sweden.</ref> a distinct type of [[aurora]] has been identified, originating in the mesosphere. Often referred to as 'dunes' due to their resemblance to sandy ripples on a beach, the green undulating lights extend toward the equator. They have been identified as originating about {{convert|96|km|abbr=on|mi ft}} above the surface. Since auroras are caused by ultra-high-speed solar particles interacting with atmospheric molecules, the green color of these dunes has tentatively been explained by the interaction of those solar particles with oxygen molecules. The dunes therefore occur where mesospheric oxygen is more concentrated.<ref>{{cite web| url = https://www.smithsonianmag.com/smart-news/new-type-aurora-ripples-across-sky-horizontal-green-dunes-180974083/?spMailingID=41658140&spUserID=NzQwNDUzNzY2MzMS1&spJobID=1682695015&spReportId=MTY4MjY5NTAxNQS2| title = Wu, Katherine J. A New Type of Aurora Ripples Across the Sky in Horizontal Green "Dunes". Smithsonian Magazine (29 January 2020)}}</ref>

Millions of [[meteor]]s enter the Earth's atmosphere, averaging 40,000 tons per year.<ref>Leinert C.; Gruen E. (1990). "Interplanetary Dust". Physics and Chemistry in Space (R. Schwenn and E. Marsch eds.). Springer-Verlag. pp. 204-275</ref> The ablated material, called meteoric smoke, is thought to serve as condensation nuclei for [[noctilucent clouds]].

==Exploration==
The mesosphere lies above altitude records for [[aircraft]],<ref>{{cite web|url=http://www.fai.org/fai-record-file/?recordId=2825|title=Powered Aeroplanes World Records|publisher=[[Fédération Aéronautique Internationale]]|access-date=31 August 2016|url-status=dead|archive-url=https://web.archive.org/web/20160911215233/http://www.fai.org/fai-record-file/?recordId=2825|archive-date=11 September 2016}}</ref> while only the lowest few kilometers are accessible to [[balloons]], for which the altitude record is {{convert|53.0|km}}.<ref>{{cite web|url=http://www.isas.jaxa.jp/e/special/2003/yamagami/03.shtml|title=Research on Balloon to Float over 50&nbsp;km Altitude|publisher=Institute of Space and Astronautical Science, [[JAXA]]|access-date=29 September 2011}}</ref> Meanwhile, the mesosphere is below the minimum altitude for [[Geocentric orbit|orbital]] [[spacecraft]] due to high atmospheric drag.<ref>{{cite web|url=http://www.iadc-online.org/Documents/IADC-2002-01,%20IADC%20Space%20Debris%20Guidelines,%20Revision%201.pdf|title=IADC Space Debris Mitigation Guidelines|publisher=[[Inter-Agency Space Debris Coordination Committee]]|date=15 October 2002|access-date=31 August 2016|archive-url=https://web.archive.org/web/20131203014608/http://www.iadc-online.org/Documents/IADC-2002-01,%20IADC%20Space%20Debris%20Guidelines,%20Revision%201.pdf|archive-date=3 December 2013|url-status=usurped}}</ref><ref>{{cite web|url=http://www.orbitaldebris.jsc.nasa.gov/library/NSS1740_14/nss1740_14-1995.pdf|title=NASA Safety Standard 1740.14, Guidelines and Assessment Procedures for Limiting Orbital Debris|publisher=Office of Safety and Mission Assurance|date=1 August 1995 |url-status=dead |archive-url=https://web.archive.org/web/20130215143933/http://orbitaldebris.jsc.nasa.gov/library/NSS1740_14/nss1740_14-1995.pdf |archive-date=15 February 2013 }}</ref><ref>{{cite web|url=http://nccur.lib.nccu.edu.tw/handle/140.119/51133<!-- former link: http://www.fai.org/astronautics/100km.asp-->|title=100 km Altitude Boundary for Astronautics|publisher=Fédération Aéronautique Internationale}}</ref> It has only been accessed through the use of [[sounding rocket]]s, which are only capable of taking mesospheric measurements for a few minutes per mission.<ref>{{cite web|date=24 July 2006|url=http://rscience.gsfc.nasa.gov/srrov.html|title=NASA Sounding Rocket Program Overview|work=NASA Sounding Rocket Program|publisher=NASA|access-date=10 October 2006}}</ref> As a result, it is the least-understood part of the atmosphere, resulting in the humorous moniker ''ignorosphere''.<ref>{{cite web|date=1 September 2016|url=https://www.discovermagazine.com/technology/reusable-rockets-set-to-explore-the-ignorosphere|title=Reusable Rockets Set to Explore the 'Ignorosphere'|publisher=[[Discover (magazine)|Discover Magazine]]|access-date=2 April 2018}}</ref><ref>{{cite web|url=http://usatoday30.usatoday.com/news/nation/2003-02-06-atmosphere_x.htm|title=Upper atmosphere may hold clues in Columbia mystery|date=6 February 2003}}</ref> The presence of [[red sprite]]s and [[blue jet]]s (electrical discharges or [[lightning]] within the lower mesosphere), [[noctilucent cloud]]s, and density shears within this poorly understood layer are of current scientific interest.

On February 1, 2003, {{OV|102}} [[Space Shuttle Columbia disaster|broke up on reentry]] at about {{cvt|62|km}} altitude, in the lower mesosphere, killing all seven crew members.

==Phenomena in mesosphere and near space==
[[File:ISS-44_Red_Sprites,_northwest_Mexico.jpg|thumb|An astronaut onboard the [[International Space Station]] observes lightning at the horizon extending into the mesosphere as red [[sprite (lightning)|sprite]] just below the line of [[airglow]].]]
[[File:ISS028-E-8400_-_View_of_Asia.jpg|thumb|[[Noctilucent clouds]] (not to be mistaken with the slightly higher up [[airglow]]), at the upper edge of the mesosphere.]]
* [[Airglow]]
* [[Atmospheric tides]]
* [[Ionosphere]]
* [[Meteors#Meteor|Meteors]]
* [[Noctilucent clouds]]
* [[Polar aurora]]
* [[Sprite (lightning)]]
* [[Upper atmospheric lightning]] (Transient luminous event)

==See also==
* [[Aeronomy]]
* [[Amateur radio high-altitude ballooning]]
* [[Geospace]]
* [[High altitude]]
{{Clear}}

==References==
{{Reflist}}

==External links==
* [http://www.atoptics.co.uk/highsky/hmeso.htm Description with links to other atmospheric topics]
* [http://www.satinsprogram.com/ Students And Teachers In Near Space] {{Webarchive|url=https://web.archive.org/web/20180104073319/http://www.satinsprogram.com/ |date=4 January 2018 }}
* [http://www.nearspacesystems.com/ Near Space Systems]
* [http://www.spacedata.net/ Space Data Corporation]
* [http://www.bhaldi.org/ The B.H.A.L.D.I. Project] {{Webarchive|url=https://web.archive.org/web/20170211160823/http://www.bhaldi.org/ |date=11 February 2017 }}

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[[Category:Atmosphere]]
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