Mesosphere

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 edge of space at one hundred kilometers and the pink line of airglow of the lower thermosphere (dark), which hosts green and red aurorae over several hundred kilometers.
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 km) is just under 1% of Earth's radius.

The mesosphere (/ˈmɛsəsfɪər, ˈmɛz-, ˈmsə-, -zə-/;[1] from Ancient Greek μέσος (mésos) 'middle' and -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 −143 °C (−225 °F; 130 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 47 to 51 km (29 to 32 mi; 154,000 to 167,000 ft) above sea level, and the upper boundary (the mesopause) is usually from 85 to 100 km (53 to 62 mi; 279,000 to 328,000 ft).[2][3][4][5]

The stratosphere and mesosphere are sometimes collectively referred to as the "middle atmosphere",[6] which spans altitudes approximately between 12 and 80 km (7.5 and 49.7 mi) above Earth's surface. The mesopause, at an altitude of 80–90 km (50–56 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 eddies. Above this level the atmosphere becomes non-uniform because the scale heights of different chemical species differ according to their molecular masses.

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 airliners fly at (about 40,000 ft (12.2 km)) and the lowest perigee of satellites 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".

  1. ^ "mesosphere". Dictionary.com Unabridged (Online). n.d.
  2. ^ "Middle atmosphere". www.antarctica.gov.au. Retrieved 17 June 2018.
  3. ^ Venkat Ratnam, M.; Patra, A. K.; Krishna Murthy, B. V. (25 March 2010). "Tropical mesopause: Is it always close to 100 km?". Journal of Geophysical Research. 115 (D6): D06106. Bibcode:2010JGRD..115.6106V. doi:10.1029/2009jd012531. ISSN 0148-0227.
  4. ^ "The Mesosphere - overview". scied.ucar.edu. UCAR Center for Science Education. Retrieved 17 June 2018.
  5. ^ von Zahn, U.; Höffner, J.; Eska, V.; Alpers, M. (1 November 1996). "The mesopause altitude: Only two distinctive levels worldwide?". Geophysical Research Letters. 23 (22): 3231–34. Bibcode:1996GeoRL..23.3231V. doi:10.1029/96gl03041. ISSN 0094-8276.
  6. ^ "Middle Atmosphere Meteorology". atmos.washington.edu. University of Washington. Retrieved 19 December 2018.

Mesosphere

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