Stratosphere
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The stratosphere (from the Latin stratus, meaning 'a spreading out') is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. It is stratified in temperature, with warmer layers higher up and cooler layers farther down. This is in contrast to the troposphere near the Earth's surface, which is cooler higher up and warmer farther down. The border of the troposphere and stratosphere, the tropopause, is marked by where this inversion begins, which in terms of atmospheric thermodynamics is the equilibrium level. The stratosphere is situated between about 10 km (6 miles) and 50 km (31 miles) altitude above the surface at moderate latitudes, while at the poles it starts at about 8 km (5 miles) altitude.
Temperature
The stratosphere is layered in temperature because it is heated from above by absorption of ultraviolet radiation from the Sun. Within this layer, temperature increases as altitude increases (see temperature inversion); the top of the stratosphere has a temperature of about 270 K (−3°C or 29.6°F), just slightly below the freezing point of water.[1] This top is called the stratopause, above which temperature again decreases with height. The vertical stratification, with warmer layers above and cooler layers below, makes the stratosphere dynamically stable: there is no regular convection and associated turbulence in this part of the atmosphere. The heating is caused by an ozone layer that absorbs solar ultraviolet radiation, heating the upper layers of the stratosphere. The base of the stratosphere occurs where heating by conduction from above and cooling by convection from below (through the troposphere, due to the adiabatic expansion of air parcels) balance out; hence, the stratosphere begins at lower altitudes near the poles due to the lower ground temperature.The major reason for the temperature increase with altitude is that most of the ozone (O3) is contained in the stratosphere. High energy ultraviolet light interacts with ozone to cause the temperature increase.
Circulation and mixing
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The stratosphere is a region of intense interactions among radiative, dynamical, and chemical processes, in which horizontal mixing of gaseous components proceeds much more rapidly than vertical mixing.
An interesting feature of stratospheric circulation is the quasi-Biennial Oscillation (QBO) in the tropical latitudes, which is driven by gravity waves that are convectively generated in the troposphere. The QBO induces a secondary circulation that is important for the global stratospheric transport of tracers such as ozone or water vapor.
In northern hemispheric winter, sudden stratospheric warmings can often be observed which are caused by the absorption of Rossby waves in the stratosphere.
Life
Bacterial life survives in the stratosphere, making it a part of the biosphere.[2] Also, some bird species have been reported to fly at the lower levels of the stratosphere. On November 29, 1975, a Rüppell's Vulture was reportedly ingested into a jet engine 37,900 feet above the Ivory Coast, and Bar-headed geese routinely overfly Mount Everest's summit, which is 29,028 feet.[3][4]
See also
- Léon Teisserenc de Bort and Richard Assmann (the discoverers of the stratosphere)
- Paris Gun (first artificial object to reach stratosphere)
- SR-71 Blackbird
- Concorde
- Lockheed U-2
- RQ-4 Global Hawk
- Twinjets service ceiling
- Le Grand Saut
References
- ^ Seinfeld, J. H., and S. N. Pandis, (2006), Atmospheric Chemistry and Physics: From Air Pollution to Climate Change 2nd ed, Wiley, New Jersey
- ^ S. Shivaji et al, "Isolation of three novel bacterial strains, Janibacter hoylei sp. nov., Bacillus isronensis sp. nov. and Bacillus aryabhattai sp. nov. from cryotubes used for collecting air from upper atmosphere.", Int J Syst Evol Microbiol, 2009.
- ^ [1]
- ^ Thomas Alerstam, David A. Christie, Astrid Ulfstrand. Bird Migration (1990). Page 276.