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Atmosphere diagram showing stratosphere. The layers are to scale: from Earth's surface to the top of the stratosphere (50km) is just under 1% of Earth's radius. (click to enlarge)

The stratosphere 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.

The word stratosphere is from the Greek meaning 'stratified layer' and sphaira meaning ball.

Contents

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.

Aircraft flight

Commercial airliners typically cruise at altitudes of 9–12 km in temperate latitudes, in the lower reaches of the stratosphere.[2] They do this to optimize jet engine fuel burn, mostly thanks to the low temperatures encountered near the tropopause. It also allows them to stay above any hard weather, and avoid atmospheric turbulence from the convection in the troposphere. Turbulence experienced in the cruise phase of flight is often caused by convective overshoot from the troposphere below. Although a few gliders have achieved great altitudes in the powerful thermals in thunderstorms, this is dangerous. Most high altitude flights by gliders use lee waves from mountain ranges and were used to set the current record of 15,447m (50,671 feet).

Circulation and mixing

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.[3]

See also

References

  1. ^ Seinfeld, J. H., and S. N. Pandis, (2006), Atmospheric Chemistry and Physics: From Air Pollution to Climate Change 2nd ed, Wiley, New Jersey
  2. ^ Altitude of a Commercial Jet
  3. ^ 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.

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