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(străt`əsfēr), second lowest layer of the earth's atmosphereatmosphere
[Gr.,=sphere of air], the mixture of gases surrounding a celestial body with sufficient gravity to maintain it. Although some details about the atmospheres of other planets and satellites are known, only the earth's atmosphere has been well studied, the science of
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. The level from which it extends outward varies with latitude; it begins c.5 1-2 mi (9 km) above the poles, c.6 or 7 mi (c.10 or 11 km) in the middle latitudes, and c.10 mi (16 km) at the equator, and extends outward c.20 mi (32 km). It is a zone of dry, thin air, cold and clear, with a horizontal temperature gradient, that, in its lower level, is the reverse of that near the earth's surface. In polar regions the temperature is −40°F; to −50°F; (−40°C; to −46°C;), but near the equator it ranges from −80°F; to below −100°F; (−62°C; to below −74°C;); in the middle latitudes it remains steady at about −67°F; (−55°C;).

The stratified variations in temperature were deduced from the behavior of sound waves transmitted through the atmosphere, which travel faster in warm air than in cold air. Weather balloonsweather balloon,
balloon used in the measurement and evaluation of mostly upper atmospheric conditions (see atmosphere). Information may be gathered during the vertical ascent of the balloon through the atmosphere or during its motions once it has reached a predetermined maximum
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 carrying electronic equipment are launched to ascertain conditions in the stratosphere; information on this atmospheric layer is also acquired from earth-orbiting satellites.

Within the stratosphere at altitudes of 12 to 30 mi (19–48 km) is the ozone layerozone layer
or ozonosphere,
region of the stratosphere containing relatively high concentrations of ozone, located at altitudes of 12–30 mi (19–48 km) above the earth's surface.
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. Its capacity to intercept most of the sun's ultraviolet rays is fundamental to the maintenance of life on the earth. Without this filtering effect, the sun's full radiation would destroy animal tissue, but sufficient ultraviolet radiation reaches the earth to support the activation of vitamin D in humans. Elevated temperatures found in the ozone layer result from its absorption of radiant energy.

Measurements of Antarctica's ozone layer have registered a consistent seasonal "hole," or thinning, in the layer above the South Pole since 1985, and since then similar thinnings have been found over other areas of the world. There is evidence that the ozone is being broken down by chlorine atoms that are released when sunlight breaks up substances such as chlorofluorocarbonschlorofluorocarbons
(CFCs), organic compounds that contain carbon, chlorine, and fluorine atoms. CFCs are highly effective refrigerants that were developed in response to the pressing need to eliminate toxic and flammable substances, such as sulfur dioxide and ammonia, in
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 (CFCs). Montreal ProtocolMontreal Protocol,
officially the Protocol on Substances That Deplete the Ozone Layer, treaty signed on Sept. 16, 1987, at Montreal by 25 nations; 197 nations are now parties to the accord.
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 and its amendments now ban these substances and have set time limits on the production of others that may also affect the ozone layer.



the layer of the atmosphere between the troposphere and the mésosphère. It extends from a height of 8–16 km to a height of 45–55 km. The temperature in the stratosphere on the whole increases with height. The gas composition of the air in the stratosphere is similar to that in the troposphere, but the stratosphere has less water vapor and more ozone (O3). The highest concentration of O3 is in the layer from 20 to 30 km.

Thermal conditions in the stratosphere are basically determined by radiative heat exchange and, to a lesser degree, by the vertical and horizontal motions of the air. As a whole, the stratosphere is close to a state of radiative equilibrium—that is, the temperature in the stratosphere is determined by the energy absorbed by the H2O, CO2, and O3 molecules being equal to the energy emitted by the molecules. The stratospheric air is heated mainly through the absorption of ultraviolet solar radiation by the ozone. On the other hand, the long-wavelength radiation of the H2O and CO2 molecules leads to cooling of the air. As a result, at low latitudes, where the quantity of H2O and CO2 is increased and there is less O3, the stratosphere is colder than over high latitudes. In mid-latitudes and high latitudes, the temperature changes little with height in the lower half of the stratosphere but increases in the upper half. Over the equator and the tropics, the temperature increases with height throughout the stratosphere. At the lower boundary of the stratosphere, the temperature varies from – 40°C (– 60°C) over the polar regions and mid-latitudes to –70°C (– 80°C) over the tropics. At the upper boundary of the stratosphere, the temperature is on the average close to 0°C.

High wind speeds and jet streams are observed in the stratosphere. In the summer, above 20–25 km, the prevailing wind direction changes from west to east. In the winter, westerly winds are found throughout the stratosphere. The greatest wind speeds are observed at the upper boundary of the stratosphere, where speeds may reach 80–100 m/sec in the winter and 60–80 m/sec in the summer.

At heights of 20–30 km, nacreous clouds are sometimes found; they apparently consist of ice crystals or supercooled droplets of water. The lower stratosphere at about 20–25 km has an increased content of aerosol particles, particularly sulfate particles from volcanic eruptions. Because of the low turbulent exchange and the absence of the washing out by precipitation, the aerosol particles have a longer lifetime here than they do in the troposphere. By increasing the atmospheric albedo, this aerosol layer of the stratosphere leads to a drop in air temperature at the earth’s surface; the decrease is particularly marked after large explosive eruptions of volcanoes.


Khvostikov, I. A. Vysokie sloi atmosfery. Leningrad, 1964. Chapter 5, subsec. 14; ch. 9, subsec. 27.
Logvinov, K. T. Meterologicheskie parametry stratosfery. Leningrad, 1970.
Table 1. Flights of manned stratosphere balloons
Date of flightCrew and countryBalloon volume (m3)Height reached (m)Dutation
May 27, 1931A. Piccard and P. Kipfer (Belgium)14,30015,78016 hr
Aug. 12, 1932A. Piccard and M. Cosyns (Belgium)14,30016,37011 hr 45 min
Sept. 30, 1933G. A. Prokot’ev, K. D. Godunov, and E. K. Birnbaum (USSR)25,00019,0008 hr 20 min
Jan. 30, 1934P. F. Fedoseenko, A. B. Vasenko, and I. D. Usyskin (USSR)25,00022,0007 hr 4 min
July 28, 1934W. Kepner, A. Stevens, and 0. Anderson (USA)85,00018,0009 hr 57 min
Aug. 18, 1934M. Cosyns and N. Van der Elst (Belgium)14,30016,00014 hr
June 26, 1935K. Ia. Zille, lu. G. Prilutskii, and A. B. Verigo (USSR)25,00016,2002 hr 37 min
Nov. 11, 1935A. Stevens and O. Anderson (USA)105,00022,0668 hr 15 min


The atmospheric shell above the troposphere and below the mesosphere; it extends, therefore, from the tropopause to about 33 miles (55 kilometers), where the temperature begins again to increase with altitude.


The layer of the atmosphere extending from the tropopause to a height of about 30 miles (50 km). The layer is characterized by a vertical isotherm (equal temperature) in the lower atmosphere followed by a temperature that increases with the height. This increase is most noticeable where the average temperature is just below 0°C. Ozone is present in a small quantity in the stratosphere.


the atmospheric layer lying between the troposphere and the mesosphere, in which temperature generally increases with height
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