Stratosphere

A layer of the atmosphere that lies between about 7 and 31 mi (11 and 50 km) above the earth's surface, bounded at the bottom by the tropopause and at the top by the stratopause. Scientists became aware of the presence of the stratosphere with observations of high level dust after the eruption of Krakatoa in 1883. However, the real discovery of the stratosphere had to await Teisserenc de Bort's work of 1900.

The stratosphere is characterized by temperatures that rise with height. As a result, the air is very stable, not mixing much vertically, and allowing distinct layers of air, or strata, to form. There are also persistent regular strong winds, of which the best known are the intense western winds during the winter called the polar night jet stream.

The air in the stratosphere has much the same composition as the lower atmosphere except for a higher proportion of ozone . Absorption of incoming solar energy by this ozone makes the upper parts of the stratosphere warm and sets up the characteristic temperature gradient. The relatively high ozone concentrations are maintained by photochemical reactions. It has become clear in more recent years that other chemical reactions involving nitrogen and chlorine are also important in maintaining the ozone balance of the upper atmosphere. This balance can be easily disturbed through the input of additional nitrogen oxides and halogen compounds (from CFCs, or chlorofluorocarbons ). Transfer of gases across the tropopause into the stratosphere is rather slow, but some gases, such as CFCs and nitrous oxide , are sufficiently long-lived in the troposphere to leak across into the stratosphere and cause ozone layer depletion . Large volcanic eruptions can have sufficient force to drive gases and particles into the stratosphere where they can also disturb the ozone balance. High-flying aircraft represent another source of pollution in the stratosphere, but the lack of development of a supersonic passenger fleet has meant that this contribution has remained fairly small.

The stratosphere is extremely cold (about −112°F [−80°C]) in places, so there is relatively little water. Nevertheless, nacreous or mother-of-pearl clouds, although not frequently observed, have long been known. More recently there has been much interest in polar stratospheric clouds which had hitherto received little attention. Stratospheric cloud particles can be water-containing sulfuric acid droplets or solid nitric acid hydrates. Studies of the Antarctic ozone hole have revealed that these clouds are likely to play an important role in the depletion of ozone in the polar stratosphere.

[Peter Brimblecombe Ph.D. ]

RESOURCES

BOOKS

Chamberlain, J. W., and D. M. Hunten. Theory of Planetary Atmospheres. New York: Academic Press, 1987.

stratosphere The atmospheric layer above the troposphere, which extends on average from about 10 to 50 km above the Earth's surface. The stratosphere is a major stable layer whose base is marked by the tropopause, and where temperatures overall average approximately −60 °C. Temperature in the lower stratosphere is isothermal but increases markedly in the upper part, to reach a maximum of about 0 °C at the stratopause. High stratospheric temperatures result from absorption of ultraviolet radiation (0.20–0.32 μm wavelengths) by ozone concentrated at 15–30 km. Due to the very low air density, even the small amount of ozone concentrated in the upper stratosphere is extremely effective in absorbing radiation, thus giving high temperatures at 50 km. The isothermal condition at the base of the stratospheric inversion layer creates stability, which generally limits vertical extensions of cloud and leads to the lateral spreading of high cumulonimbus cloud with characteristic anvil heads. See also ATMOSPHERIC STRUCTURE.

stratosphere The atmospheric layer above the troposphere, which extends on average from about 10 to 50 km above the Earth's surface. The stratosphere is a major stable layer whose base is marked by the tropopause, and where temperatures overall average approximately −60°C. Temperature in the lower stratosphere is isothermal but increases markedly in the upper part, to reach a maximum of about 0°C at the stratopause. High stratospheric temperatures result from absorption of ultraviolet radiation (0.20–0.32 μm wavelengths) by ozone near the stratopause; slight vertical mixing causes some of the ozone to move downwards and it becomes concentrated at 15–30 km. Owing to the very low air density, even the small amount of ozone concentrated in the upper stratosphere is extremely effective in absorbing radiation, thus giving high temperatures at 50 km. The isothermal condition at the base of the stratospheric inversion layer creates stability, which generally limits vertical extensions of cloud and leads to the lateral spreading of high cumulonimbus cloud with characteristic anvil heads.

strat·o·sphere / ˈstratəˌsfi(ə)r/ • n. the layer of the earth's atmosphere above the troposphere, extending to about 50 km above the earth's surface (the lower boundary of the mesosphere). ∎ fig. the very highest levels of a profession or other sphere, or of prices or other quantities: her next big campaign launched her into the fashion stratosphere.DERIVATIVES: strat·o·spher·ic / ˌstratəˈsfi(ə)rik; -ˈsferik/ adj.

stratosphere Section of the Earth's atmosphere between the troposphere and the higher mesosphere. It is c.40km (25mi) thick, and for half this distance the temperature remains fairly constant. The stratosphere contains most of the atmosphere's ozone.