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temperature inversion,condition in which the temperature of the atmosphere increases with altitude in contrast to the normal decrease with altitude. When temperature inversion occurs, cold air underlies warmer air at higher altitudes. Temperature inversion may occur during the passage of a cold front or result from the invasion of sea air by a cooler onshore breeze. Overnight radiative cooling of surface air often results in a nocturnal temperature inversion that is dissipated after sunrise by the warming of air near the ground. A more long-lived temperature inversion accompanies the dynamics of the large high-pressure systems depicted on weather maps. Descending currents of air near the center of the high-pressure system produce a warming (by adiabatic compression), causing air at middle altitudes to become warmer than the surface air. Rising currents of cool air lose their buoyancy and are thereby inhibited from rising further when they reach the warmer, less dense air in the upper layers of a temperature inversion. During a temperature inversion, air pollution released into the atmosphere's lowest layer is trapped there and can be removed only by strong horizontal winds. Because high-pressure systems often combine temperature inversion conditions and low wind speeds, their long residency over an industrial area usually results in episodes of severe smog.
an increase in air temperature with increasing altitude, which is inverse to the usual decrease in temperature with altitude in the troposphere. Temperature inversions occur both near the earth’s surface (ground temperature inversions) and in the free atmosphere. Ground inversions usually form on windless nights (sometimes also during the day in winter) as a result of the intensive radiation of heat by the earth’s surface, which cools the surface itself and the adjacent layer of air. Ground inversions measure dozens and hundreds of meters thick. The increase of temperature in the inversion layer varies from tenths of a degree to more than 15°-20°C. Eastern Siberia and Antarctica have the most intense winter ground inversions. In the troposphere, above the surface layer, temperature inversions usually form in high-pressure areas owing to the sinking of air, which is accompanied by its compression and therefore heating (subsidence inversion). In the zones of atmospheric fronts, temperature inversions are created by warm air advected over the cold air beneath. In the upper layers of the atmosphere (the stratosphere, the mesosphere, and the thermosphere) temperature inversions occur as a result of the strong absorption of solar radiation. For example, at altitudes of from 20–30 to 50–60 km there is a temperature inversion related to the absorption of ultraviolet radiation of the sun by ozone. At the base of this layer the temperature ranges between — 50° and — 70°C, while at its upper boundary the temperature rises to between —10° and + 10°C. Intense temperature inversions begin at altitudes of 80–90 km and stretch for hundreds of kilometers upward; they are also caused by absorption of solar radiation.
Temperature inversions are barrier layers in the atmosphere. They obstruct the development of vertical air currents, and as a result water vapor, dust, and condensation nuclei accumulate beneath them. This leads to the formation of layers of haze, fog, and clouds. Mirages sometimes occur as a result of the anomalous refraction of light in temperature inversions. Atmospheric ducts, which promote long-distance propagation of radio waves, also form in temperature inversions.
REFERENCEKhrgian, A. Kh. Fizika atmosfery. Leningrad, 1969.
S. M. SHMETER