temperature inversion

Noun

 * 1)  An atmospheric condition in which a cooler layer of air lies below a warmer layer of air that functions as a "ceiling" for the cooler layer, interfering with normal atmospheric circulation and trapping pollutants.
 * 2) * 1952 July 30, Vern Haugland (Associated Press), "Air Force Says Saucers No Menace to US", Ludington Daily News (Michigan, USA), p. 1 (Retrieved 21 June 2012) :
 * Temperature inversions can occur in perfectly clear skies. Samford said such an inversion was present in the Washington area early last Sunday, when up to a dozen unidentified flying objects appeared on radar screens both at Washington national airport and nearby Andrews air base.
 * 1) * 2005 Dec. 13, Joe Bauman, "Wasatch's gray skies trigger a red advisory, but a storm front today could ease air pollution, Deseret News (Utah, USA) (Retrieved 21 June 2012) :
 * Bottled up by a temperature inversion, the gunk grew so dense that the Utah Division of Air Quality imposed the season's first "red" no-burn restrictions,
 * Bottled up by a temperature inversion, the gunk grew so dense that the Utah Division of Air Quality imposed the season's first "red" no-burn restrictions,

Usage notes

 * This term is sometimes encountered in the literature of ufology and other unusual phenomena, since the sharp atmospheric demarcation associated with some temperature inversions may reflect or refract light, sound, and radar waves, and thus serve as a basis for mistaken UFO sightings and other unexplained events.