Temperature typically decreases with elevation, known as the normal lapse rate. But sometimes, the normal lapse rate is inverted, resulting in a situation where temperature increases with elevation. This is called an inversion of temperature. It is usually of short duration. The ideal situation for temperature inversion is long winter night with clear skies and still air.
The heat of the day is radiated off during the night, and by early morning hours, the earth is cooler than the air above. In polar regions, inversion is a normal year-round occurrence. It promotes stability in the lower atmosphere. It can cause smoke and dust particles to accumulate beneath the inversion layer and spread horizontally to spread the lower strata of the atmosphere, which results into dense fogs in the morning, particularly during the winter.
Inversions also occur in hills and mountains due to air drainage, where cold air produced during the night flows downhill and accumulates in valleys and low-lying areas, with warm air above. This protects plants from frost damage.