Inversion Of Temperature
Ideally, with an increase in height, temperature decreases. Under normal situations, in the troposphere, the temperature of the atmosphere decreases with an increase in the altitude at the rate of 1 degree for every 165 meters which are called normal lapse rate.
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However, there are certain conditions when the temperature increases with height instead of decreasing which is contrary to the ideal situation. This contradictory phenomenon is called temperature inversion.
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Inversion is usually of short duration but quite common nonetheless. A long winter night with clear skies and still air is ideal situation for inversion. The heat of the day radiated off during the night, and by early morning hours, the earth is cooler than the air above. Over polar areas, temperature inversion is normal throughout the year
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Surface inversion promotes stability in the lower layers of the atmosphere. Smoke and dust particles get collected beneath the inversion layer and spread horizontally to fill the lower strata of the atmosphere. Dense fogs in mornings are common occurrences especially during winter season. This inversion commonly lasts for few hours until the sun comes up and beings to warm the earth.
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The inversion takes place in hills and mountains due to air drainage. Cold air at the hills and mountains, produced during night, flows under the influence of gravity. Being heavy and dense, the cold air acts almost like water and moves down the slope to pile up deeply in pockets and valley bottoms with warm air above. This is called air drainage. It protects plants from frost damages.