Figure 10 – temperature inversion

♤ Dry air: humid air absorbs the terrestrial radiation but dry air is no obstruction to terrestrial radiation and allows the radiation to escape into space.

♤ Calm atmosphere: the blowing of winds bring warm and cold air into contact. Under conditions of calm atmosphere the cold air stays put near the ground.

♤ Ice covered surface: in ice covered areas due to high albedo less insolation is received. During night due to terrestrial radiation most of the heat is lost to atmosphere and the surface is cooled. The air in contact with it is also cooled but the upper layer remains warm.

The stability of the night time temperature inversion is usually destroyed soon after sunrise as the sun's energy warms the ground, which warms the air in the inversion layer. The warmer, less dense air then rises, destroying the stability that characterizes the nightly inversion. The phenomenon of inversion of temperature is especially observed in valleys. During winters the mountain slopes cool very rapidly due to the quick radiation of heat. The air resting above them also becomes cold and its density increases. Hence, it moves down the slopes and settles down in the valleys. This air pushes the comparatively warmer air of valleys upwards and leads to the phenomenon of inversion of temperature. That is why, apple orchids in Himalayan region, tea garden of Darjeeling are found in upper slopes of the valleys.

Effect on Humans

♤ In cities, impurities present in the atmosphere such as smoke, dust particles and other pollutants do not go up in the air due to temperature inversion. They form dense fog near the earth’s surface, especially in winters. It causes problems in breathing. Frost formed may be harmful for crops in fields.

♤ At some places, people lit fire or use big blowers to mix hot and cold air in order to drain off the area of the adverse conditions created by temperature inversion.

♤ In valleys people make terraced fields in the upper slopes and also settle down there.