Under normal situations, in troposphere, the temperature of atmosphere decreases with increase in the altitude at a rate of 1 degree for every 165 meters. This is called normal lapse rate but on some occasions temperature increases with altitude rather than decreasing. This is called temperature inversion. This phenomenon occurs in mountainous areas during winters. During long winter nights, cold air on the mountains seeps down due to high pressure and occupies valley floors pushing warm air upwards. This leads to temperature inversion.