The temperature decreases along with elevation in normal circumstances within the troposphere. But in certain special circumstances, the temperature increases along with elevation rather than decreasing. Increase in temperature along with altitude is called inversion of temperature or inversion. For the process of inversion of temperature, long nights, clear sky, calm air, dry air and glacial conditions, etc. are ideal geographical conditions.
Under such circumstances, heat radiation from the lower layers of the surface and air occurs at a faster pace. As a result, the lower layer becomes thick and dense due to the wind being cold. The upper air in which heat radiation is slow, is relatively hot. In such a situation, the temperature increases instead of decreasing along with decrease in height.
