Explain the phenomenon of mirage formation in desert?

Answer 1

In deserts and in hot climate, the air near the ground becomes more hotter than air at higher levels.The refractive index of air increases with its density.Hotter air is less dense, and has and has small refractive index than cooler air.If the air currents are small,that is the air is still,the optical density of different layers of air increases with height.As a result, light from a tall object such as a tree, passes through a medium whose refractive index decreases toward the ground. thus, a ray of light from such an object successively bends away from the normal and undergoes total internal reflection, if the angle of incidence of air near the ground exceeds the critical angle. To a distant observer, the light appears to be from somewhere below the ground.

the observer naturally assumes that light is being reflected from the ground, say, by a pool of water near the tall object. Such inverted image of distant tall objects cause an optical illusion to the observer. This phenomenon is called Mirage..