Insolation :

               Insolation is the amount of diffused and direct solar radiation which reaches the Earth's surface. The insolation received by the Earth is in short wave form and it heats up the Earth's surface. The Earth after being heated, itself becomes a radiating body and it radiates energy to the atmosphere in long wave form. This energy heats up  the atmosphere from below. This energy is known as terrestrial radiation.

               The terrestrial radiation is responsible for movement of air and currents, evaporation, precipitation, recycling and of nutrients and elements.

    Solar Insolation is discharged from the sun in the form of-

(i)  Very short wave length X- rays, gamma rays and ultraviolet rays.

(ii) Visible light rays.

(iii) Short wave length, infrared rays.

(iv) Long wave length, microwave length and radio waves.

             

              The amount of solar Insolation received on a unit area of the surface of the earth is more or less constant which is known as solar constant. The value of solar constant is 2g calories per sq cm/min. It is also expressed in terms of Langley as 2langley/min.