1. Insolation

The earth’s atmosphere is very much a dynamic entity. Large volumes of air are continually being moved both up and down and across the face of the Earth. As a proof, we feel air when it is in motion. There must be some energy involved here. It needs to be understood that the atmosphere is not a closed system. It is in contact with both the earth and with space, and receives energy from both directions. However, Earth itself directly contributes only a negligible amount of energy to the atmosphere, and its main role is to reflect energy from elsewhere. The ultimate sole source of atmospheric energy is in fact heat and light received through space from the Sun. This energy is known as solar insolation.

The Earth receives only a tiny fraction of the total amount of Sun’s radiations. Only two billionths or two units of energy out of 1,00,00,00,000 units of energy radiated by the sun reaches the earth’s surface due to its small size and great distance from the Sun. The unit of measurements of this energy is Langley (Ly). On an average the earth receives 1.94 calories per sq. cm per minute (2 Langley) at the top of its atmosphere.

1.1. Factors Influencing Insolation Figure 1 – effect of angle of inclination on Insolation Table 1 – Length of Day on winter and summer Solstices in the Northern Hemisphere Figure 2 – average annual insolation on the surface of the earth 1.2. Heating and Cooling of the Atmosphere Figure 3 – (a) processes of heating and cooling of atmosphere and (b) per cent share of processes in heating up of atmosphere