The solar radiant energy is in fact the only source of energy for the basic physical processes taking place in the atmosphere and on the earth's surface. When passing through the atmosphere and being reflected by the ground surface, solar radiation undergoes changes and conversions. Some of it is absorbed in the atmosphere and converted into other forms of energy, mainly into heat, and some is scattered by gases, by dust and by water vapour. Because of absorption and scattering in the atmosphere, solar radiation is changed by the time it reaches the earth's surface. That part of it which...