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Attenuation of the Solar Radiation in the Atmosphere

The electromagnetic radiation of the sun which impinges on the upper layers of the earth's atmosphere is referred to as extraterrestrial solar radiation. The sun shines at an angle of vision of 32' so that the extraterrestrial solar radiation is practically parallel. As it passes through the atmosphere, the extraterres¬ trial solar radiation is attenuated by extinction, i.e. by scattering and absorption by the air molecules, the aerosol particles and the cloud droplets and crystals. That part of the extraterrestrial solar radiation which reaches the surface of the earth unscattered is referred to as direct solar radiation. The different regions of the solar radiation spectrum are affected to differing extents by this extinction.