Portugal - Atlas do Ambiente I.3 - Radiação Solar

Summary

Radiation is an energy transfer process that requires neither physical medium for its propagation, nor contact with the radiant body. Solar radiation is the energy emitted by the Sun as electromagnetic waves. The solar radiation may be observed as «global solar radiation» corresponding to the total energy emmited by the Sun and reaching the Earth. The more common observations consist of measurements of the radiation reaching a horizontal surface, consisting of both radiation from the Sun («direct solar radiation») and that reaching the instrument by scattering in the atmosphere and clouds («diffuse sky radiation»). Solar energy is actually the cause of all physical and chemical processes occuring on Earth, which generates the weather, the oceanic circulations, the modelling of the earth crust and all the biological phenomena. The knowledge of various fluxes of radiation to and from Earth (atmosphere and Globe) is highly important for different applications including the balance of levels of radiation needed to various human activities. For climatological purposes, instantaneous values of direct solar radiation, at fixed true solar hours, are needed. 6