Solar Radiation in the Atmosphere

Abstract

In accordance with the contemporary conceptions, light (radiation) is an electromagnetic wave showing quantum properties. Thus, strictly speaking, the processes of light propagation in the atmosphere should be described within the ranges of electrodynamics and quantum mechanics. Nevertheless, it is suitable to abstract from the electromagnetic nature of light to solve a number of problems (including the problems described in this book) and to consider radiation as an energy flux. Light characteristics governed by energy are called the radiative characteristics. This approach is usual for optics because the frequency of the electromagnetic waves within the optical ranges is huge and the receiver registers only energy, received during many wave periods (not a simultaneous value of the electromagnetic intensity). The electromagnetic nature of solar radiation including the property of the electromagnetic waves to be transverse is bound up with the phenomenon of polarization, which is revealing in the relationship of the process of the interaction between radiation and substance (refraction, scattering and reflection) and configuration of the electric vector oscillations on a plane, which is normal to the wave propagation direction. Further, we are using the approximation of unpolarized radiation. The evaluation of the accuracy of this approximation will be discussed further concerning the specific problems considered in this book. The following main types of radiation (and their energy) are distinguished in radiation transferring throughout the atmosphere: direct radiation (radiation coming to the point immediately from the Sun); diffused solar radiation (solar radiation scattered in the atmosphere); reflected solar radiation from surface; self-atmospheric radiation (heat atmospheric radiation) and self-surface radiation (heat radiation). The total combination of these radiations creates the radiation field in the Earth atmosphere, which is characterized with energy of radiation coming from different directions within different spectral ranges. As is seen from above, it is possible to divide all radiation into solar and self (heat) radiation. In this book, we are considering only solar radiation in the spectral ranges 0.3−1.0 µm, where it is possible to neglect the energy of heat radiation of the atmosphere and surface, comparing with solar energy. Further with this spectral range we will be specifying the shortwave spectral range. Solar radiation integrated with respect to the wavelength over the considered