Exergy of solar radiation: global scale

Abstract

A new concept regarding the exergy of solar radiation [Ecol. Model. 145 (1991) 101] is applied to the analysis of satellite data describing the seasonal (monthly) dynamics of four components of the global radiation balance: incoming and outgoing short- and long-wave solar radiation. Stated in general terms, the incoming and outgoing radiation are described by the energy spectra E in( ν) and E out( ν) for any point of the globe. We assume that there exists a non-linear operator which transforms E in( ν) into E out( ν). Its properties are defined by the characteristics of a reflecting surface (ocean, ice, land, vegetation, etc.). It is suggested that exergy, which is properly a generalised Kullback measure of the information increment, is such an operator. It is also shown that such standard values as the radiation balance and albedo are characteristics of a linear transformation operator. Using NASA satellite data to calculate the global distribution of the annual mean of exergy, we see that the domains with maximal values of exergy correspond to the main upwellings of the ocean. If thermodynamics analogies are applied to the process of interaction of solar radiation with an “active” planetary surface, in particular with vegetation cover, then the difference between the radiation balance and the exergy can be considered as the increment of internal energy. It is shown that the global pattern of this value is very similar to the global vegetation pattern.