Measurement and Models of Solar Irradiance

Solar radiation is a general term that, in this book stands, for the electromagnetic radiation emitted by the sun. The total amount of solar radiation received at normal incidence at the top of the earth¿s atmosphere, at the mean sun-earth distance, is referred to as the Total Solar Irradiance (TSI) or extraterrestrial solar irradiance. The TSI varies over time, albeit by a small amount, and its magnitude and variations directly or indirectly affects many atmospheric and biological processes on earth. Since November 1978 a complete set of TSI measurements from various space borne radiometers is available, yielding a time series of 26 years. FIGURE 1.1 shows the measured time series, consisting of mean daily values plotted from the composite data set version d30_60_040 from PMOD/WRC and with reference to Fröhlich et al. in [10., 1998]1 and Fröhlich in [12., 2003]. For the duration of this test, 17 November 1978 to 20 April 2004, the absolute minimum and maximum daily TSI were 1362Wm-2 and 1368Wm-2, respectively. Following the work of Gueymard in [15., 2004] an estimate of the mean TSI for the above period is made.