Average spectral curves of extraterrestrial solar irradiance in the (180–400) nm wavelength range

Abstract

Twenty-three spectral curves of extraterrestrial solar irradiance in the (180–400) nm wavelength range, derived from measurements taken on rockets and airborne platforms by various research groups, were examined in order to determine the average spectral curves of extraterrestrial solar irradiance. Such curves can be more reliably used in computational programmes prepared for simulating the radiative-transfer processes occurring in the terrestrial atmosphere. For each spectral curve, a careful examination was performed of the errors due to instrumental characteristics, calibration procedures, atmospheric extinction, solar limb-darkening effects, as well as to the use of normalization procedures to zero-air-mass and the mean Earth-Sun distance. These error estimates were used to obtain realistic evaluations of the standard deviations at the various wavelengths. The resulting data sets were employed to calculate the weighted mean values of the full-disk solar irradiance outside the atmosphere, for spectral resolution values of 0.4 and 1 nm. The values are presented in two tables. A further analysis was performed in order to evaluate the variability of the extraterrestrial solar irradiance as a function of solar activity, but indistinct and contradictory results were found, presumably because the experimental errors were greater than the periodical changes in the density flux of extraterrestrial solar radiation.