Variations of solar spectral irradiance from near UV to the infrared - measurements and results

Solar spectral irradiance variations are known to exhibit a strong waveleng th dependence with the amount of variability increasing towards shorter wav elengths. The bulk of solar radiation is emitted at visible and infrared wa velengths. Thus, the spectral radiation length of 300 nm accounts for 99% o f the total solar radiative output. Deposited in the Earth's troposphere an d biosphere, this part of the solar irradiance spectrum determines direct s olar radiative forcing and is therefore of particular interest for climate studies. First, measurements of solar irradiance and irradiance variability from near UV to the IR are reviewed with particular emphasis on the result s obtained from the Variability of Irradiance and Gravity Oscillations (VIR GO) on SOHO and Solar Spectrum Measurement (SOLSPEC) instruments. In the se cond part a model is presented which describes solar spectral irradiance va riations in terms of the changing distribution of solar surface magnetic fe atures. (C) 2001 Elsevier Science Ltd. All rights reserved.