Total solar irradiance variations since 1978

A composite record of solar total irradiance compiled from measurements made by five independent space-based radiometers since 1978 is the basis for an evaluation of the influence of solar activity on total solar irradiance. An empirical model that parameterizes the combined influences of dark sunspots and bright faculae features on solar irradiance is able to explain more than 95% of the variance. After removing the magnetic influence with the model, the remaining 'quiet sun' shows no trend over the whole period, indicating that the sun has not changed over the past two solar cycles. The inclusion of p-mode frequency changes in the model does not explain more than already expained by the magnetic parameters. (C) 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved.