A Blind Source Separation Approach to the Solar Spectral Irradiance: What does the coherence of its variability tell us? Thierry Dudok de Wit [[email protected]] 1, Sean Bruinsma2, Gael Cessateur1,3, Matthieu Kretzschmar2, Jean Lilensten3, and Luis Vieira1 1 University of Orléans; 2CNES, Toulouse; and 3IPAG, Grenoble One of the striking properties of the solar spectral irradiance is the remarkable coherence of its variability, from the EUV up to the visible range. Indeed, most of the variability is captured by a few common contributions only. Various statistical techniques allow us to extract these contributions, each having different assumptions. This decomposition is directly connected to the problem of blind source separation, which has become a very fertile domain of research in acoustics and in astronomy. In the first part, we shall show how spectral irradiance observations from TIMED and SORCE can be decomposed into different contributions and what this tells us about the underlying physical processes… and also on the not-so-wanted instrumental artifacts. In the second part, we shall concentrate on the dynamical response of the solar spectral variability to the onset of active regions.