1. Grupo de Óptica Atmosférica; University of Valladolid; Valladolid Spain
2. Group of Environmental Physics; University of Girona; Girona Spain
3. Instituto Pirenaico de Ecología, Consejo Superior de Investigaciones Científicas; Zaragoza Spain
4. Department of Physics; University of Extremadura; Badajoz Spain
5. Évora Geophysics Centre and Department of Physics; University of Évora; Évora Portugal
6. Institute for Atmospheric and Climate Science, ETH Zurich; Zurich Switzerland