1. Max–Planck–Institut für Physik Komplexer Systeme, Nöthnitzer Strasse 38, D–01187 Dresden, Germany
2. Mathematical Institute, University of Oxford, Oxford OX1 3LB, UK
3. Institute for Scientific Interchange Foundation, Viale San Severo 65, I–10133 Turin, Italy
4. 4Department of Solar Energy and Environmental Physics, Blaustein Institute for Desert Research, Ben Gurion University, Sede Boker Campus 84990, Israel
5. Department of Physics, Ben Gurion University, Beer Sheva 84105, Israel
6. 6Institute of Atmospheric Sciences and Climate, National Research Council, Corso Fiume 4, I–10133 Turin, Italy