1. Institut für Geophysik und Meteorologie, Universität zu Köln, Albertus Magnus Platz, 50678 Cologne, Germany.
2. Space and Atmospheric Physics, Blackett Laboratory, Imperial College London, Prince Consort Road, London SW7 2AZ, UK.
3. Centre d'Etude Spatiale des Rayonnements, Université Paul Sabatier, Toulouse, France.
4. Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109–8099, USA.
5. Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095–1567, USA.