1. Space Research Institute, Austrian Academy of Sciences, Graz, Austria.
2. Institut d'Estudis Espacials de Catalunya, Barcelona, Spain.
3. Instituto de Ciencias del Espacio, Barcelona, Spain.
4. Institute for Theoretical Physics, Technical University of Braunschweig, Mendelssohnstrasse 3, D-38106 Braunschweig, Germany.
5. Present address: LESIA, CNRS-Observatoire de Paris, Meudon, France.
6. Centre de Recherche Astronomique de Lyon, Lyon, France.
7. École Normale Supérieure, Lyon, France.
8. Departemento de Física Teórica, Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco, Madrid, Spain.
9. Institute for Physics, University of Graz, Graz, Austria.
10. Institute for the Study of Earth, Oceans, and Space, Durham, New Hampshire.
11. Department of Physics, University of New Hampshire, Durham, New Hampshire.