1. Department of Physics, University of Colorado, Boulder, CO 80309, USA.
2. Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80303, USA.
3. ESA-ESAC, E-28691 Villanueva de la Cañada, Madrid, Spain.
4. Institut für Geologische Wissenschaften, Freie Universität Berlin, Berlin, Germany.
5. Space Physics and Astronomy Research Unit, University of Oulu, Oulu, Finland.
6. Space Science Division, NASA Ames Research Center, Moffett Field, CA 94035, USA.
7. Institut für Raumfahrtsysteme, Universität Stuttgart, Stuttgart, Germany.