1. Physikalisches Institut, Universität Bern, 3012 Bern, Switzerland
2. Department of Physics, University of Maryland, College Park, MD 20742
3. Office of Space Science and Applications, National Aeronautics and Space Administration, Washington, DC 20546
4. Institut für Datenverarbeitende Anlagen, Technische Universität, 3300 Braunschweig, Germany
5. Max-Planck-Institut für Aeronomie, 3411 Katlenburg-Lindau, Germany
6. National Aeronautics and Space Administration, Goddard Space Flight Center, Greenbelt, MD 20770