1. Center for Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139.
2. NASA-Goddard Space Flight Center, Greenbelt, MD 20771.
3. Imperial College, London, England.
4. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109.
5. Max-Planck-Institüt für Aeronomie, Katlenburg-Lindau, Federal Republic of Germany.
6. Department of Atmospheric Science, University of California, Los Angeles, CA 90024.
7. Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242.
8. Department of Geophysics and Planetary Sciences, Tel Aviv University, Tel Aviv, Israel.