1. D. A. Gurnett and W. S. Kurth, Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242, USA.
2. A. Roux, Centre d'Etudes des Environnements Terrestre et Planetaires, Universite Versailles Saint Quentin, 10/12 Avenue de l'Europe, 78140 Velizy, France.
3. S. J. Bolton, Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109, USA.
4. C. F. Kennel, Office of the Chancellor, University of California, Los Angeles, CA 90095, USA.