1. Space Science Division, NASA Ames Research Center, Moffett Field, California.
2. Goddard Space Flight Center, Greenbelt, Maryland.
3. Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC.
4. Department of Exploration, Arizona State University, Tempe, Arizona.
5. Laboratory for Atmospheric and Space Physics and Department of Geological Sciences, University of Colorado, Boulder, Colorado.
6. Department of Astronomy, University of Washington, Seattle, Washington.
7. Institute of Geophysics, U.C.L.A., Los Angeles, California.
8. Department of Civil and Environmental Engineering, Stanford University, Stanford, California.