[1] Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA
[2] West Virginia Univ, Dept Phys & Astron, Morgantown, WV 26506 USA
[3] Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA
[4] NASA, Goddard Space Flight Ctr, Greenbelt, MD USA
[5] Lab Atmospher & Space Phys, Boulder, CO USA
[6] Univ Toulouse, CNRS UPS CNES, IRAP, Toulouse, France