[1] Univ Calif Los Angeles, Inst Geophys & Planetary Phys, Los Angeles, CA 90095 USA
[2] Univ Calif Los Alamos Natl Lab, Los Alamos, NM 87544 USA
[3] NOAA, Space Environm Ctr, Boulder, CO 80305 USA
[4] Univ Calif Los Angeles, Dept Earth & Space Sci, Los Angeles, CA USA
[5] Univ Nice, Nice, France
[6] CNRS, Phys Mat Condensee Lab, F-06034 Nice, France