[1] Vikram Sarabhai Space Ctr, Space Phys Lab, Planetary Sci Branch, Trivandrum 695022, Kerala, India
[2] Max Planck Inst Solar Syst Res, D-37191 Katlenburg Lindau, Germany
[3] Tohoku Univ, Grad Sch Sci, Dept Geophys, Aoba Ku, Sendai, Miyagi 9808578, Japan
[4] Univ So Calif, Dept Phys & Astron, Ctr Space Sci, Los Angeles, CA 90089 USA