1. Earth and Space Sciences Department; University of California; Los Angeles California USA
2. Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, School of Space Science and Physics; Shandong University; Weihai China
3. School of Earth and Space Sciences; Peking University; Beijing China
4. On-leave from JPL
5. Space Science Center and Physics Department; University of New Hampshire; Durham New Hampshire USA
6. Physics Department and Geophysical Institute; University of Alaska Fairbanks; Fairbanks Alaska USA