1. The Blackett Laboratory; Imperial College London; London UK
2. Space Sciences Laboratory; University of California; Berkeley CA USA
3. LASP/Department of Astrophysical and Planetary Sciences; University of Colorado Boulder; Boulder CO USA
4. Department of Physics and Institute for Physical Science and Technology; University of Maryland; College Park MD USA
5. Department of Physics; University of Colorado Boulder; Boulder CO USA
6. Department of Physics and Astronomy; University of Delaware; Newark DE USA
7. Now at The Department of Astronomy and Astrophysics; University of Chicago; Chicago IL USA
8. Southwest Research Institute; San Antonio TX USA
9. NASA Goddard Space Flight Center; Greenbelt MD USA
10. Department of Space and Plasma Physics; Royal Institute of Technology; Stockholm Sweden
11. Space Science Center; University of New Hampshire; Durham NH USA
12. Department of Earth, Planetary, and Space Sciences; University of California; Los Angeles CA USA