1. Department of Earth, Planetary, and Space Sciences University of California Los Angeles CA USA
2. Center for Plasma Astrophysics, Department of Mathematics Katholicke University Leuven Belgium
3. Department of Physics and Astronomy University of California Los Angeles CA USA
4. Now at the Department of Physics and Astronomy West Virginia University Morgantown WV USA
5. Space Science Institute Boulder CO USA
6. NASA Goddard Space Flight Center Greenbelt MD USA