1. Department of Physics and Astronomy, Dartmouth College, Hanover, New Hampshire 03755, USA
2. Department of Physics, University of Oslo, Oslo, Norway
3. Physical Sciences Department, Embry-Riddle Aeronautical University, Daytona Beach, Florida 32114, USA
4. Earth and Atmospheric Sciences, Cornell University, Ithaca, New York 14850, USA
5. Space Science Center, University of New Hampshire, Durham, New Hampshire 03824, USA