1. Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia 26506, USA
2. Dipartimento di Fisica, Università della Calabria, I-87036 Cosenza, Italy
3. Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716, USA
4. Department of Physics and Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20740, USA
5. Physics Department and Space Science Center, Morse Hall, University of New Hampshire, Durham, New Hampshire 03824, USA
6. NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA
7. Space Science Institute, Boulder, Colorado 80301, USA
8. T-5 Applied Mathematics and Plasma Physics Group, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA