1. ISAS, Department of Physics and Engineering Physics, 116 Science Place, University of Saskatchewan, Saskatoon, SK S7N 5E2, Canada.
2. NorthWest Research Associates Inc., 4118 148 Avenue N.E., Redmond, WA 98052, USA.
3. Centre for Research in Earth and Space Science, York University, 4700 Keele Street, Toronto, ON M3J 1P3, Canada.