1. Physics Department; University of New Brunswick; Fredericton; New Brunswick; Canada
2. Department of Geodesy and Geomatics Engineering; University of New Brunswick; Fredericton, New Brunswick; Canada
3. Department of Physics and Astronomy; University of Western Ontario; London, Ontario; Canada
4. Department of Physics; University of Alberta; Edmonton, Alberta; Canada
5. Geomagnetic Laboratory; Natural Resources Canada; Ottawa, Ontario; Canada
6. Atmospheric and Environmental Research, Inc.; Lexington; Massachusetts; USA