1. Department of Space Physics, School of Electronic InformationWuhan University Wuhan China
2. Department of Mathematics and StatisticsMemorial University of Newfoundland St. Johns Newfoundland Canada
3. Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences Potsdam Germany
4. Institute of Physics and AstronomyUniversity of Potsdam Potsdam Germany
5. Department of Earth, Planetary, and Space SciencesUniversity of California Los Angeles California USA