1. Department of Physics and Astronomy University of Louisville Louisville Kentucky USA
2. Now at Department of Physics and Astronomy Clemson University Clemson South Carolina USA
3. Centre for Research in Earth and Space Science York University Toronto Ontario Canada
4. Department of Physics University of New Brunswick Fredericton New Brunswick Canada
5. School of Electronic Information Wuhan University Wuhan China
6. Atmospheric and Planetary Sciences Hampton University Hampton Virginia USA
7. ESSIC University of Maryland College Park Maryland USA