1. Geophysical Institute University of Alaska Fairbanks Fairbanks Alaska USA
2. Now at NASA Goddard Space Flight Center Greenbelt Maryland USA
3. Institute of Space Physics and Applied Technology School of Earth and Space Sciences Peking University Beijing China
4. University of Toulouse, UPS‐OMP, IRAP Toulouse France
5. CNRS IRAP Toulouse France
6. Institute for Geophysics and Extraterrestrial Physics Braunschweig Germany