1. Department of Physics University of Oslo Oslo Norway
2. Now at Technical University of Denmark Kongens Lyngby Denmark
3. Swedish Institute of Space Physics (IRFU)
4. Institute for Geophysics and Extraterrestrial Physics Technical University of Braunschweig
5. Department of Space and Plasma Physics, School of Electrical Engineering KTH Royal Institute of Technology Stockholm Sweden
6. Royal Belgian Institute for Space Aeronomy (BIRA‐IASB) Brussels Belgium
7. Department of Physics Umeå University Umeå Sweden
8. Laboratoire de Physique et de Chimie de l'Environnement et de l'Espace (LPC2E) Orléans France