1. Swedish Institute of Space Physics; Uppsala Sweden
2. Institute of Geophysics and Planetary Physics; University of California; Los Angeles California USA
3. Institut für Geophysik und Extraterrestrische Physik; Braunschweig Germany
4. Space Sciences Laboratory; University of California; Berkeley California USA
5. Laboratoire de Physique des Plasmas; CNRS/Ecole Polytechnique/UPMC; Velizy France