1. Space Physics and Astronomy Unit University of Oulu Oulu Finland
2. Department of Physics of Earth, Faculty of Physics St. Petersburg State University St. Petersburg Russia
3. PMOD/WRC and IAC ETHZ Davos Dorf Switzerland
4. Western Department of Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Waves Propagation Russian Academy of Sciences Kaliningrad Russia
5. Sodankylä Geophysical Observatory University of Oulu Oulu Finland