[1] Natl Observ Athens, Ionospher Grp, Athens, Greece
[2] Le Studium, Orleans, France
[3] Ctr Natl Rech Sci, Lab Planetol Grenoble, Grenoble, France
[4] Rhea Syst, Noordwijk, Netherlands
[5] Rutherford Appleton Lab, Space Environm Grp, Chilton, England
[6] Natl Inst Astrophys, Trieste, Italy
[7] Royal Observ Belgium, Brussels, Belgium
[8] Swedish Inst Space Phys, Lund Solar & Space Weather Grp, Lund, Sweden