1. Mullard Space Science Laboratory, Department of Space and Climate Physics University College London Dorking UK
2. Department of Physics National and Kapodistrian University of Athens, Panepistimioupolis Zografos Athens Greece
3. Goddard Space Flight Center National Aeronautics and Space Administration Greenbelt MD USA
4. Department of Physics University of Alberta Edmonton Alberta Canada
5. Institute of Astronomy, Astrophysics, Space Applications and Remote Sensing National Observatory of Athens Penteli Greece