1. The Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA
2. IAASARS, Observatory of Athens, Penteli, Greece
3. Department of Physics, Section of Astro-geophysics, University of Ioannina, Ioannina, Greece
4. Goddard Planetary Heliophysics Institute, University of Maryland, Baltimore, MD, USA
5. NASA, Goddard Space Flight Center, Greenbelt, MD, USA