1. Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens, 11810 Athens, Greece
2. Laboratory of Atmospheric Physics, Aristotle University of Thessaloniki, 54636 Thessaloniki, Greece
3. Research Centre for Atmospheric Physics and Climatology, Academy of Athens, 10680 Athens, Greece
4. Royal Netherlands Meteorological Institute (KNMI), 3731 De Bilt, The Netherlands
5. Deutscher Wetterdienst (DWD), 63067 Offenbach, Germany
6. European Space Agency, 00044 Frascati, Italy
7. Leibniz Institute for Tropospheric Research (TROPOS), 04318 Leipzig, Germany