1. Laboratory of Climatology and Atmospheric Environment, Department of Geology and Geoenvironment, National and Kapodistrian University of Athens, 15784 Athens, Greece
2. Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens (IAASARS/NOA), 15236 Athens, Greece
3. Research Centre for Atmospheric Physics and Climatology, Academy of Athens, 11521 Athens, Greece
4. Physikalisch Meteorologisches Observatorium Davos, World Radiation Center (PMOD/WRC), 7260 Davos, Switzerland