Affiliation: | 1. Institute of Astronomy, Bulgarian Academy of Sciences, 6000 Stara Zagora, P.O. Box 442, Bulgaria;2. Institute of Electronics, Bulgarian Academy of Sciences, 1784 Sofia, Tzarigradsko shosse 72, Bulgaria;3. Solar Terrestrial Influences Laboratory, Bulgarian Academy of Sciences, Branch Stara Zagora, P.O. Box 73, 6000 Stara Zagora, Bulgaria;4. Institute of Atmospheric Sciences and Climate, National Research Council, Bologna, Italy |