Institution: | a Astronomical Institute, 05960, Tatranská Lomnica, Slovak Republic b Institute of the Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, 142190, Troitsk, Russia c IFSI/CNR, Via del Fosso del Cavaliere 100, 00133 Roma, Italy and Raggi Cosmici, Dip. Fisica/UNIRomaTre, Via del Vasca Navale 84, 00146, Roma, Italy |