Yu.N. Cherkashin - Dr.Sc. (Phys.-Math.), Professor, Chief Research Scientist, Institute of Terrestrial Magnetism Ionosphere and Radio Wave Propagation named after N.V. Pushkov. E-mail: yu_ch@izmiran.ru V.E. Eremenko - Dr.Sc. (Phys.-Math.), Professor, Leading Research Scientist, Institute of Terrestrial Magnetism Ionosphere and Radio Wave Propagation named after N.V. Pushkov. E-mail: eremenko@izmiran.ru O.S. Chyumakov - Leading Engineer, Institute of Terrestrial Magnetism Ionosphere and Radio Wave Propagation named after N.V. Pushkov. E-mail: yu_ch@izmiran.ru