A.V. Popov - Dr.Sc. (Phys.-Math.), Head of Department, Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation (IZMIRAN) (Moscow, Troitsk). E-mail: popov@izmiran.ru I.V. Prokopovich - Post-graduate Student Junior Research Scientist, Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation (IZMIRAN) (Moscow, Troitsk). E-mail: prokop21@mail.ru