1. Radiophysics Department, Lobachevsky State University of Nizhny Novgorod, Nizhny Novgorod 603950, Russia
2. Department of Nonlinear Geophysical Processes, Institute of Applied Physics, Nizhny Novgorod 603950, Russia
3. Department of Applied Mathematics, Nizhny Novgorod Technical University, Nizhny Novgorod 603950, Russia