Ultralow Frequency Resonators: on the 80th Anniversary of the Discovery of Alfvén Waves

Abstract

The concept of Alfvén waves, introduced into science 80 years ago, played an important role in the formation and development of cosmic electrodynamics. Alfvén waves differ in that at each point in space the group velocity vector and the vector of the external magnetic field are collinear to each other, due to which the waves can carry momentum, energy, and information over long distances. In memory of the outstanding event, we briefly describe two Alfvén resonators, one of which is located high above the Earth, in the radiation belt, and the second, in the ionospheric layers. Both resonators have a discrete spectrum in the upper part of the range of ultralow frequency oscillations of natural origin (approximately from 0.2 Hz to 7 Hz). The close connection between the concept of Alfvén waves and the current problems of the electrodynamics of geophysical media is especially emphasized.