Alfv\'en waves: To the 80th anniversary of discovery

TL;DR

This paper commemorates the 80th anniversary of Alfvén wave discovery, discussing their fundamental properties, their role in space physics, and describing two resonators in Earth's ionosphere and radiation belt.

Contribution

It provides a historical overview and theoretical description of Alfvén waves and introduces the concept of ionospheric and radiation belt resonators.

Findings

Existence of ionospheric Alfvén resonator confirmed by observations.

Theoretical justification of the Earth's radiation belt resonator.

Alfvén waves can carry energy and information over long distances.

Abstract

The paper is dedicated to the anniversary of the discovery of Alfv\'en waves. The concept of Alfv\'en waves has played an outstanding role in the formation and development of cosmical electrodynamics. A distinctive feature of Alfv\'en waves is that at each point in space the group velocity vector and the external magnetic field vector are collinear to each other. As a result, Alfv\'en waves can carry momentum, energy, and information over long distances. We briefly describe two Alfv\'en resonators, one of which is formed in the ionosphere, and the second presumably exists in the Earth's radiation belt. The existence of an ionospheric resonator is justified theoretically and confirmed by numerous observations. The second resonator is located between reflection points located high above the Earth symmetrically with respect to the plane of the geomagnetic equator. Keywords: Alfv\'en velocity, dispersion law, group velocity, geometric optics, heavy ions.