The Four Possible Waves in Ionized Gas in a Magnetic Field

Abstract

ACCORDING to the magneto-ionic theory of Appleton1 and others, two distinct radio waves may be propagated through ionized gas permeated by a magnetic field. More recently, three hydromagnetic waves have been found for the same medium2,3. A ‘plasma’ or electron sound wave has long been known, but only investigated for the relatively simple cases of zero magnetic field4,5 or propagation across the magnetic field6. Finally, sound waves must be capable of propagation in the magneto-ionic medium. These numerous waves have been discovered from diverse approaches, and the connexion between them, if any, is not clear.