The effect of the latitudinal variation of the terrestrial magnetic field strength on ion cyclotron whistlers

Abstract

The propagation of a low frequency electromagnetic wave in a cold multicomponent plasma in which collisions between electrons, ions and neutral particles can occur, is discussed. The wave frequencies are of the order of the ion gyro-frequencies. When the angle θ between the wave normal and the magnetic field exceeds a critical value θ c , then the sense of rotation of the electric and magnetic field vectors of the wave can suffer reversal. This phenomena is discussed for a model night-time ionosphere, and it is shown that the value of θ c , and the height at which reversal occurs, depend on frequency. An ion cyclotron whistler has three frequencies associated with it, namely the ion gyro-frequency at the satellite, the crossover frequency at the satellite and the cut-off frequency. The cut-off frequencey is the greatest frequency that has suffered polarisation reversal in traversing the lower ionosphere. The main purpose of the present paper is to determine the effect of the latitudinal variation of the terrestrial magnetic field on the cut-off frequency of proton whistlers. It is assumed that the wave normal is refracted to become vertical on entering the lower ionosphere so that θ is related to magnetic latitude φ. Also considered is the effect of the magnetic field strength variation on the high latitude cut-off of proton whistlers.