A full-wave study of ion-cyclotron whistlers in the ionosphere

Abstract

A generalised multiple-reflection full-wave method has been used to study ioncyclotron whistlers in the ionosphere. At a frequency of 400 Hz about 25 per cent of the incident electron whistler energy below the ionosphere is available for ion whistler production at the crossover level for nearly all angles of incidence, the figure being reduced by a factor of 4 at 100 Hz. At the crossover level the same typical coupling pattern is obtained for widely varying wave and collision frequencies and altitudes. As a function of θ, the angle between the wave normal and the magnetic field direction, the R-mode flux drops to half-power near θ = 25°, where it equals that of the L mode, and drops to zero near θ = 40°, where the L mode peaks. The relation of θ to the critical coupling angle θ c, has negligible effect on the coupling pattern, which is determined primarily by ‘limiting polarization’ effects, stemming from the proximity of the R and L refractive indices for 0 ⩽ 0 ≲ 20°. There is negligible reflection or mode conversion at the gyrofrequency levels where the L mode is completely absorbed, and for high ionic collision frequencies there is appreciable absorption of the L mode above crossover, especially for large θ. At very low geomagnetic latitudes the proton gyrofrequency and crossover levels tend to merge, and for most frequencies only the electron whistler will be observed.