F layer reflections and ion effects in the propagation of terrestrial ELF waves

At night, ELF waves penetrate above the D layer, and propagation parameters of the earth to ionosphere wave guide are dependent on the detailed ionospheric structure below the F layer. The propagation characteristics are dependent on the altitude of the F layer, the electron density below this layer, the magnitude of the radial geomagnetic field component, and also on ions that tend to increase the absorption of the penetrating magneto-ionic mode. The propagation parameters of individual ionosphere models appear to be too erratic to explain long distance or global wave propagation, but the average of the propagation parameters derived for a number of different propagation geometries becomes comparable to the parameters deduced from a simpler isotropic ionosphere model, where waves are confined to altitudes below 100 km.