Impact of the Ionospheric Day–Night Non-Uniformity on the ELF Radio-Wave Propagation

Abstract

The real structure of the lower ionosphere should be taken into account when propagation of extremely low frequency (ELF) radio waves is modeled and the global electromagnetic (Schumann) resonance in the Earth–ionosphere cavity is studied. In the present work, we use a 2D telegraph equation (2DTE) to estimate the effect of the ionospheric day–night non-uniformity on the electromagnetic field amplitude at the Schumann-resonance and higher frequencies. The properties of the cavity are accounted for by using the full wave solution technique through conductivity profiles in the daytime and night-time conditions. Electromagnetic fields in the non-uniform cavity are found by using a 2DTE. Both the sharp terminator model and the model of a smooth day–night transition were considered. The main attention was focused on effects arising on 5000-km paths that are perpendicular or parallel to the solar terminator line. The data were computed for a series of frequencies. A comparison of the calculated data with observation results is also performed and an interpretation of the observed effects is given.