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ISSN Druckformat: 0040-2508
ISSN Online: 1943-6009
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DEVIATIONS OF SOURCE BEARING IN THE EARTH–IONOSPHERE CAVITY WITH THE DAY–NIGHT NON-UNIFORMITY
ABSTRAKT
The Earth-ionosphere cavity is characterized by the day–night non-uniformity and impact of this non-uniformity on the field amplitude and its spectrum was addressed in literature. However, the modifications of arrival angle caused by this inhomogeneity were not considered. We obtain the source bearings in the framework of the smooth day–night transition. The source and the receiver are located on the zero meridian at points with coordinates 22.5° N and 22.5° S, respectively, while the propagation path 5 Mm long occupies two characteristic positions. One of them corresponds to 4 hr UT (the path lies in the night hemisphere) and the second one corresponds to 8 hr UT (the path is located at the day side of morning terminator). We use the full wave solution to determine the ELF propagation parameters. The field spectra are found using the 2D telegraph equations. The following results were obtained: terminator impact is absent when the center of propagation path coincides with the center of the night or the day hemisphere, it increases when the path approaches the day–night interface; the source bearing deviations reach ~3°; their frequency dependence is similar to Schumann resonance pattern; a weak elliptical polarization is observed for a monochromatic signal having the sign changing when the propagation path moves from the night to the dayside; temporal variations of horizontal magnetic field components and the Umov–Poynting vector have a cross-like shape obscuring determination of the source bearing; application of a Schumann resonance receiver alters the pulsed shape, but maximum angular deviations do not increase. Thus, impact of day–night non-uniformity on the source bearing in the Schumann resonance frequency band is comparable with natural fluctuations caused by the noise nature of the thunderstorm activity. Detection of the terminator effect is possible for exceptionally powerful ELF–transients.