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Telecommunications and Radio Engineering
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ISSN Print: 0040-2508
ISSN Online: 1943-6009

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Telecommunications and Radio Engineering

DOI: 10.1615/TelecomRadEng.v51.i1.40
pages 25-34

Natural ELF Electromagnetic Pulses

Alexander P. Nikolaenko
Institute of Radio Physics and Electronics of the NASU, Kharkov, Ukraine


An interest towards monitoring the natural electromagnetic pulse radio signals re-appeared recently stimulated by the attempts of location the distant powerful lightning strokes that cause optical emissions in the upper atmosphere. Such a luminous structure over a thunderstorm cell may reach the 95 km altitude. Optical events were classified as 'red sprites', 'elves', and 'blue jets', see [1-3] and reference therein. The observations were performed over the USA territory, and the co-ordinates of causative strokes were established with the National Lightning Detection Network. To cover a wider territory, an application of the Schumann resonance frequency range had been suggested, namely, the frequencies from a few Hz to a hundred Hz [4]. The slow tail technique may be applied as well at the distances to a few thousands km, see [5] and reference therein. Slow tail atmospherics are observed at the frequencies from a few hundred to a few thousand Hz. Both the measurement techniques are not new, these were developed and used actively in 60s-70s. A zero order mode or TEM wave propagates in the Earth-ionosphere waveguide at the frequencies below 1.6-1.7 kHz. The first transverse resonance occurs at the above frequency [6], the particular value depends on the ambient day- or night-time propagation conditions.
The wave attenuation factor is small below the 100 Hz frequency, enabling a radio wave to travel around the Earth's circumference. The global or Shumann resonance (SR) is observed then. When the frequency increases, the wave absorption grows, and the 'round-the-world' waves become so small that the resonance vanish, and the spectra become smooth. This was one of a reasons why the Q-bursts in the SR range and the slow tail atmospherics that are observed at higher frequencies were treated separately.
The goal of the present study is an analysis of the model solution within the whole the extremely low frequency (ELF) band. We apply a well-known frequency domain solution for the wave travelling in the spherical Earth-ionosphere cavity. The time dependent field components are obtained with the numerical Fourier transform. Within such an approach, any further development of the known theory is unnecessary, and the field distribution over the frequency-distance plane are obtained from the unified positions.