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Studying the Spectral Characteristics of Electromagnetic Radiation Produced by Discharge between an Artificial Thundercloud and Ground

The results from experiments on studying the electromagnetic radiation produced by discharges between an artificial thundercloud and ground are presented. Five possible versions in which the main stage of discharge between an artificial thundercloud and ground evolves are revealed: upward flash, counter and downward flashes, including those with a radial streamer corona from the discharge channel. It has been found that the main stage versions of the discharge between an artificial thundercloud and ground that differ from one another in their formation conditions can manifest themselves also in the specific features of the electromagnetic radiation produced by the discharge (which is recorded by wide-band aerials) and its spectrum. A wavelet analysis was carried out, which made it possible to determine the specific features pertinent to the spectral characteristics of the electromagnetic radiation produced by the identified discharge versions and the current impulse parameters at the discharge main stage. It has been found that relatively small values of the current impulse amplitude and steepness are typical for upward flashes, which on the other hand are characterized by ultrahigh limit frequencies in their electromagnetic radiation wavelet spectrum. The highest electromagnetic radiation wavelet spectrum intensity is observed for downward flashes. It has been found that the radial streamer corona from the discharge channel parts and/or the interaction between the upward and downward leaders may lead to higher values of the discharge current impulse amplitude and steepness, and to higher characteristics of the discharge electromagnetic radiation wavelet spectrum. It is pointed out that the presence of frequency bands with a width from tens to hundreds of MHz in the electromagnetic radiation wavelet spectrum of discharges between an artificial thundercloud and ground should be taken into account in the design and operation of lightning direction finding systems.