EVALUATING PARAMETERS OF CONDUCTIVITY PROFILE OF THE LOWER IONOSPHERE BY TWEEK-ATMOSPHERICS

A method is investigated of determining the effective height of the Earth-ionosphere waveguide for the basic and higher types VLF modes and of the distance from the source of radiation − lightning stroke based on analysis of extremely low (ELF) and very low frequency (VLF) pulsed radio signals − the tweek-atmospherics (tweeks). The effective height of the waveguide as a function of frequency is used deduced from analysis of the multimode tweeks. It allows for determining parameters of the conductivity profile in the lower ionosphere. Waveforms of tweek atmospherics were simulated numerically in the framework of the Earth-ionosphere waveguide model having an exponential conductivity profile. The dynamic spectra of tweeks were used to single out and analyze the individual waveguide modes of the signal. The standard deviation in determining the effective height of the waveguide for different modes varies from 0.2 to 0.4 km, which allows estimating parameters of the exponential conductivity profile of the lower ionosphere occupying the typical interval pertinent to the ambient night conditions. The systematic and random errors in determining the distance to the lightning strokes were of 10−40 km and of20−80 km, corresponding to stroke distances ranging from 500 to 3000 km.