Abstract
Propagation effects on the narrow bipolar pulses (NBPs) or the radiation fields generated by compact cloud discharges as they propagate over finitely conducting ground are presented. The results were obtained using a sample of NBPs recorded with high time resolution from close thunderstorms in Sri Lanka. The results show that the peak amplitude and the temporal features such as the full width at half maximum (FWHM), zero-crossing time, and the time derivative of NBPs can be significantly distorted by propagation effects. For this reason, the study of peak amplitudes and temporal features of NBPs and the remote sensing of current parameters of compact cloud discharges should be conducted using NBPs recorded under conditions where the propagation effects are minimal.
Highlights
IntroductionThe knowledge concerning the characteristics of electromagnetic fields generated by lightning flashes is of importance in evaluating the interaction of these electromagnetic fields with electrical networks and in the remote sensing of lightning current parameters from the measured fields [1,2,3,4]
The knowledge concerning the characteristics of electromagnetic fields generated by lightning flashes is of importance in evaluating the interaction of these electromagnetic fields with electrical networks and in the remote sensing of lightning current parameters from the measured fields [1,2,3,4].electromagnetic fields generated by lightning flashes change their character as they propagate over the ground surface due to selective attenuation of the high frequency signals by finitely conducting ground
Depending on the distance of propagation and the conductivity of ground, the peak, the rise time, full width at half maximum (FWHM), zero-crossing time of the lightning generated electromagnetic fields and their time derivatives measured at a given distance from the lightning channel may deviate more or less depending on the conductivity from the values that would be present over perfectly conducting ground
Summary
The knowledge concerning the characteristics of electromagnetic fields generated by lightning flashes is of importance in evaluating the interaction of these electromagnetic fields with electrical networks and in the remote sensing of lightning current parameters from the measured fields [1,2,3,4]. Electromagnetic fields generated by lightning flashes change their character as they propagate over the ground surface due to selective attenuation of the high frequency signals by finitely conducting ground (i.e., propagation effects). Propagation effects are evaluated for both negative NBPs, positive NBPs, and derivatives of NBPs.NBPs. The results are are based onon negative positiveNBPs, NBPs, and 9 waveforms of measured. 29 positive and 9 waveforms of measured derivatives of NBPs. NBPs are discharges taking place in cloud the cloud derivatives of NBPs. NBPs areproduced produced by by electrical electrical discharges taking place in the the the theory developed by Cooray [6][6]. Totocalculate effectsonon pulses generated by cloud theory developed by Cooray calculatethe the propagation propagation effects pulses generated by cloud flashes will be TheThe atmospheric usedinindefining defining polarity ofpulses. Atmosphericsign signconvention convention isisused thethe polarity of the Preliminary results of this study, basedonly only on on 27 negative were reported previously by by Preliminary results of this study, based
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