Keywords
intracloud discharges
PSD analysis and spectrograms
measurements of lightning electric field
lightning detection and location systems
Abstract
The main goal of our paper is to present some results of E-field recordings obtained from a new measuring site in Rzeszow in the summer of 2014 during lightning and thunderstorm activity the in the south-east of Poland. To record the lightning signatures in the E-field we have used a field mill with a rotating dipole - an E-field sensor to measure the electrostatic component of the field intensity variations in the frequency range from 0 to 10 Hz, and, in addition we used an electric flat plate antenna (E-field change meter) operated with the charge amplifier unit in the frequency range from 0.5 to 3 MHz. We have undertaken the post-processing analysis of the gathered E-field lightning data to distinguish different components of the lightning cloud-to-ground (CG) or intracloud strokes (IC) both in the time and time-frequency domain. For this purpose we have used the standard Matlab procedures and algorithms to evaluate the Short-Time Fourier Transform (STFT) and calculate the power spectrum density (PSD) for each of our lightning flash-related E-field record. In this way we can recognize different stages of a single or multiple CG flash evolution, such as the preliminary breakdown (PB), the return stroke (RS) or continuing current (CC) events. Some valuable results of our PSD analysis related to adequate and reliable discrimination of RS stages in multiple CG flashes are shown. We postulate that such PSD analysis could be implemented in discrimination algorithms used in the regional or global lightning detection and location systems, and enhancing their efficiency in the RS or CC stroke change determination. Another important part of the measuring equipment of lightning registration system in Rzeszow, including a fast digital video camera and additional digital photo camera working with own independent acoustic and optical lightning trigger, and a GPS unit, are also described. These devices can be used together with simultaneous E-field recordings for better determination and understanding of different stages of complex lightning discharge phenomena.
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