Piotr Baranski

Comparison of the charge moment change calculated from electrostatic analysis and from ELF radio observations

We compare the results of two methods of calculation of the charge moment change (CMC, also called the dipole moment change) of the cloud-to-ground lightning discharges. The first method uses multistation ground-based measurements of the E field change for the purpose of the lightning flash location and charge analysis. Our six stations, called the Local Lightning Detection Network (LLDN), were set up in the Warsaw region. The second method is based on measurements of the horizontal magnetic field component of electromagnetic waves generated by atmospheric discharges in the ELF (extremely low frequency) range. Our ELF station is equipped with two magnetic antennas, east-west and north-south and is located in a sparsely populated area of the Bieszczady Mountains in Poland (49.19°N, 22.55°E). We present and discuss the results obtained by both methods, focusing on the negative return stroke (RS) and the return stroke with continuing current (RS and CC) lightning discharges. Results show a good correlation between the CMC obtained by the two methods. For the negative RS and CC and RS the correlation coefficient is equal to +0.50 and +0.80, respectively.

Power spectrum density analysis of intra-cloud lightning discharge components from electric field recordings in Poland

The aim of this paper was to show usefulness of Power Spectrum Density analysis for identification of different components of IC lightning. We have presented some exemplary pulse train electric field recordings characterized for the specific time development of intra-cloud lightning discharges observed during summer thunderstorms in Poland. These data were gathered by two detection stations working independently in Warsaw and Rzeszow. Both stations are based on triggered electric field acquisition in the ELF-MF frequency range. Such recorded electric field courses of intra-cloud lightning were then analyzed both in the time domain and in the time-frequency domain with application of the short-time Fourier transform (STFT). On the basis of the used STFT procedure the Power Spectrum Density (PSD) spectrograms were computed. This whole computer procedure was performed by using the Matlab platform. Due to that we were able to distinguish some different intra-cloud lightning components as the preliminary breakdown stages including sequences of initial pulse bursts, K- and J-type electric field changes and sometimes even a trace of the Narrow Bipolar Pulses (NBPs). We have obtained different shape/pattern of the particular PSD stripes related/corresponding to the considered components of intra-cloud lightning. Summarizing of our PSD analysis of the recorded intra-cloud lightning incidents we have noticed that the PSD stripe structure of the initial breakdown processes for in-cloud and cloud-to-ground lightning is similar. But, the characteristic and different shape of the PSD stripe was obtained for the K-type electric field changes occurring during intra-cloud lightning. For these cases the PSD stripes were of the same height and width as for the return stroke incidents from the cloud-to-ground flash, but their intensity for the frequencies above 500 Hz was much lower. On the other hand, the PSD stripe obtained for the NBP was very often the strongest one and therefore it was hard to be properly distinguished in contrast to the return stroke stage from the cloud-to-ground flash.

Evaluation of multiple ground flash charge structure from electric field measurements using the local Lightning Detection Network in region of Warsaw

During three summer months, i. e., from 16 June 2009 to 16 September 2009 the Local Lightning Detection Network (LLDN) set up in the Warsaw region was successfully operated. For this period it was able to distinguish 16 events of multiple cloud-to-ground (CG) lightning flashes recorded simultaneously by all six stations, which recorded E field changes caused by the same flash. Using special software packet developed for purpose of E field analysis of recorded E field changes gave a new possibility to calculate three dimensional location of each point electric charge source, i.e., by the estimated value of its parameters x, y, z in local set of the Cartesian coordinates, and also the magnitude of the electric charge, Q, involved in particular return stroke or continuing current of the considered CG lightning discharge. Some examples of such spatial and time development of recorded multiple CG flashes initiated in different meteorological situation/thunderclouds are presented and discussed in the paper.