Pasan Hettiarachchi

Experimental study of leader tortuosity and velocity in long rod-plane air discharges

Long air gap electrical discharges are of particular interest among scientists and engineers working on high voltage techniques and lightning research. In the present work we report experimental results obtained while testing a long rod-plane air gap with positive switching-like voltage impulses to study the velocity and tortuous progression of the leader discharge. Voltage and current waveforms were recorded. Two still digital cameras were used to track the leader tortuous path. By using a fast digital camera, the leader temporal evolution was recorded and its propagation velocity was estimated. Three angles were used to describe the leader tortuous progression.

On the possible origin of chaotic pulse trains in lightning flashes

It is suggested that the chaotic pulse trains observed in lightning flashes are created as a result of the superposition of several regular pulse bursts produced by dart leader type discharge processes in the cloud. The similarity between the individual pulses in both chaotic and regular pulse bursts strengthen this suggestion.

Some characteristics of leader pulses in positive cloud-to-ground flashes

Compared to negative ground flashes, not much is known about the characteristics of leaders in positive ground flashes. This paper presents some characteristics of the electric field pulses observed during leader propagation in positive ground flashes. We analyzed in detail the electric field changes produced by 50 positive ground flashes during 2014 summer thunderstorms in Uppsala, Sweden. Pronounced leader pulses were observed in 22% of the cases. They were observed to occur 1.4 ms or less before the first return stroke. Interpulse duration ranged from 13.3 - 50.3 μs with a mean value of 24.7 μs. The largest relative amplitude ranged from 2.7 - 17.8 % of the return stroke peak. No dependence of the pulses occurrence were observed with distance. However, the relative amplitude were found to decrease with distance. The presence of these pulses suggests that the leaders propagate in a stepped manner. One case of positive ground flashes preceded by negative polarity pulses just before the return stroke is also reported.

Preliminary observations of lightning signature at 2400 MHz in Sweden thunderstorm

This paper presents a preliminary observation of lightning signature at 2400 MHz. We believe this is the first time such observation was made in such frequency band. One positive ground discharge and one cloud discharge waveforms have been selected from a collection of waveforms recorded using fast and slow broadband antenna systems. In addition, waveforms recorded directly from 2400 MHz whip antenna associated with the selected ground and cloud discharges waveforms were observed. The measurements were carried out in Uppsala, Sweden in July 2012. We discovered a possible lightning signature at 2400 MHz with the existence of bursts of pulses happened to occur simultaneously with preliminary breakdown, negative return stroke and cloud pulses. These bursts of pulses possibly interfered in some ways with the transmitted bits leading to higher recorded error bits during the thunderstorm.