On the characteristics of some radiation fields from lightning and their possible origin in positive ground flashes

Abstract

Characteristics of some radiation field waveforms of lightning from thunderstorms Sweden are presented. The waveforms are distinctly different from previously published signatures from intracloud discharges. In general, they are similar to the radiation fields produced by return strokes in negative ground flashes except for the initial polarity, but several important differences are found in the detailed characteristics. The zero‐to‐peak rise times of these waveforms are found to be in the range 5–25 μs. The waveforms begin with an initial portion or front which rises slowly for 3–20 μs to about half of the field peak amplitude. The observed mean values of 13 μs and 9 μs of zero‐to‐peak rise time and front duration, respectively, of these waveforms are about twice the corresponding values observed for negative return strokes. The mean radiation field peak value, normalized to 100 km, for these waveforms is 2 times that for negative return strokes. Some waveforms were preceded by small‐amplitude pulses which are assumed to be produced by a leader process. The mean separation in time of these pulses is about 26 μs, which may be compared with 14 μs observed for negative return strokes. Another important feature is the presence of ‘slow tails’ in some of these waveforms, indicating the presence of long‐lasting currents in their sources. It is suggested that the sources of the observed waveforms are return strokes bringing down positive charge to earth.

On the Possible Origin of Chaotic Pulse Trains in Lightning Flashes

“…The wideband electric field was recorded by a calibrated flat plate antenna located 1.5 m above ground. The antenna system consisting of a parallel flat plate antenna together with an electronic buffer circuits for fast electric field measurements is identical to the ones used previously in the studies reported in references [7][8][9]. Moreover, a narrowband electric field (3 MHz) was also recorded.…”

Electric Field Signatures in Wideband, 3 MHz and 30 MHz of Negative Ground Flashes Pertinent to Swedish Thunderstorms

“…Three parallel flat plate antennas were employed to sense the wideband electric field and the radiation at 3 and 30 MHz, respectively. The antenna system consisting of a parallel flat plate antenna together with an electronic buffer circuits for fast electric field measurements is identical to the system used previously by [8,[13][14][15]. The parallel plate antenna for wideband measuring system was placed on the ground with physical height of 1.5 m, whereas the parallel plate antennas for narrowband (3 MHz and 30 MHz) measuring system were installed on the roof top of a van, about 3 m high from the ground.…”

Characteristics of downward leader in a positive cloud‐to‐ground lightning flash observed by high‐speed video camera and electric field changes

“…The time intervals between the 26 leader pulses in Figure 4b ranged from 3 ms to 31 ms with a mean value of about 17 ms. Hojo et al [1985] reported that stepping could be detected before the return stroke in 26-30% of positive CG flashes. Cooray and Lundquist [1982] reported that the time interval between step pulses was 26 ms for positive lightning in Sweden. Proctor [1997] observed positive stepped leaders in two out of 175 flashes in South Africa.…”