Electric fields of initial breakdown in positive ground flash

Abstract

Abstract. Pulse trains superimposed on the initial part of the electric field change of positive ground flashes are investigated. The characteristics of these pulse trains are found to be different from those of negative ground flashes and cloud flashes. Each pulse included in a pulse train appears as a bipolar waveform with pulse width from 5 to 52 •s and a mean of 18 •s. The time intervals between successive pulses are 10 to 180 •s with a mean of 54 •s. For each bipolar pulse, the ratio of the peak amplitude of the initial polarity to the maximum overshoot amplitude ranges from 0.4 to 4.7 with a mean value of 1.3. The ratio of maximum peak amplitude of successive pulses to the amplitude of the following return-stroke peak ranges from 0.02 to 1.9 with a mean of 0.27. IntroductionThe initial breakdown process in a lightning discharge is a precursor to both ground and cloud flashes. This process has been studied from the early days of lightning research. For negative cloud-to-ground lightning, according to Beasley et al. [1982], the electric field change prior to the first return stroke in a negative cloud-to-ground flash has two portions: the first they term "preliminary variations" which has a duration of about 90 ms and the second " InstrumentationOur study is primarily concerned with the initial breakdown process in positive cloud-to-ground lightning flashes. Electric field waveforms associated with lightning discharges have been recorded at three sites in the Hokuriku district area by using, a "wideband slow antenna" having frequency ranges from 0.2 Hz to 0.5 MHz. The system used in this study is similar to the system described by Brook et al.

Characteristics of Cloud-to-Ground Lightning in Chinese Inland Plateau.

“…Because of the complexity of the problem we have discussed these processes in another paper (Qie et al 2000b). Ushio et al (1998) analyzed the preliminary breakdown processes of positive CG flash in winter thunderstorms, and found that the mean time interval between successive preliminary breakdown pulses is 54.2 ms and the total duration of the pulses is 18.8 ms which is shorter than the value obtained in our study. Weidman and Krider (1978) found that the mean time interval between the successive preliminary breakdown pulses for summer thunderstorm is 130.0 ms and the total duration of the preliminary breakdown pulses is 41.0 ms.…”

O bserved Electric Field Changes o f Positive Lightning Flashes Preceded b y Preliminary Breakdown i n Padang

“…From Table 1 it can be seen that the number of positive CGs was 0.68% (77) of all lightning events during the 31 thunderstorm days. Several researchers have reported that the electric field changes of positive CG flashes are preceded by a PB process in the cloud that lasts about 12-200 ms on average [7,9,17,18]. It was found that all positive CG flashes were preceded by a PB pulse that was the same as in negative CG flashes, as reported previously by Hazmi et al [19].…”

“…It was found that all positive CG flashes were preceded by a PB pulse that was the same as in negative CG flashes, as reported previously by Hazmi et al [19]. The very initial polarity of the PB pulse train is usually unipolar and sometimes opposite to that of the following RS pulse [7,9]. A typical PB pulse train is shown in Figure 2.…”

“…In Table 1 respectively [7,9,10,11,17]. Our AM pulse duration was slightly longer than in the previous studies.…”

“…The electric field produced by the PB process in positive ground flashes is not the same as that of negative ground flashes. It has been found that in positive ground flashes, the initial pulse polarity of the electric field that is preceded by the PB process is sometimes different from that of the following RS [6][7][8][9][10]. The initiating mechanism of the positive lightning discharge remains a mystery because the charge structure of thunderclouds that create positive lightning is more complex than in the case of negative lightning [1,2,11,12].…”