Abstract
Abstract. Characteristics of the electric fields produced by stepped and dart-stepped leaders 200 µs just prior to the return strokes during natural negative cloud-to-ground (CG) lightning discharges have been analyzed by using data from a broad-band slow antenna system with 0.08 µs time resolution in southeastern China. It has been found that the electric field changes between the last stepped leader and the first return stroke could be classified in three categories. The first type is characterized by a small pulse superimposed on the abrupt beginning of the return stroke, and accounts for 42% of all the cases. The second type accounts for 33.3% and is characterized by relatively smooth electric field changes between the last leader pulse and the following return stroke. The third type accounts for 24.7%, and is characterized by small pulses between the last recognizable leader pulse and the following return stroke. On the average, the time interval between the successive leader pulses prior to the first return strokes and subsequent return strokes was 15.8 µs and 9.4 µs, respectively. The distribution of time intervals between successive stepped leader pulses is quite similar to Gaussian distribution while that for dart-stepped leader pulses is more similar to a log-normal distribution. Other discharge features, such as the average time interval between the last leader step and the first return stroke peak, the ratio of the last leader pulse peak to that of the return stroke amplitude are also discussed in the paper.Key words. Meteology and atmospheric dynamics (atmospheric electricity; lightning) – Radio science (electromagnetic noise and interference)
Highlights
Most of the negative cloud-to-ground (CG) lightning discharges start with preliminary breakdown activities inside the cloud, the time duration of which varies from several milliseconds up to a few hundreds of milliseconds
It has been confirmed that the time interval of stepped leader pulses is between 5–20 μs, with a mean value of 15 μs by measuring the electromagnetic fields radiated by individual leader steps with microsecond and sub-microsecond resolu
We present the results on the characteristics of the stepped and dart-stepped leaders 200 μs before the first return stroke in natural negative CG lightning discharges with sub-microsecond resolution, to help the understanding of the related physical processes
Summary
Most of the negative cloud-to-ground (CG) lightning discharges start with preliminary breakdown activities inside the cloud, the time duration of which varies from several milliseconds up to a few hundreds of milliseconds. A stepped or initial leader starts to progress from cloud to ground. The stepped leader usually takes tens of milliseconds to reach the ground and initiates the first return stroke. In the 1940’s, stepped leaders and dart leaders were first studied photographically by Schonland and Collens (1934) They stated that all return strokes were induced by one of the three initial processes: stepped leader, dart leader and dart-stepped leader. These photographic measurements were supplemented by Clarence and Malan (1957), Krider (1974), Krider and Radda (1975). It has been confirmed that the time interval of stepped leader pulses is between 5–20 μs, with a mean value of 15 μs by measuring the electromagnetic fields radiated by individual leader steps with microsecond and sub-microsecond resolu-
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