Characteristics of the Lightning Stepped-Leader Electromagnetic Pulses

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Some characteristics and statistics of the electromagnetic fields produced by stepped-leaders just before cloud-to-ground lightning return strokes are described. A transient data acquisition system was used together with electric and magnetic field measuring devices with frequency bandwidths of 200 Hz to 1.6 MHz and 270 Hz to 2.3 MHz, respectively. In this recording mode, approximately 100 μs before the signal triggering, the transient data acquisition system could be recorded at a sampling time of 100 ns. The time intervals between peaks of the last leader pulse and return stroke field were widely distributed over the range of 5–70 μs, and the mean was approximately 16.2 μs with a standard deviation of 8.8 and 14.8 μs with a standard deviation of 5.2 for the positive and negative polarities, respectively. When the stepped-leader approaches closely to the ground, the time interval between leader steps tended to decrease with time. The mean peak amplitude ratio of the last leader pulse to the lightning return stroke field was $0.17\pm 0.12$ for the positive electric fields and $0.18\pm 0.09$ for the negative electric fields. On average, the full widths at half maximum of the stepped-leader pulses were $1.31\pm 0.8$ μs for the positive polarity and $1.71\pm 1.12$ μs for the negative polarity. All results presented here are somewhat different from those observed at other measuring sites, because lightning return stroke fields depend on geographical and meteorological conditions.
2006-02-15

Characteristics of the Lightning Stepped-Leader Electromagnetic Pulses

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