Radiation field pulses associated with the initiation of positive cloud to ground lightning flashes (original) (raw)
2004, Journal of atmospheric and solar-terrestrial physics
Seventy one electric ÿeld pulse trains that occurred during millisecond-scale time intervals before positive cloud to ground lightning ashes were analysed. These pulses are bipolar in nature and somewhat similar in pulse characteristics to the breakdown pulses preceding negative cloud to ground lightning. However, in the case of these positive ashes, the pulse characteristics of the pulse trains are conÿned in a much wider range of values than those of the pulse trains associated with negative return strokes. The leading edge of the pulses of the most commonly observed pulse trains that precede positive return strokes are relatively smooth, thus, di erent from their counterparts associated with negative ashes, in which case a few narrow pulses are superimposed on the rising edge of the bipolar pulses. Considering the initial polarity of pulses, four types of bipolar pulse trains preceding positive return strokes were identiÿed. For each type of pulse trains, statistics of pulse characteristics were given. In contrast, in the case of negative ground ashes, the bipolar pulse trains were almost always composed of pulses of the same polarity as that of the succeeding return stroke. The possible causes of the observation of several types of pulse trains and the signiÿcantly diversiÿed pulse characteristics of the breakdown pulse trains of positive ashes were discussed. The frequency spectrum of the electric ÿelds of the most common type of pulse trains was compared with the spectrum of the breakdown pulses of negative ashes and those of negative return strokes. This spectrum of the preliminary breakdown pulse trains of positive ground ashes is comparable with that of the preliminary breakdown pulse trains of negative ground ashes.
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