Pulse trains that are characteristic of preliminary breakdown in cloud-to-ground lightning but are not followed by return stroke pulses

In this study, we identify and examine electric field pulse trains that are characteristic of preliminary breakdown in negative cloud-to-ground discharges but are not followed by return stroke waveforms. We assume that such trains are manifestations of the initiation of downward negative stepped leaders that fail to propagate all the way to the ground and refer to these events as '' attempted first cloud-to-ground leaders,'' although some of them were followed by full-fledged cloud discharges. We examined a total of 2475 electric field records of lightning events acquired in Gainesville, Florida, in 2006, and waveforms in 33 of them were found to satisfy criteria set for attempted cloud-to-ground leaders. In addition to pronounced bipolar pulses with positive ( atmospheric electricity sign convention) initial half cycle, negative unipolar and negative ( initial half cycle) bipolar pulses were sometimes seen toward the end of the train. We also observed that at the beginning and at the end of the pulse train, there were narrower pulses, often having durations in the range of 1-2 mu s, which are more than an order of magnitude shorter than for '' classical'' preliminary breakdown pulses. The arithmetic mean of total pulse train durations is 2.7 ms, and the weighted arithmetic means of individual pulse durations and interpulse intervals are 17 and 73 ms, respectively. Some of the attempted cloud-to-ground leaders, which should belong to the cloud discharge category, can be misclassified as negative cloud-to-ground discharges by lightning locating systems such as the U. S. National Lightning Detection Network.