Lightning attachment processes of an “anomalous” triggered lightning discharge

Abstract

Using a high-speed optical imaging system specifically designed for observing the lightning attachment process, we have documented the process for stepped, dart, and dart-stepped leaders in an anomalous rocket-triggered lightning flash that terminated on a 10 m grounded utility pole. The initiation of the first return stroke was found to occur at a height of 23 ± 3 m above the top of the utility pole and was associated with three "slow front" dE/dt pulses. A time of 1.5 μs later, a fast rise in luminosity at 18 ± 2 m was associated with a "fast transition" dE/dt pulse. The first return stroke propagated bidirectionally from its initiation height, as did subsequent return strokes from their initiation heights of 8 ± 1 m to 16 ± 2 m above the top of the utility pole. The initial upward speed of the first return stroke was 1.4 × 10 8 m/s, while its initial downward speed was 2.2 × 10 7 m/s. The channel bottom luminosity of the first return stroke rose more slowly to a two or more times larger amplitude than that of the subsequent stroke luminosities. In contrast, the National Lightning Detection Network-derived first-return-stroke peak current is smaller than that of the second and the third strokes, and our electric field records at 45 km show similar behavior for the initial field peaks of the first and subsequent strokes.

Lightning attachment process to common buildings

“…It is known that when the downward and the upward leaders connect, a bidirectional return stroke wave is launched from the junction point Jerauld et al, 2007;Wang et al, 1999Wang et al, , 2013Wang et al, , 2014. In case A and case B, if the luminosity of the images is properly adjusted, one can observe that a partial saturation of the image (indicating the location of the connection) starts very close to the position of the tip of the downward negative leader in the previous frame (Figures 4a and 4b and Figures 4d and 4e) and not close to the position of the positive upward leader in the previous frame.…”

Lightning attachment processes of three natural lightning discharges

“…As reported previously by Wang et al . [, , ], LAPOS employs a type of photodiode‐fiber optics array system specifically designed for observing the lightning attachment process. One major advantage of the system is that it has a wide horizontal view, about 5–10 times larger than its vertical view.…”

“…For a few return strokes, however, the propagation speeds appeared to be much lower. Particularly, for the first return stroke of an anomalous triggered lightning discharge [ Gamerota et al ., ], its downward speed was only 2.7 × 10 7 m/s [ Wang et al ., ]. As an extension of our previous publications, this paper reports on the attachment processes of three natural lightning discharges which struck on site at the International Center for Lightning Research and Testing (ICLRT) located in north central Florida on Camp Blanding, a military facility.…”

“…Previously, we have reported on the attachment process, particularly the return stroke initiation process of rocket‐and‐wire triggered lightning discharges observed using a high‐speed optical system specifically designed for studying the lightning attachment process, named LAPOS (Lightning Attachment Process Observation System) [ Wang et al ., , ]. All the return strokes contained in those triggered discharges initiated at a height above the lightning termination point and then propagated bidirectionally from that height.…”

X-ray Observations at Gaisberg Tower

“…Of course, it is possible that the down-coming dart leader is met by a connecting leader and if the connecting leader is very large, the tip of the dart leader would be located at a longer distance just before the return stroke. The results obtained from triggered lightning show that the connecting leaders in dart leaders are not more than a few meters in height [27,28]. However, in our case, the field enhancement caused by the tower may lead to longer connecting leaders.…”