Experimental Study of Lightning-Induced Currents in a Buried Loop Conductor and a Grounded Vertical Conductor

Schoene, Jens; Uman, M. A.; Rakov, Vladimir A.; Jerauld, J.; Hanley, B.D.; Rambo, K. J.; Howard, Joseph; DeCarlo, B.A.

doi:10.1109/temc.2007.911927

Cited by 23 publications

(33 citation statements)

References 23 publications

(31 reference statements)

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“…This conclusion stems from the existence of such pulses long before the development of the upward leader (a few milliseconds before the return stroke). Induced unipolar pulses of current along a vertical grounded conductor have also been recorded by Schoene et al () before a nearby negative CG lightning.…”

Section: Preliminary Findings From the Experimental Data And Fundamenmentioning

confidence: 61%

Features of Upward Positive Leaders Initiated From Towers in Natural Cloud‐to‐Ground Lightning Based on Simultaneous High‐Speed Videos, Measured Currents, and Electric Fields

2017

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Original simultaneous records of currents, close electric field, and high‐speed videos of natural negative cloud‐to‐ground lightning striking the tower of Morro do Cachimbo Station are used to reveal typical features of upward positive leaders before the attachment, including their initiation and mode of propagation. According to the results, upward positive leaders initiate some hundreds of microseconds prior to the return stroke, while a continuous uprising current of about 4 A and superimposed pulses of a few tens amperes flow along the tower. Upon leader initiation, the electric field measured 50 m away from the tower at ground level is about 60 kV/m. The corresponding average field roughly estimated 0.5 m above the tower top is higher than 0.55 MV/m. As in laboratory experiments, the common propagation mode of upward positive leaders is developing continuously, without steps, from their initiation. Unlike downward negative leaders, upward positive leaders typically do not branch off, though they can bifurcate under the effect of a downward negative leader's secondary branch approaching their lateral surface. The upward positive leader's estimated average two‐dimensional propagation speed, in the range of 0.06 × 106 to 0.16 × 106 m/s, has the same order of magnitude as that of downward negative leaders. Apparently, the speed tends to increase just before attachment.

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Section: Preliminary Findings From the Experimental Data And Fundamenmentioning

confidence: 61%

Features of Upward Positive Leaders Initiated From Towers in Natural Cloud‐to‐Ground Lightning Based on Simultaneous High‐Speed Videos, Measured Currents, and Electric Fields

2017

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“…The wire remnants above 17 m, unlike the in‐tact wire, are still slightly luminous at the time of this current pulse. The current amplitude of this upward unconnected leader is the largest current for such a discharge measured at the ICLRT [ Schoene et al ., ; J . D .…”

Section: Resultsmentioning

confidence: 99%

An “anomalous” triggered lightning flash in Florida

et al. 2013

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[1] An "anomalous" rocket-and-wire triggered lightning flash, a flash whose leaders do not follow the triggering wire remnants to ground, is characterized via high-speed video images at 10 and 300 kilo-frames per second, still camera images, 66-72 MHz source locations from a Lightning Mapping Array, channel-base current, and electric field and electric field derivative (dE/dt) measurements. This is the first anomalous flash of about 410 classically triggered flashes in north-central Florida. The flash began with an upward positively charged leader (UPL) initiating from the tip of the upward-moving triggering wire about 280 m above ground level. All but the bottom 17 m of wire exploded (became luminous) 37.6 ms after UPL initiation. A stepped leader initiated, likely from the top of the wire remnants, 282 m above ground level about 1.3 ms after the wire explosion and propagated downward for 2.1 ms, attaching to the top of a grounded utility pole 117 m southwest of the launching facility. The line charge density on the stepped leader is estimated to be of the order of 10 À3 C m À1 . Contrary to previously reported "anomalous" flashes in France and New Mexico (roughly 16% and 31%, respectively, of their triggered flashes), in our event, there was not a tens of milliseconds current-zero period preceding the stepped leader, there was no observed downward dart leader in the UPL channel prior to the stepped leader to ground, and there was a failed attempt to reestablish current in the exploded-wire channel between the UPL and ground.

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“…There are apparently three types of positive leaders that occur in response to an approaching negative stepped leader and can exhibit fluctuations of current and luminosity induced by negative‐leader steps. Those include upward connecting leaders (e.g., Hill et al, ; Lalande et al, ; Saba et al, ; Visacro et al, ), unconnected (or attempted) upward leaders (e.g., Tran & Rakov, ; Schoene et al, ; Visacro et al, ), and UPLs in negative upward flashes initiated from tall objects due to a nearby positive cloud‐to‐ground or intracloud flash. In the positive sparks considered in the present paper, the observed abrupt elongation of positive leaders could not be interpreted as being induced by an approaching negative stepped leader, since there were no negative leaders in the gap at the time of abrupt elongation.…”

Section: Introductionmentioning

confidence: 99%

Abrupt Elongation (Stepping) of Negative and Positive Leaders Culminating in an Intense Corona Streamer Burst: Observations in Long Sparks and Implications for Lightning

et al. 2018

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Properties of positive and negative leaders developing in air gaps ranging from 4 to 10 m that were subjected to 100/7,500‐μs voltage impulses were examined using a two‐frame, high‐speed video camera with image enhancement. Abrupt extension (stepping) that culminated in a bright and structured corona streamer burst was observed for both negative (expected for the “classical” stepping process) and positive (expected for the so‐called restrike process) leaders. Selected high‐quality images of five negative and four positive leaders with pronounced corona streamer bursts are presented here. The morphology of corona streamer bursts was essentially independent of polarity. Streamer bursts exhibiting nearly spherical symmetry were observed. For the four positive leaders, the newly added channel sections (steps) were almost straight and had lengths ranging from about 50 to over 120 cm. For the five negative leaders, most of the steps were curved and their 2‐D lengths were some tens of centimeters. It is generally thought that positive leaders in both long sparks and lightning extend continuously or exhibit optically unresolvable steps whose length is comparable to the leader tip size (1 cm or less) and that for sparks only when the absolute humidity is relatively high (>10 g/m3 or so) or voltage rise time is relatively long (around 1 ms or more) can larger steps occur. In this study, both modes of propagation for different branches of the same positive leader were observed.

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Experimental Study of Lightning-Induced Currents in a Buried Loop Conductor and a Grounded Vertical Conductor

Abstract: Abstract-Currents

Cited by 23 publications

References 23 publications

Features of Upward Positive Leaders Initiated From Towers in Natural Cloud‐to‐Ground Lightning Based on Simultaneous High‐Speed Videos, Measured Currents, and Electric Fields

Features of Upward Positive Leaders Initiated From Towers in Natural Cloud‐to‐Ground Lightning Based on Simultaneous High‐Speed Videos, Measured Currents, and Electric Fields

An “anomalous” triggered lightning flash in Florida

Abrupt Elongation (Stepping) of Negative and Positive Leaders Culminating in an Intense Corona Streamer Burst: Observations in Long Sparks and Implications for Lightning

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