Simultaneously measured lightning return stroke channel‐base current and luminosity

Carvalho, F. L.; Jordan, D. M.; Uman, M. A.; Ngin, T.; Gamerota, W. R.; Pilkey, J. T.

doi:10.1002/2014gl062190

Cited by 26 publications

(36 citation statements)

References 17 publications

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“…Their Figure suggests that the decay in upward propagating luminosity for four dart‐stepped‐leader light pulses is exponential. An exponential decay constant of 22 m reduces the current amplitude to about 10% of its peak in 50 m, although the relationship between current and luminosity is not well understood [e.g., Liang et al , ; Carvalho et al , ]. Furthermore, the use of an exponential current decay allows a direct comparison between results here and those previously reported by Jerauld [] and Howard et al [].…”

Section: Discussionsupporting

confidence: 58%

“…It is interesting that the average speed of the upward luminosity measured by Wang et al [] for triggered lightning dart‐stepped leaders is 6.7 × 10 7 m/s and the luminosity speed for the lowest pulses is near 8 × 10 7 m/s, whereas the speed of the upward current we must assume to match the waveform is higher, 1.1 to 1.5 × 10 8 m/s. According to the theory of Liang et al [], with some experimental confirmation by Carvalho et al [], the upward speed of the current is expected to be greater than the corresponding speed of the luminosity. Perhaps we are providing additional evidence that this is the case.…”

Section: Summary and Discussionmentioning

confidence: 99%

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Estimation of triggered‐lightning dart‐stepped‐leader currents from close multiple‐station dE/dt pulse measurements

et al. 2015

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The modified transmission line model is used to derive the vertically propagating leader-step currents necessary to radiate measured dart-stepped-leader dE/dt pulses from triggered lightning at close range (<400 m) and low altitude (<70 m). The model-predicted dE/dt pulses were compared with measured dE/dt pulses at nine locations ranging from 27 to 391 m from the channel base for four dE/dt pulses radiated from two triggered dart-stepped leaders. The dE/dt pulses at the closest station, 27 m, were unipolar, dominated by electrostatic and induction components of the radiated dE/dt, and of opposite polarity to the more distant initial dE/dt peaks. The other, more distant, eight stations exhibited bipolar dE/dt pulses, being more or less dominated by the dE/dt radiation component. The derived leader-step current has a slow front that precedes a fast transition to peak amplitude followed by a slow decay to zero after several microseconds. For the four modeled dE/dt pulses, the estimated causative leader-step current peak amplitudes varied from 0.9 to 1.8 kA, the half-peak widths ranged from 370 to 560 ns, the charge transfers were about 1 mC, and the peak current derivatives were about 10 kA/μs. The upward propagation speeds of the leader-step current were from 1.1 to 1.5 × 10 8 m/s with exponential spatial current decay constants from 13 to 27 m. One dE/dt pulse is analyzed in more detail by studying changes in model-predicted waveforms versus current initiation altitude and by examining the effect of varying model input parameters.

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Section: Discussionsupporting

confidence: 58%

Section: Summary and Discussionmentioning

confidence: 99%

Estimation of triggered‐lightning dart‐stepped‐leader currents from close multiple‐station dE/dt pulse measurements

et al. 2015

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“…Recently, Carvalho et al . [, , ] have described measurements of the luminosity of very small (3.5 m) segments of channel starting 3 m above the ground termination, and they find a mean 10–90% optical risetime of 0.4 ± 0.1 us, that is only a factor of 2 less than the 0.8 ± 0.1 μs risetime that we measured in 2012 for a 62 m vertical length of channel. (The current risetimes were comparable in both experiments.)…”

Section: Discussionmentioning

confidence: 58%

Optical power and energy radiated by return strokes in rocket‐triggered lightning

Quick

Krider

2017

JGR Atmospheres

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The broadband optical radiation covering the visible and near‐infrared (VNIR) spectral regions (0.4–1.0 μm) has been measured from 70 negative return strokes (RS) in rocket‐triggered lightning; 17 events were recorded in 2011, and 53 were recorded in 2012. The radiometers were calibrated, and all measurements were time‐correlated with currents measured at the channel base. The risetime and peak of an irradiance waveform are determined primarily by the RS current and by the geometrical growth and total length of channel that is in the field of view of the sensor. Following an initial peak, the irradiance decays faster than the current until there is a plateau or secondary maximum 20 to 40 μs (median of 22 μs) after the peak current, a time when the current itself is steadily decreasing. Estimates of the space‐ and time‐average optical power per unit length (ℓo) that is emitted at the source during onset of RS have been computed using the measured slopes of 70 irradiance waveforms together with an assumption that the initial speed of propagation is 1.2 × 108 m/s. The values range from 0.25 to 9.5 MW/m, with a mean and standard deviation of 2.4 ± 1.7 MW/m, and they are in good agreement with prior estimates of ℓo that were made by Quick and Krider (2013) for the subsequent return strokes in natural lightning that reilluminate a preexisting channel. The values of ℓo also agree with numerical estimates of the VNIR power per unit length that were computed by Paxton et al. (1986). Estimates of the peak optical power per unit length (ℓR) that is radiated at the source have been derived from the peaks of 53 irradiance waveforms, and the values range from 0.4 to 11 MW/m with a mean and standard deviation of 4.2 ± 2.5 MW/m. Both ℓo and ℓR are approximately proportional to the square of the peak current at the channel base. Estimates of the total optical energy per unit length, Jo, that is radiated in the VNIR have been computed by integrating the irradiance waveforms over 2 ms. The values of Jo have a mean and standard deviation of 150 ± 140 J/m, and they are proportional to the total charge that is transported to ground in that interval.

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“…Zhou et al [] reported that M‐component and initial continuous current (ICC) pulses in triggered lightning having risetimes in the range of 10 µs to 100 µs for both current and luminosity at the ground exhibited a current‐to‐luminosity delay on the order of the current and luminosity risetimes. Thus, from Carvalho et al [] and Zhou et al [], it would appear that the observed delay between current and luminosity at the ground increases with both increasing current risetime and increasing luminosity risetime.…”

Section: Introductionmentioning

confidence: 99%

Lightning current and luminosity at and above channel bottom for return strokes and M‐components

Carvalho

Uman

Jordan

et al. 2015

J. Geophys. Res. Atmos.

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We measured current and luminosity at the channel bottom of 12 triggered lightning discharges including 44 return strokes, 23 M‐components, and 1 initial continuous current pulse. Combined current and luminosity data for impulse currents span a 10–90% risetime range from 0.15 to 192 µs. Current risetime and luminosity risetime at the channel bottom are roughly linearly correlated (τr,I = 0.71τr,L1.08). We observed a time delay between current and the resultant luminosity at the channel bottom, both measured at 20% of peak amplitude, that is approximately linearly related to both the luminosity 10–90% risetime (Δt20,b = 0.24τr,L1.12) and the current 10–90% risetime (Δt20,b = 0.35τr,I1.03). At the channel bottom, the peak current is roughly proportional to the square root of the peak luminosity (IP = 21.89LP0.57) over the full range of current and luminosity risetimes. For two return strokes we provide measurements of stroke luminosity vs. time for 11 increasing heights to 115 m altitude. We assume that measurements above the channel bottom behave similarly to those at the bottom and find that (1) one return stroke current peak decayed at 115 m to about 47% of its peak value at channel bottom, while the luminosity peak at 115 m decayed to about 20%, and for the second stroke 38% and 12%, respectively; and (2) measured upward return stroke luminosity speeds of the two strokes of 1.10 × 108 and 9.7 × 107 ms−1 correspond to current speeds about 30% faster. These results represent the first determination of return stroke current speed and current peak value above ground derived from measured return stroke luminosity data.

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Simultaneously measured lightning return stroke channel‐base current and luminosity

Cited by 26 publications

References 17 publications

Estimation of triggered‐lightning dart‐stepped‐leader currents from close multiple‐station dE/dt pulse measurements

Estimation of triggered‐lightning dart‐stepped‐leader currents from close multiple‐station dE/dt pulse measurements

Optical power and energy radiated by return strokes in rocket‐triggered lightning

Lightning current and luminosity at and above channel bottom for return strokes and M‐components

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