Lightning attachment processes of three natural lightning discharges

Wang, D.; Takagi, Nobuyuki; Gamerota, W. R.; Uman, M. A.; Jordan, D. M.

doi:10.1002/2015jd023734

Cited by 33 publications

(21 citation statements)

References 20 publications

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“…Wang et al . [, , ] and Carvalho et al . [, ] have described similar variations in the risetime and amplitude of the luminosity in the lowest 60 m of RS channels.…”

Section: Discussionmentioning

confidence: 57%

“…Olsen et al [2004] report events where the RS speed had a nonmonotonic behavior with height, i.e., it first increased and then decreased, and there was also significant attenuation and dispersion of the luminous front as the RS propagated upward. Wang et al [2013Wang et al [ , 2014Wang et al [ , 2015 and Carvalho et al [2015Carvalho et al [ , 2017 have described similar variations in the risetime and amplitude of the luminosity in the lowest 60 m of RS channels. Wang et al [2013Wang et al [ , 2016 have reported that the initiation heights of RS above the ground termination vary from about 7 to 21 m in RTL and appear to be correlated with the amplitude of the peak current in the RS that follows.…”

Section: Resultsmentioning

confidence: 69%

“…The broadband optical radiation emitted by return strokes (RS) in rocket-triggered lightning (RTL) has been studied extensively to determine how the luminosity (W/m) (power per unit length emitted by the source) of the channel varies with height and time [Wang et al, 1999a[Wang et al, , 1999b[Wang et al, , 2013Winn et al, 2012;Carvalho et al, 2014Carvalho et al, , 2015Carvalho et al, , 2017, to measure propagation speeds of RS [Mach and Rust, 1989;Wang et al, 1995Wang et al, , 1999bWang et al, , 2000Wang et al, , 2013Wang et al, , 2014Wang et al, , 2015Chen et al, 2003;Olsen et al, 2004;Carvalho et al, 2015], and to determine how the optical output relates to the actual or inferred current at the channel base [Idone and Orville, 1985;Wang et al, 2005Wang et al, , 2013Wang et al, , 2014Qie et al, 2011;Carvalho et al, 2014Carvalho et al, , 2015. Here we describe calibrated measurements of the irradiance waveforms (W/m 2 ) (power per unit area incident onto the detector) that were produced by RTL RS at a known distance in the visible and near-infrared (VNIR) spectral region (0.4 to 1.0 μm).…”

Section: Introductionmentioning

confidence: 99%

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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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“…Wang et al . [, , ] and Carvalho et al . [, ] have described similar variations in the risetime and amplitude of the luminosity in the lowest 60 m of RS channels.…”

Section: Discussionmentioning

confidence: 57%

Section: Resultsmentioning

confidence: 69%

Section: Introductionmentioning

confidence: 99%

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

Quick

Krider

2017

JGR Atmospheres

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“…Note that this picture is quite different from that described by Wang et al . [] of a bifurcated channel, with terminations spaced by a few microseconds.…”

Section: Introducing the Rare Lightning Eventmentioning

confidence: 99%

Unusual features of negative leaders' development in natural lightning, according to simultaneous records of current, electric field, luminosity, and high‐speed video

et al. 2017

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The development of downward and upward leaders that formed two negative cloud‐to‐ground return strokes in natural lightning, spaced only about 200 µs apart and terminating on ground only a few hundred meters away, was monitored at Morro do Cachimbo Station, Brazil. The simultaneous records of current, close electric field, relative luminosity, and corresponding high‐speed video frames (sampling rate of 20,000 frames per second) reveal that the initiation of the first return stroke interfered in the development of the second negative leader, leading it to an apparent continuous development before the attachment, without stepping, and at a regular two‐dimensional speed. Based on the experimental data, the formation processes of the two return strokes are discussed, and plausible interpretations for their development are provided.

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“…We caution the reader that the velocities computed at the channel‐bottom may be affected by the unresolved bidirectional propagation of the return stroke wave. Our experimental setup was not designed to decompose these two waves propagating bidirectionally from their initiation height, but such decomposition has been done for both natural and triggered lightning [e.g., Wang et al ., , ]. We note that both cases with the time domain velocities greater than the speed of light were observed for the events triggered on or after 13 August 2014, when the photodiodes aimed at the channel‐bottom where separated by only 12 m, less than the lowest channel section separation of 28 m before 13 August 2014.…”

Section: Discussionmentioning

confidence: 81%

Frequency domain analysis of triggered lightning return stroke luminosity velocity

et al. 2017

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Fourier analysis is applied to time domain return stroke luminosity signals to calculate the phase and group velocities and the amplitude of the luminosity signals as a function of frequency measured between 4 m and 115 m during 12 triggered lightning strokes. We show that pairs of time domain luminosity signals measured at different heights can be interpreted as the input and the output of a system whose frequency domain transfer function can be determined from the measured time domain signals. From the frequency domain transfer function phase we find the phase and group velocities, and luminosity amplitude as a function of triggered lightning channel height and signal frequency ranging from 50 kHz to 300 kHz. We show that higher‐frequency luminosity components propagate faster than the lower frequency components and that higher‐frequency luminosity components attenuate more rapidly than lower frequency components. Finally, we calculate time domain return stroke velocities as a function of channel height using two time delay techniques: (1) measurement at the 20% amplitude level and (2) cross correlation.

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Lightning attachment processes of three natural lightning discharges

Cited by 33 publications

References 20 publications

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

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

Unusual features of negative leaders' development in natural lightning, according to simultaneous records of current, electric field, luminosity, and high‐speed video

Frequency domain analysis of triggered lightning return stroke luminosity velocity

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