The Initial Stage of Cloud Lightning Imaged in High‐Resolution

Scholten, Olaf; Hare, B. M.; Dwyer, J. R.; Sterpka, C.; Kolmašová, Ivana; Santolı́k, O.; Lán, Radek; Uhlíř, Luděk; Buitink, S.; Corstanje, A.; Falcke, H.; Huege, T.; Hörandel, J. R.; Krampah, G. K.; Mitra, P.; Mulrey, K.; Nelles, A.; Pandya, Hershal; Pel, Alex; Rachen, J. P.; Trinh, T. N. G.; Veen, S. ter; Thoudam, Satyendra; Winchen, T.

doi:10.1029/2020jd033126

Cited by 25 publications

(41 citation statements)

References 43 publications

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“…However, to us, such a connection faces a basic difficulty for our data: fast positive breakdown implies that the IE is an NBE (that is, the NBE is caused by fast positive breakdown), but only two of our five IC flashes initiated with an NBE. The recent work by Scholten et al (2021) using other detailed lightning mapping systems, along with more recent studies using broadband interferometry, may be better poised to place these results within the context of fast positive breakdown.…”

Section: Discussionmentioning

confidence: 99%

“…In typical IC flashes, successive IB clusters occur at successively higher altitudes (Marshall et al 2013(Marshall et al , 2019Shi et al 2019). Recent work by Scholten et al (2021) shows imaging data for two inverted-polarity IC flashes. (Unlike typical IC flashes, inverted polarity IC flashes are those in which the initiation and IB stage are like that of a normal negative CG flash in that they initiate in a positive electric field and the negative leader initially propagates downward.…”

Section: Introductionmentioning

confidence: 99%

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Ultra-high speed video observations of intracloud lightning flash initiation

Stolzenburg

Marshall

Bandara

et al. 2021

Meteorol Atmos Phys

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This study describes results from video observations of five intracloud flashes located ≤ 20 km from the camera and recorded with 6.1 µs exposure time and 6.66 µs frame intervals. Video data are supported with electric field change (E-change) and VHF measurements, with emphasis on the flash initiating event (IE) and initial breakdown (IB) stage. In four of the five flashes, the IE is accompanied by weak luminosity, ≤ 5% above background, lasting for 300–500 µs. Two of these four IEs were positive Narrow Bipolar Events (NBEs) with VHF powers of 43 and 990 W; these are the first (known) data showing visible light detected with a positive NBE. Two other IEs with weak luminosity had powers of 0.5 and 1 W, and the IE with no detected luminosity had a VHF power of 3 W. A typical IB cluster consists of several narrow pulses and one classic pulse in E-change data (along with many VHF pulses), and each example flash has 2–10 IB clusters in the first 5–50 ms. The luminosity of IB clusters was substantially greater than IE luminosity, ranging from 10 to 40% above background in four examples, while for one flash with 10 IB clusters, the luminosity range was 35–360% above background (average 190%). Luminosity durations of IB clusters were 520–1750 µs with average 1210 µs. For both IEs and IB clusters, increases in the detected luminosity were closely timed with substantial VHF emissions and decreased when VHF emissions weakened.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Ultra-high speed video observations of intracloud lightning flash initiation

Stolzenburg

Marshall

Bandara

et al. 2021

Meteorol Atmos Phys

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“…In many cases, the algorithm used is closer to a time-of-arrival technique where only the location of the peaks are extracted from the result of the cross-correlations (Rison et al, 2016;Stock et al, 2014). The LOFAR impulsive imager uses a similar technique to the time-of-arrival, but has the advantage of hundreds of antennas and large baselines (Scholten et al, 2021b). As a result, the impulsive imager achieves source densities of over 200 sources per millisecond (Scholten et al, 2021b).…”

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confidence: 99%

The Spontaneous Nature of Lightning Initiation Revealed

Sterpka

Dwyer

Liu

et al. 2021

Geophysical Research Letters

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The basic principle of radio interferometry is that radio signals measured by separate antennas from a single source add coherently when adjusted for propagation time delays, while pulses from different sources or from random noise add incoherently (Taylor et al., 1999). For a lightning source, the combined signals will result in a received power approximately proportional to the square of the number of antennas and inversely proportional to the square of the distance from each antenna to the source. In contrast, signals from random noise will result in received power approximately proportional to the number of antennas. LOFAR is comprised of thousands of VHF antennas that are distributed all over Europe. For lightning studies, antennas are selected from the Netherlands to provide both large and small antenna separations (also known as baselines). The combination of the low-noise antennas and long baselines provides outstanding image resolution due to the fact that the maximum achievable angular resolution is proportional to λ/d, where λ is the wavelength of the radiation and d is the largest baseline length. Interferometers previously used to study lightning typically consisted of 3-4 antennas separated by a few hundred meters resulting in a resolutions on the order of 1.6° azimuth and 3.5° in elevation with no sensitivity along the radial axis (Tilles et al., 2019). In many cases, the algorithm used is closer to a time-of-arrival technique where only the location of the peaks are extracted from the result of the cross-correlations (Rison et al., 2016;Stock et al., 2014). The LOFAR impulsive imager uses a similar technique to the time-of-arrival, but has the advantage of hundreds of antennas and large baselines (Scholten et al., 2021b). As a result, the impulsive imager achieves source densities of over 200 sources per millisecond (Scholten et al., 2021b). Within this work and the previous impulsive imager, we achieve angular resolutions up to 1 arc sec in azimuth and 2 arc sec in elevation. This results in submeter resolution along both the horizontal (azimuth) and elevation axes, while also achieving 5 m resolution along the radial axis. LOFAR beamforming combines hundreds of antennas and selects baselines of up to 100 km, resulting in images with remarkably high signal to noise ratios and resolutions

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“…First, by demonstrating the unique flexibility of the LOFAR instrument. At the moment LOFAR is operated in a triggered mode, to produce high-quality images of a few flashes (e.g., (Hare et al, 2019;Scholten et al, 2021)). However, this work suggests the possibility of operating LOFAR in a continuous LMA-like mode to capture every lightning flash in a storm with lower quality, which will be investigated in future work.…”

Section: Discussionmentioning

confidence: 99%