The initial stage of cloud lightning imaged in high-resolution

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

doi:10.1002/essoar.10503153.1

Cited by 9 publications

(24 citation statements)

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“…Both of these flashes were imaged using a new algorithm that is improved over the one used in Hare et al (2019), as it is significantly faster and locates around three times more sources. This new algorithm was inspired by Kalman-filters and is described in Scholten et al (2020). Figure 2 shows two needles, one from each flash, that show the general characteristics of needles.…”

Section: Datamentioning

confidence: 99%

Needle Propagation and Twinkling Characteristics

et al. 2021

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Needles are a very recently discovered lightning phenomenon, described in Hare et al. (2019), that occur along positive leader channels. They appear like small leader branches, at most around 100-m long, and stick out from the channel. However, unlike leader branches, they exhibit ionization fronts that propagate up each needle, away from the positive leader channel. Hare et al. (2019) referred to these fronts as twinkles, and they occur at a very regular rate, around once per 5 ms. Pu and Cummer (2019) confirmed these findings, and showed that there is a location on the positive leader channel that moves forward along the positive at a regular speed (≈10 5 m/s), where there is no needle activity ahead of this point, and copious needle activity behind it. We call this point the needle production head (since it is the tip of where needles are produced), and we discuss it in more detail in Section 2.5. Paradoxically, despite propagating away from the positive leader channel, Hare et al. (2019) concluded that since needles emit copious VHF while positive leaders do not (Edens et al., 2012; Hare et al., 2019; Shao et al., 1999), needle twinkles must thus be a form of negative propagation. Pu and Cummer (2019) confirmed this by showing that the negatively charged end of a bidirectional leader suppressed needle activity, and by showing a needle that extended into a full negative leader. Saba et al. (2020) was able to observe optical emissions from needles on upward positive leaders. Saba et al. (2020) showed that these needles observed in optical had very similar properties to those reported in Hare et al. (2019) and Pu and Cummer (2019), including that they twinkled multiple times with a few milliseconds between twinkles without growing in length. However, the needles observed by Saba Abstract Recently, a new lightning phenomena, termed needles, has been observed in both VHF and in optical along positive lightning leaders. They appear as small (<100 m) leader branches that undergo dielectric breakdown at regular intervals (called twinkles). Providing a coherent and consistent explanation for this phenomenon is challenging as each twinkle is a form of negative breakdown that propagates away from the positive leader. In this study, we provide detailed observations of needles in VHF, observed during two lightning flashes. We show distributions of different needle properties, including twinkle propagation speeds, time between twinkles, and needle lengths, among others. We show a return stroke and multiple recoil leaders that quench needle activity. We also show that nearby needle activity does not seem to correlate together, and that needle twinkling can slow down by 10%-30% per twinkle. We conclude by presenting possibilities for how the positive leader could induce negative propagation away from the positive channel, and we argue that twinkles can propagate like a stepped leader or like a recoil leader depending on the temperature of the needle, which implies that needle twinkles can probably propagate without emitting ...

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Section: Datamentioning

confidence: 99%

Needle Propagation and Twinkling Characteristics

et al. 2021

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“…The heights of these charge layers have been inferred from the structure of the observed leaders. As discussed in [8,24] this initial leader has similar properties as those of a normal negative leader, however it propagates fast and quickly reaches a velocity of 10 6 m/s, as can be seen from the velocity plot in Fig. 3.…”

Section: Discussionmentioning

confidence: 54%

“…1. Since in [8] we have already shown the general structure of flash A, we focus here on the first 50 ms.…”

Section: Discussionmentioning

confidence: 99%

“…During this particular phase of leader propagation we observe the emission of a copious amount of VHF radiation as well as strong pulses in a broadband antenna, installed at a distance of less than 10 km from the LOFAR core to support lightning observations. In the work of [8] the IRNL mode was already observed, but it was thought that this propagation mode, called an initial leader in that work, was exclusive to the initial stage of lightning development. The fact that in [9] (see [10,11] for an overview of the extensive literature on initial leaders) the transition from the initial leader to a negative stepped leader has been observed with high-speed video and in electric field change data, supports the finding that initial leaders and IRNL's are the same.…”

Section: Introductionmentioning

confidence: 99%

“…In recent years radio observations of lightning has gone through some major developments, starting with lightning mapping arrays [18,19] on to VHF radio interferometers [20][21][22] and culminating in the precision observations using the LOFAR radio telescope operating in the 30 -80 MHz band [8,17]. These VHF observations are, however, not sensitive to currents at length scales of order 100 m and greater.…”

Section: Introductionmentioning

confidence: 99%

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A Distinct Negative Leader Propagation Mode

Scholten

Hare

Dwyer

et al. 2021

Preprint

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The common phenomenon of lightning still harbors many secrets such as what are the conditions for lightning initiation and what is driving the discharge to propagate over several tens of kilometers through the atmosphere forming conducting ionized channels called leaders. Since lightning is an electric discharge phenomenon, there are positively and negatively charged leaders. In this work we report on measurements made with the LOFAR radio telescope, an instrument primarily build for radio-astronomy observations. It is observed that a negative leader rather suddenly changes, for a few milliseconds, into a mode where it radiates 100 times more VHF power than typical negative leaders after which it spawns a large number of more typical negative leaders.This mode occurs during the initial stage, soon after initiation, of all lightning flashes we have mapped (about 25). For some flashes this mode occurs also well after initiation and we show one case where it is triggered twice, some 100 ms apart.We postulate that this is indicative of a small (order of 5 km2) high charge pocket.Lightning thus appears to be initiated exclusively in the vicinity of such a small but dense charge pocket.

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Needle Propagation and Twinkling Characteristics

Hare

Scholten

Dwyer

et al. 2020

Preprint

Self Cite

View full text Add to dashboard Cite

Needles are a very recently discovered lightning phenomenon, described in Hare et al. (2019), that occur along positive leader channels. They appear like small leader branches, at most around 100-m long, and stick out from the channel. However, unlike leader branches, they exhibit ionization fronts that propagate up each needle, away from the positive leader channel. Hare et al. (2019) referred to these fronts as twinkles, and they occur at a very regular rate, around once per 5 ms. Pu and Cummer (2019) confirmed these findings, and showed that there is a location on the positive leader channel that moves forward along the positive at a regular speed (≈10 5 m/s), where there is no needle activity ahead of this point, and copious needle activity behind it. We call this point the needle production head (since it is the tip of where needles are produced), and we discuss it in more detail in Section 2.5.Paradoxically, despite propagating away from the positive leader channel, Hare et al. (2019) concluded that since needles emit copious VHF while positive leaders do not (Edens et al., 2012;Hare et al., 2019;Shao et al., 1999), needle twinkles must thus be a form of negative propagation. Pu and Cummer (2019) confirmed this by showing that the negatively charged end of a bidirectional leader suppressed needle activity, and by showing a needle that extended into a full negative leader. Saba et al. (2020) was able to observe optical emissions from needles on upward positive leaders. Saba et al. (2020) showed that these needles observed in optical had very similar properties to those reported in Hare et al. (2019) and Pu and Cummer (2019), including that they twinkled multiple times with a few milliseconds between twinkles without growing in length. However, the needles observed by Saba Abstract Recently, a new lightning phenomena, termed needles, has been observed in both VHF and in optical along positive lightning leaders. They appear as small (<100 m) leader branches that undergo dielectric breakdown at regular intervals (called twinkles). Providing a coherent and consistent explanation for this phenomenon is challenging as each twinkle is a form of negative breakdown that propagates away from the positive leader. In this study, we provide detailed observations of needles in VHF, observed during two lightning flashes. We show distributions of different needle properties, including twinkle propagation speeds, time between twinkles, and needle lengths, among others. We show a return stroke and multiple recoil leaders that quench needle activity. We also show that nearby needle activity does not seem to correlate together, and that needle twinkling can slow down by 10%-30% per twinkle. We conclude by presenting possibilities for how the positive leader could induce negative propagation away from the positive channel, and we argue that twinkles can propagate like a stepped leader or like a recoil leader depending on the temperature of the needle, which implies that needle twinkles can probably propagate without emitting VHF...

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The initial stage of cloud lightning imaged in high-resolution

Cited by 9 publications

References 28 publications

Needle Propagation and Twinkling Characteristics

Needle Propagation and Twinkling Characteristics

A Distinct Negative Leader Propagation Mode

Needle Propagation and Twinkling Characteristics

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