Radio Emission Reveals Inner Meter-Scale Structure of Negative Lightning Leader Steps

Hare, B. M.; Scholten, Olaf; Dwyer, J. R.; Ebert, Ute; Nijdam, S Sander; Bonardi, A.; Buitink, S.; Corstanje, A.; Falcke, H.; Huege, T.; Hörandel, J. R.; Krampah, G. K.; Mitra, P.; Mulrey, K.; Neijzen, B.; Nelles, A.; Pandya, Hershal; Rachen, J. P.; Rossetto, L.; Trinh, T. N. G.; Veen, S. ter; Winchen, T.

doi:10.1103/physrevlett.124.105101

Cited by 38 publications

(42 citation statements)

References 32 publications

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“…This is extremely similar to the VHF bursts we discussed in Hare et al. (2020), which we found along negative leaders, where we attributed the large peak at small time separation (<0.5 μs in Figure 16) to stepping. This implies that needles, at least sometimes, tend to step‐like negative leaders.…”

Section: Datasupporting

confidence: 91%

“…Furthermore, after the return stroke the needle production head jumps forward by 250 m, consistent with continuous silent propagation of the positive leader. Thus, under the assumption that the positive leader was propagating during the VHF silence after the return stroke, the VHF power density emitted by a positive leader, at about 10 km distant, must be less than our background noise power, which is dominated by the galactic background, at about 1 × 10 −12 W (Hare et al., 2020). Thus,

\frac{P_{L e m i t t e d}}{R^{2}} A < P_{G r e c i v e d},

where P Lemitted is the power emitted by the positive leader, R is the distance between the closest antenna and the positive leader (≈8 km), A is the effective area of our antennas (≈1 m 2 ), and P G recived is the received galactic background power.…”

Section: Discussionmentioning

confidence: 90%

Section: The Silence Of the Positive Leadersmentioning

confidence: 88%

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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: Datasupporting

confidence: 91%

\frac{P_{L e m i t t e d}}{R^{2}} A < P_{G r e c i v e d},

Section: Discussionmentioning

confidence: 90%

Section: The Silence Of the Positive Leadersmentioning

confidence: 88%

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Needle Propagation and Twinkling Characteristics

et al. 2021

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“…This is very close to the burst duration seen in Hare et al. (2020) where it is associated with negative leader stepping. However, the time between bursts of VHF power is about 0.1–0.15 ms which is longer than the 0.05 ms observed in Hare et al.…”

Section: The Initial Stages Of Dutch Lightning Flashessupporting

confidence: 87%

“…This is very close to the burst duration seen in Hare et al (2020) where it is associated with negative leader stepping. However, the time between bursts of VHF power is about 0.1-0.15 ms which is longer than the 0.05 ms observed in Hare et al (2020) for normal negative leader propagation. Negative leaders at heights between 2 and 4 km were analyzed and no dependence on altitude was observed over this range.…”

Section: 1029/2020jd033126supporting

confidence: 76%

The Initial Stage of Cloud Lightning Imaged in High‐Resolution

Scholten

Hare²,

Dwyer

et al. 2021

JGR Atmospheres

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The relationship of lightning radio pulse amplitudes and source altitudes as observed by LOFAR

Machado

Scholten

Hare

et al. 2021

Preprint

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A negative leader propagates in a stepping fashion where the leader halts in between forward jumps. In between the forward jumps the corona at the leader tip gradually charges up until the corona explodes forward in a corona burst, emitting strong very high frequency (VHF) pulses. A corona is a region of very weakly conducting plasma around a leader, generally thought to consist of many streamers where a streamer is a self-propagating structure which develops inside a charged region (Dwyer & Uman, 2014). It is thought that VHF (30-300 MHz) radio emission from lightning is dominated by streamer activity (

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Radio Emission Reveals Inner Meter-Scale Structure of Negative Lightning Leader Steps

Cited by 38 publications

References 32 publications

Needle Propagation and Twinkling Characteristics

Needle Propagation and Twinkling Characteristics

The Initial Stage of Cloud Lightning Imaged in High‐Resolution

The relationship of lightning radio pulse amplitudes and source altitudes as observed by LOFAR

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