Characterizing three types of negative narrow bipolar events in thunderstorms

Bandara, Sampath; Marshall, T. C.; Karunarathne, Sumedhe; Karunarathne, Nilmini; Siedlecki, Raymond; Stolzenburg, Maribeth

doi:10.1016/j.atmosres.2019.05.013

Cited by 21 publications

(48 citation statements)

References 22 publications

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“…About 70 μs later (51.75419 s), the first IB pulse occurs coincident with an obvious increase in the integrated intensity (in two frames) despite its small E‐change amplitude. The time between this initiating event and the first IB pulse is well within the range of values (20–150 μs, average 82.3 μs) found by Bandara et al () for 15 NNBE(H) cases. In the period between the initiating event and the first IB pulse (Figure ), there is another small, fast unipolar pulse; this pulse fits the character of a so‐called enhancing event during the IEC period, as described by Marshall et al (Marshall et al, ; ).…”

Section: Resultssupporting

confidence: 86%

“…Prior to the first large IB pulse, there are two events evident in the E‐change data that deserve special mention. The earliest activity detected in this flash is labeled “initiating event” (51.75412 s) in Figure : The small amplitude, unipolar E‐change waveform precisely resembles that described by Bandara et al (, see their Figure A.1) as a “hump‐type Negative Narrow Bipolar Event” or NNBE(H) and by Rison et al () as a “more monopolar” NNBE which those studies determined initiate some negative CG flashes. However, we have no VHF power data to compare and confirm the NNBE identification, and LDAR did not locate a coincident event.…”

Section: Resultssupporting

confidence: 71%

“…In this case, the first IB pulse with luminosity burst is about 285 m above the video camera frame (frame top altitude is 4.41 km). Despite the camera frame being slightly too low, there is weak luminosity scattered into the video image at the time of the initiating event in the E‐change data, which was a unipolar “hump‐type” weak negative NBE or NNBE (e.g., Bandara et al (). This is the first report we are aware of to show evidence of luminosity with an initiating event or an NBE.…”

Section: Discussionmentioning

confidence: 99%

“…Recent findings (e.g., Marshall et al, ) suggest that the earliest events in a flash seem to occur in the following order: an ionizing initiation event, followed by a slower charge motion (detected as an initial electric field change [called IEC]), followed by a series of initial breakdown (IB) pulses (collectively the IB stage of the flash), and followed by a stepped leader. The initiation event can be a narrow bipolar event with power > 1,000 W in the VHF band (e.g., Rison et al, ) or a much weaker event with VHF power < 1 W (e.g., Marshall et al, ); the weaker events are apparently more usual for initiations of both IC flashes (Lyu et al, ) and CG flashes (Bandara et al, ). Although the mechanism producing IB pulses is unknown, they are understood and modeled as short current surges and have a characteristic bipolar waveform when detected with electric field change (E‐change) sensors (e.g., Weidman & Krider, ).…”

Section: Introductionmentioning

confidence: 99%

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On the Transition From Initial Leader to Stepped Leader in Negative Cloud‐to‐Ground Lightning

2020

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High‐speed video and electric field change data are used to describe the first 5 ms of a negative cloud‐to‐ground flash. These observations reveal an evolution in character of the luminosity and electric field change pulses as two branches of the leader separately transition from initial leader to propagating as a negative stepped leader (SL). For the first time reported, there is evidence of weak luminosity coincident with the initiating event, a weak bipolar pulse 60 μs prior to the first initial breakdown (IB) pulse. During the IB stage, the initial leader advances intermittently at intervals of 100–280 μs, in separate light bursts that are bright for a few 20‐μs frames and are time coincident with IB pulses. In the intervals between IB pulses, the initial leader is dim or invisible during the earliest 1.8 ms. Within 2 ms, the leader propagation begins transitioning to an early SL phase, in which the leader tip advances at more regular intervals of 40–80 μs during relatively dim and brief steps which are coincident with SL pulses having short duration, small amplitude, and typically unipolar waveform. These data indicate that when the entire initial leader length behind the lower end begins to remain illuminated between bursts, the propagation mode changes from IB bursts to SL steps, and the IB stage ends. The results support a hypothesis that the early initial leader development occurs in the absence of a continuously hot channel, thus the initial leader propagation is physically unlike the self‐propagating SL advance.

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Section: Resultssupporting

confidence: 86%

Section: Resultssupporting

confidence: 71%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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On the Transition From Initial Leader to Stepped Leader in Negative Cloud‐to‐Ground Lightning

2020

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“…Figures 10c and 10d show diagrammatically that the second IB pulse occurs when the new UPF network ("3") connects to the pair of UPF networks that connected and made the first IB pulse. Bandara et al (2019) investigated negative NBEs (NNBEs) that initiated negative CG (−CG) flashes. NBE polarity is based on the polarity of the initial peak of the FA NBE waveform using the physics convention Figure 11.…”

Section: 1029/2020jd033191mentioning

confidence: 99%

The Mechanism of the Origin and Development of Lightning From Initiating Event to Initial Breakdown Pulses (v.2)

2020

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Based on experimental results of recent years, this article presents a qualitative description of a possible mechanism (termed the Mechanism) covering the main stages of lightning initiation, starting before and including the initiating event, followed by the initial electric field change (IEC), followed by the first few initial breakdown pulses (IBPs). The Mechanism assumes initiation occurs in a region of~1 km 3 with average electric field E > 0.3 MV/(m•atm), which contains, because of turbulence, numerous small "E th volumes" of~10 −4-10 −3 m 3 with E ≥ 3 MV/(m•atm). The Mechanism allows for lightning initiation by either of two observed types of events: a high-power, very high frequency (VHF) event such as a Narrow Bipolar Event or a weak VHF event. According to the Mechanism, both types of initiating events are caused by a group of relativistic runaway electron avalanche particles (where the initial electrons are secondary particles of an extensive air shower) passing through many E th volumes, thereby causing the nearly simultaneous launching of many positive streamer flashes. Due to ionization-heating instability, unusual plasma formations (UPFs) appear along the streamers' trajectories. These UPFs combine into three-dimensional (3-D) networks of hot plasma channels during the IEC, resulting in its observed weak current flow. The subsequent development and combination of two (or more) of these 3-D networks of hot plasma channels then causes the first IBP. Each subsequent IBP is caused when another 3-D network of hot plasma channels combines with the chain of networks caused by earlier IBPs.

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The Mechanism of the Origin and Development of Lightning from Initiating Event to Initial Breakdown Pulses (v.2)

Alexander

Marshall

Stolzenburg

2020

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To date, a non-controversial mechanism for the initiation and development of lightning in thunderstorm clouds has not been formulated as a sequential chain of events that begins with the first electron avalanches and ends with the appearance of a negative step leader. Based on experimental results of recent years, this article presents a qualitative description of a possible mechanism (termed the Mechanism) covering the main stages of lightning initiation, starting before and including the initiating event, followed by the initial electric field change (IEC), followed by the first few initial breakdown pulses (IBPs). The later transition from IBPs to a negative stepped leader is briefly described. The Mechanism assumes initiation occurs in a region of a thundercloud of ~1 km 3 with electric field E > 0.3 MV/(m•atm), which contains, because of turbulence, numerous small "E th -volumes" of ~0.001 m 3 with E ≥ 3 MV/(m•atm). The Mechanism allows for lightning initiation by two observed types of initiating events: a high power VHF event called an NBE (narrow bipolar event), or a weak VHF event. According to the Mechanism, both types of initiating events are caused by a group of relativistic runaway electron avalanche particles passing through many of the E th -volumes, thereby causing the nearly simultaneous launching of many positive streamer flashes. Due to ionization-heating instability, unusual plasma formations (UPFs) appear along the trajectories of the streamers. These UPFs combine into three-dimensional (3D) networks of hot plasma channels during the IEC, resulting in its observed weak current flow. The subsequent development and combination of two (or more) of these 3D networks of hot plasma channels then causes the first IBP. Each subsequent IBP is caused when another 3D network of hot plasma channels combines with the chain of networks caused by earlier IBPs.

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Characterizing three types of negative narrow bipolar events in thunderstorms

Cited by 21 publications

References 22 publications

On the Transition From Initial Leader to Stepped Leader in Negative Cloud‐to‐Ground Lightning

On the Transition From Initial Leader to Stepped Leader in Negative Cloud‐to‐Ground Lightning

The Mechanism of the Origin and Development of Lightning From Initiating Event to Initial Breakdown Pulses (v.2)

The Mechanism of the Origin and Development of Lightning from Initiating Event to Initial Breakdown Pulses (v.2)

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