High-speed video observations of natural cloud-to-ground lightning leaders – A statistical analysis

Campos, Leandro Z. S.; Saba, Marcelo M. F.; Warner, Tom A.; Pinto, O.; Krider, E. Philip; Orville, Richard E.

doi:10.1016/j.atmosres.2012.12.011

Cited by 88 publications

(98 citation statements)

References 72 publications

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“…[36] Other high-speed observations obtained of 10 +CG flashes on 9 September 2011 in northern Catalonia (not shown here) exhibited a recoil-active stage with invisible positive leaders below the cloud base, followed by downward acceleration of one positive leader, brightening strongly while reaching the highest speeds close to the ground, similar to the findings of Campos et al [2013]. This shows that a positive leader can return to bright, recoil-free propagation after a recoiling stage, at speeds similar to negative leaders.…”

Section: Der Velde and Montanyà: Asymmetries Of Leaders In Lightningsupporting

confidence: 69%

Asymmetries in bidirectional leader development of lightning flashes

Velde

Montanyà

2013

JGR Atmospheres

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Lightning flashes develop as a bidirectional tree, with a negative and a positive end propagating simultaneously into cloud charges of the opposite polarity. In recent years, this process has been modeled assuming that the bidirectional channel remains a zero‐net‐charge perfect conductor starting at the electric potential of its initial location. So far, both leader ends were treated identically. We summarize characteristics of bidirectional leader development of various lightning flashes registered by the Ebro 3‐D Lightning Mapping Array at the east coast of Spain, supplemented by high‐speed camera records. In order to follow the horizontal development of positive and negative leaders over time, a time‐distance‐altitude graph was designed, using the flash origin or a cloud‐to‐ground stroke as reference. The examples confirm that negative and positive leaders propagate at characteristic horizontal speeds (105 and 2 · 104 m s−1). The positive leader's low apparent speed corresponds to the phase when recoil processes are active. Very fast negative leaders (up to 8 · 105 m s−1) are detected in association with positive cloud‐to‐ground strokes. Negative leaders respawn repeatedly from the origin or as a retrograde negative leader at the positive branch. Positive leaders remain propagating throughout the flash or until reaching ground. We show that the velocity difference shifts the potential of the leader, increasing the gradient with cloud charge at the positive end while reducing it at the negative end. The positive section lowers its potential through retrograde negative leaders, eventually making it possible to emit a new negative leader into the upper positive potential well.

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Section: Der Velde and Montanyà: Asymmetries Of Leaders In Lightningsupporting

confidence: 69%

Asymmetries in bidirectional leader development of lightning flashes

Velde

Montanyà

2013

JGR Atmospheres

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“…A statistically significant study on the speed of stepped leaders was conducted recently by Campos et al [26]. They found average speeds of 3.4 × 10 5 m/s and 1.87 × 10 5 m/s at two sites, one in Southern Brazil and the other in Arizona.…”

Section: Resultsmentioning

confidence: 99%

“…Only 9% showed a decrease in speed with increasing leader length. Campos et al [26] also analyzed how the leader speed is related to the return increasing peak current. Even though there is some scatter in the data, there was a clear indication that the leader speeds increase with increasing peak current.…”

Section: Resultsmentioning

confidence: 99%

“…This complex behavior is actually observed in 46% of the stepped leaders. If we consider the average stepped leader speed observed over the last 2000 m or so in the study conducted by Campos et al [26], the observed value is about 3 × 10 5 m/s. This shows that, within the confines of the present leader model, the best parameters that approximate the experimental data are 1.0 × 10 6 m/s for the negative streamer speed and 2.0 × 10 6 V/m for the negative streamer potential gradient.…”

Section: Discussionmentioning

confidence: 99%

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Modeling the Stepping Process of Negative Lightning Stepped Leaders

Cooray

Arévalo

2017

Atmosphere

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A physical model based on the mechanism observed in experimental investigations is introduced to describe the formation of negative leader steps. Starting with a small length of a space leader located at the periphery of the negative streamer system of the stepped leader, the model simulates the growth and the subsequent formation of the leader step. Based on the model, the step length, the step forming time, and the propagation speed of stepped leaders as a function of the prospective return stroke peak current are estimated. The results show that the step length and the leader speed increase with increasing prospective return stroke current. The results also show that the speed of the stepped leader increases as it approaches the ground. For prospective return stroke currents in the range of 15 kA-60 kA, the step lengths lie within the range 5 m-100 m, the step forming times lie within the range 10 µs-250 µs, and the leader speed lies within the range 10 5 m/s −1.5 × 10 6 m/s. The results obtained are in reasonable agreement with the experimental observations.

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“…In an independent study, 62 negative stepped leaders, 76 negative dart leaders and 29 positive leaders were recorded and analyzed using highspeed cameras operating at frame rates ranging from 1,000 or 11,800 frames per second. The speed of positive leaders showed a clear tendency to increase whilst that of negative dart leaders to slow down when they approach ground [24].…”

Section: Lightning Characteristicsmentioning

confidence: 99%

Lightning Interactions with Humans and Lifelines

Kalair

Abas²,

Khan³

2013

JLR

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Lightning is one of the fascinating phenomena exhibiting tremendous natural power. It is source of awe, curiosity, enticement, inspiration as well as fear. On average, 50 lightning strikes occur on earth in one second. Fortunately not all of them kill people, albeit 10% people fall prey to lightning annually, out of which hardly 20 to 25% die. Lightning injures victims by heat, shockwave, intense brightness, radio waves, and secondary slip or fall mechanisms. Lightning injury is different from the normal electric shock as it involves transient flashover unlike the electrical contact freeze, wherein alternating (AC) and direct currents (DC) pass through the conductive interior body. Vacuity in knowledge is the driving force behind discoveries and inventions. Lightning experts had hardly developed any concurrence on lightning physics, and the observation of dark lightning complicated the Gordian knot. Lightning preventive, alerting and control devices help reduce fatality rates by the bolts out of blue skies. Lightning was considered to be the second cause of death making natural disasters after flashfloods but preventive measures have slithered it down to the third place in developed countries. Lightning prevention rule recommends 'when the thunder roars, go indoors'. This work describes lightning characteristics, damage thresholds to humans, machines, energy infrastructures, airplanes, wind turbines, light railway tractions, underground cables and pipelines. Power and energy lifelines such as transmission lines, oil tankers and gas or petroleum pipelines are susceptible to lightning strikes. Artificial rocket and laser triggered lightning protection and control techniques help to divert the lightning attacks. Interaction of lightning with power and energy infrastructures disrupts these lifelines. However, lightning itself is viewed as an extraterrestrial energy source. Lightning energy harvesting is an interesting application which has been investigated quantitatively.

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High-speed video observations of natural cloud-to-ground lightning leaders – A statistical analysis

Cited by 88 publications

References 72 publications

Asymmetries in bidirectional leader development of lightning flashes

Asymmetries in bidirectional leader development of lightning flashes

Modeling the Stepping Process of Negative Lightning Stepped Leaders

Lightning Interactions with Humans and Lifelines

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