Positive leader characteristics from high‐speed video observations

Saba, Marcelo M. F.; Cummins, K. L.; Warner, Tom A.; Krider, E. Philip; Campos, Leandro Z. S.; Ballarotti, M. G.; Pinto, O.; Fleenor, Stacy A.

doi:10.1029/2007gl033000

Cited by 97 publications

(137 citation statements)

References 15 publications

Supporting

Mentioning

125

Contrasting

Order By: Relevance

“…One observational feature that supports the aforementioned mechanism is that GJs emerge from thundercloud tops with speeds on the order of or less than the lower limit of streamer speeds, which is 10 5 m/s [Bazelyan and Raizer, 2000, p. 39] but consistent with speeds of laboratory and lightning leaders [Bazelyan and Raizer, 1998, Section 6.2]. For instance, Briels et al [2008] have measured laboratory streamer speeds in the range 1-40 10 5 m/s, while Andreev et al [2008] and Saba et al [2008] have measured speeds in the range 1-5 10 4 m/s and 3-60 10 4 m/s, for laboratory and lightning leaders, respectively. Modeling results of leader speeds at reduced air densities reiterate this assertion Pasko, 2012, 2013].…”

Section: Gigantic Jet Acceleration As Evidence Of Its Vertical Structmentioning

confidence: 99%

Dynamics of streamer‐to‐leader transition at reduced air densities and its implications for propagation of lightning leaders and gigantic jets

2013

View full text Add to dashboard Cite

[1] In this paper we present modeling studies of air heating by electrical discharges in a wide range of pressures. The developed model is capable of quantifying the different contributions for heating of air at the particle level and rigorously accounts for the vibration-dissociation-vibration coupling. The model is validated by calculating the breakdown times of short air gaps and comparing to available experimental data. Detailed discussion on the role of electron detachment in the development of the thermal-ionizational instability that triggers the spark development in short air gaps is presented. The dynamics of fast heating by quenching of excited electronic states is discussed and the scaling of its main channels with ambient air density is quantified. The developed model is employed to study the streamer-to-leader transition process and to obtain its scaling with ambient air density. Streamer-to-leader transition is the name given to a sequence of events occurring in a thin plasma channel through which a relatively strong current is forced through, culminating in heating of ambient gas and increase of the electrical conductivity of the channel. This process occurs during the inception of leaders (from sharp metallic structures, from hydrometeors inside the thundercloud, or in virgin air) and during their propagation (at the leader head or during the growth of a space leader). The development of a thermal-ionizational instability that culminates in the leader formation and propagation is characterized by a change in air ionization mechanism from electron impact to associative ionization and by contraction of the plasma channel. The introduced methodology for estimation of leader speeds shows that the propagation of a leader is limited by the air heating of every newly formed leader section. It is demonstrated that the streamer-to-leader transition time has an inverse-squared dependence on the ambient air density at near-ground pressures, in agreement with similarity laws for Joule heating in a streamer channel. Model results indicate that a deviation from this similarity scaling occurs at very low air densities, where the rate of electronic power deposition is balanced by the channel expansion, and air heating from quenching of excited electronic states is very inefficient. These findings place a limit on the maximum altitude at which a hot and highly conducting lightning leader channel can be formed in the Earth's atmosphere, result which is important for understating of the gigantic jet (GJ) discharges between thundercloud tops and the lower ionosphere. Simulations of leader speeds at GJ altitudes demonstrate that initial speeds of GJs are consistent with the leader propagation mechanism. The simulation of a GJ, escaping upward from a thundercloud top, shows that the lengthening of the leader streamer zone, in a medium of exponentially decreasing air density, determines the existence of an altitude at which the streamer zones of GJs become so long that they dynamically extend (jump) all the way to th...

show abstract

Section: Gigantic Jet Acceleration As Evidence Of Its Vertical Structmentioning

confidence: 99%

Dynamics of streamer‐to‐leader transition at reduced air densities and its implications for propagation of lightning leaders and gigantic jets

2013

View full text Add to dashboard Cite

show abstract

“…The first type corresponds to the ordinary +CG [27] Of all the positive CGs in our data set, 118 (63.78%) of the positive CG flashes were ordinary positive CG flash, 39 (21.08%) exhibited IC discharge only after the strokes, 10 (5.41%) exhibited IC discharge only before the strokes, and 18 (9.73%) had IC discharge both before and after the strokes (see Table 5). If the IC discharge was recorded during the 200 ms pre-trigger time and no obvious preliminary breakdown and leader processes can be identified, we attribute this kind of positive CG flashes to be initiated by intracloud discharges, as found by Kong et al [2008] and Saba et al [2008] using high-speed video observations. The preliminary breakdown and leader processes are not considered as intracloud discharge in our analysis.…”

Section: Morphologies Of Positive Cg Flashes Accompanied By Ic Dischargementioning

confidence: 99%

Characteristics of positive cloud‐to‐ground lightning in Da Hinggan Ling forest region at relatively high latitude, northeastern China

Qie

Wang

et al. 2013

JGR Atmospheres

View full text Add to dashboard Cite

[1] In 2009 and 2010, a multistation network of fast and slow antennas was installed on the edge of a relatively high latitude forest region in Da Hinggan Ling (50.4°N, 124.1°E) of northeastern China. The documented 185 positive cloud-to-ground (CG) flashes containing 196 return strokes were analyzed in the paper. It was found that 71.89% of the positive CG flashes contained continuing current. The average duration of continuing current was short with an arithmetic mean value of 33.29 ms and a geometric mean value of 16.74 ms; only one continuing current lasted longer than 150 ms, probably because of the small size of the storm cell in this relatively high latitude region. The vast majority (94.59%) of positive CG flashes was characterized by a single stroke, and the average number of stroke per flash is 1.06. The average charge transferred by positive stroke and continuing current, based upon the analysis of five flashes with well-documented simultaneous measurements of more than five stations, was +5.2 C from a height of 6.0 km (above ground) and +10.2 C from a height of 6.4 km, respectively. The charge moment for +CG strokes ranged from +13.7 C km to +55.9 C km, while that for continuing current ranged from +29.0 C km to +96.9 C km, respectively. The preliminary breakdown process in positive CG flashes can be classified into three types, namely type S (same), type D (different), and type C (chaotic) according to the disparities in the initial polarity of bipolar pulses from the return stroke, which account for 62.92%, 23.60%, and 13.48%, respectively. According to the electric field waveforms indicative (or not indicative) of intracloud (IC) discharge, positive CG flashes are classified into four types, i.e., ordinary positive CG flash (63.78%), hybrid +CG-IC flash (21.08%), hybrid IC-+CG flash (5.41%), and hybrid IC-+CG-IC flash (9.73%). About 15.14% of the recorded positive CG flashes were byproduct of IC lightning discharge.

show abstract

“…However, there are also reports of much faster positive leaders. For example, Saba et al [2008] observed speeds of downward positive leaders in the range of 0.3 to 6 · 10 5 m s À1 with a mean of 2.7 · 10 5 m s À1 . Biagi et al [2011] recorded a similar speed in an upward leader, up to 2.1 · 10 5 m s À1 .…”

Section: Introductionmentioning

confidence: 99%

“…Observed with high-speed cameras, they look like luminous streaks occurring 3000-5000 times per second [Montanyà et al, 2012], revealing the locations of barely visible positive leader branches [Saba et al, 2008]. Their speed (>4 · 10 6 m s À1 ) [e.g., Saba et al, 2008] is rarely resolved by present VHF time-of-arrival systems, but they are detectable and often used to identify negative charge layers [Rust et al, 2005].…”

Section: Introductionmentioning

confidence: 99%

Asymmetries in bidirectional leader development of lightning flashes

Velde

Montanyà

2013

JGR Atmospheres

View full text Add to dashboard Cite

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.

show abstract

Positive leader characteristics from high‐speed video observations

Cited by 97 publications

References 15 publications

Dynamics of streamer‐to‐leader transition at reduced air densities and its implications for propagation of lightning leaders and gigantic jets

Dynamics of streamer‐to‐leader transition at reduced air densities and its implications for propagation of lightning leaders and gigantic jets

Characteristics of positive cloud‐to‐ground lightning in Da Hinggan Ling forest region at relatively high latitude, northeastern China

Asymmetries in bidirectional leader development of lightning flashes

Contact Info

Product

Resources

About