Elve doublets and compact intracloud discharges

Marshall, R. A.; Silva, Caitano L. da; Pasko, Victor P.

doi:10.1002/2015gl064862

Cited by 34 publications

(45 citation statements)

References 30 publications

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“…They also have much larger magnitude, because the electric field radiated by a vertical current is proportional to

\sin θ

( θ is the angle between

\overset{R}{true}

and the vertical direction), which rapidly increases with increasing θ when θ is small. The reflected wave can be thought as produced by an image current source located below the ground (Marshall et al, ; Uman et al, ). The angle θ for the reflected wave at 0.4 ms shown in Figure c is much smaller than that for the direct wave, so the magnitude of the reflected wave is smaller.…”

Section: Simulation Resultsmentioning

confidence: 99%

“…When viewed from a spacecraft at 700 km altitude right above the center, the elve has a perfectly circular shape, similar to the view from right below the center (Inan et al, ; Marshall, ; Veronis et al, ). Initially, for example, at 2.54 ms, there are two concentric rings corresponding to the wavefronts of the direct and ground‐reflected waves, which indicates that elves associated with TGFs are also “doublets” as those produced by CIDs (Marshall et al, ). Note that the substructure in the direct or reflected wave is completely lost in the emission intensity distribution, not only because the lifetime of the N 2 (B) states is comparable to the time separation between the two extrema of the current moment derivative, as mentioned earlier, but also because the integration to calculate the emission intensity is taken along a slanted path through an emission region with a vertical thickness of about 20 km.…”

Section: Simulation Resultsmentioning

confidence: 99%

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Elves Accompanying Terrestrial Gamma Ray Flashes

2017

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This paper reports a modeling study of the optical phenomenon in the lower ionosphere known as elves that may accompany terrestrial gamma ray flashes (TGFs). Recent research has indicated that the in‐cloud (IC) discharge processes, termed energetic in‐cloud pulses (EIPs), associated with some TGFs can produce a current moment waveform with a peak of hundreds of kA km and a duration of 10 μs. Simulations using the source current moment waveform associated with a Fermi TGF indicate that the radiated electric field at ionospheric altitudes reaches a few times the threshold electric field to excite the optical emissions. A bright elve is therefore induced, with the intensity reaching tens of Megarayleigh, comparable to the brightest elves caused by cloud‐to‐ground lightning. Because of the strong electromagnetic field radiated, significant blue emissions from the second positive band system of N2 and the first negative band system of N 2+ are excited, besides the dominant red emissions from the first positive band system of N2. The elves caused by EIPs with durations of ∼10 μs are elve doublets. For EIPs of longer durations, for example, 30–40 μs, elve multiplets greater than two can be produced. We conclude that elves can be produced by an IC lightning process previously unconnected to elves and that at least some TGFs should have accompanying optical signatures in the lower ionosphere. In addition, TGFs of short durations are more likely to have accompanying elves, because their source currents vary more rapidly.

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“…They also have much larger magnitude, because the electric field radiated by a vertical current is proportional to

\sin θ

( θ is the angle between

\overset{R}{true}

Section: Simulation Resultsmentioning

confidence: 99%

Section: Simulation Resultsmentioning

confidence: 99%

Elves Accompanying Terrestrial Gamma Ray Flashes

2017

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“…For a wavefront propagating as z f = h 1 + v t , it is straightforward to see that its amplitude decreases exponentially with distance as

e^{- (z_{f} - h_{1}) / vτ}

. Hence, the 1/ e length scale is equivalent to 2 v L / R , and it is inversely proportional to the channel's linear resistance. Modified transmission line Gaussian (MTLG) (this work and Marshall et al []). This model is characterized by a Gaussian spatial distribution centered at some point h p along the channel.…”

Section: Formulation Of Transmission Line Modelsmentioning

confidence: 99%

“…The 1/ e scales below and above the peak of the current distribution are

h_{r} = αℓ / \sqrt{3 \ln (10)}

and

h_{f} = (1 - α) ℓ / \sqrt{3 \ln (10)}

, respectively. The MTLG model was introduced by Marshall et al [] to better represent the vertical current distribution obtained from physics‐based modeling of CIDs and other leader‐related in‐cloud discharge processes [ da Silva and Pasko , ; da Silva , ]. Specifically, the fact that the current is (approximately) zero at both channel extremities and peaks somewhere in the middle of it ensures charge neutrality at the source at all times [ da Silva and Pasko , ; Marshall et al , ].…”

Section: Formulation Of Transmission Line Modelsmentioning

confidence: 99%

Mathematical constraints on the use of transmission line models to investigate the preliminary breakdown stage of lightning flashes

2016

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The initial stage of in-cloud lightning development is characterized by a series of initial breakdown pulses (IBPs), observed as abrupt electric field changes at a remote sensor. Recent studies have attributed this process to the stepwise elongation of a negative lightning leader channel and used transmission line (TL) models to interpret the observed electromagnetic emission. In these models a current pulse is injected at the base of the channel, propagates along it, and the current parameters are adjusted to fit the measured IBPs. In this paper we explore the limitations of TL models by comparing four of its variants: the classic TL (with no attenuation) and three modified transmission line models that have different current attenuation characteristics, i.e., following linear, exponential, and Gaussian functions. For a compact channel (less than a few hundred meters long) all four models tend to produce similar electromagnetic signatures, and nearly identical waveforms can be obtained by simply varying the channel length. It is impossible to simultaneously identify, with confidence, both channel length and the speed of current wave propagation at the source by matching a far-field waveform. The field-to-current conversion factor for in-cloud sources is not a constant and can vary by as much as 2 orders of magnitude depending on channel length and current pulse risetime. This conclusion contrasts with the assumption used by the National Lightning Detection Network, that the field-to-current conversion can be performed by a multiplicative constant, as it is done for return strokes in cloud-to-ground lightning.

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“…Recent advances in lightning detection have raised interest in probing the ionospheric D/E region with lightning sferics (radio atmospherics). The lightning sferic has been used to investigate the EDP of the lower ionosphere with various models: the modified LWPC (Cheng et al, ; Cheng & Cummer, ; Cummer, ; Cummer et al, ; Cummer & Inan, ; McCormick et al, ), the FDTD model (Han et al, ; Han & Cummer, , ; Marshall, ; Marshall et al, ), the multilayer media full‐wave model (Lay et al, ; Lehtinen & Inan, ; Shao et al, ), and the RT model (Qin et al, ).…”

Section: Introductionmentioning

confidence: 99%

A Comparative Study of the Ray Theory Model With the Finite Difference Time Domain Model for Lightning Sferic Transmission in Earth‐Ionosphere Waveguide

et al. 2019

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The lightning sferic has been shown to be a valuable radio signal for detecting perturbations of the lower ionosphere caused by the lightning activity itself and by other terrestrial and space events (Shao et al., 2012, https://doi.org/10.1038/ngeo1668). Adding to many existing methods, we have recently proposed an improved ray theory (RT) model for investigating the lightning sferic transmission in the Earth‐ionosphere waveguide (Qin et al., 2017, https://doi.org/10.1002/2016JD025599). In the present study, a further modification to the RT model was made to increase its accuracy in modeling the lightning sferic in a broader frequency band and a larger distance range. The modification included two aspects: a new incident angle finding technique and a novel method for deriving the high‐order hop series. To quantitatively evaluate the effectiveness of the modification, a comparative study of this modified RT model with its previous version and the full‐wave finite difference time domain model was carried out. The results showed that this modified RT model did better than its previous version and was in close agreement with the full‐wave finite difference time domain method in modeling the lightning sferic in frequencies bands lower to 3, 5, and 7 kHz for distances up to 500, 800, and 1,000 km, respectively.

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Elve doublets and compact intracloud discharges

Cited by 34 publications

References 30 publications

Elves Accompanying Terrestrial Gamma Ray Flashes

Elves Accompanying Terrestrial Gamma Ray Flashes

Mathematical constraints on the use of transmission line models to investigate the preliminary breakdown stage of lightning flashes

A Comparative Study of the Ray Theory Model With the Finite Difference Time Domain Model for Lightning Sferic Transmission in Earth‐Ionosphere Waveguide

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