Propagation of lightning generated transient electromagnetic fields over finitely conducting ground

The lightning-induced-damages in the mid-latitude regions are usually caused during severe thunderstorms. But the discharge parameters of natural lightning are difficult to be measured. Five lightning flashes have been artificially triggered with the rocket-wire technique during the passage of two severe thunderstorms. The discharge current and close electric field of return stroke in artificially triggered lightning have been obtained in microsecond time resolution by using current measuring systems and electric field change sensors. The results show that the five triggered lightning flashes include 1 to 10 return strokes, and the average return stroke current is 11.9 kA with a maximum of 21.0 kA and a minimum of 6.6 kA, similar to the subsequent return strokes in natural lightning. The half peak width of the current waveform is 39 µs, which is much larger than the usual result. The peak current of stroke I p (kA) and the neutralized charge Q(C) has a relationship of I p = 18.5Q 0.65 . The radiation field of return stroke is 5.9 kV·m −1 and 0.39 kV·m −1 at 60 m and 550 m, respectively. The radiation field decreases as r −1.119 with increase of horizontal distance r from the discharge channel. Based on the well-accepted transmission line model, the speed of return stroke is estimated to be about 1.4×10 8 m·s −1 , with a variation range of (1.1-1.6)×10 8 m·s −1 . Because of the similarities of the triggered lightning and natural lightning, the results in this article can be used in the protection design of natural lightning.artificially triggered lightning, characteristic discharge parameters, current waveform, electric field change in close distance, severe thunderstormThe serious lightning-induced damages are usually caused by the severe thunderstorm because of the very frequent lightning activities in the mid-latitude region. However, the discharge current and close electric and magnetic fields for natural lightning flashes are very difficult to be measured because of the low probability of striking at a certain object, and the understanding of lightning physical mechanism has been lagged, consequently. As a matter of fact, the lightning discharge can be triggered artificially by means of rocket-wire-trailing technique. The first triggered lightning over terrene was accomplished in France in 1973 [1] . A common technique for artificially triggering lightning involves launching a small rocket trailing a thin, grounded copper wire toward the charged cloud overhead. This technique for triggered lightning is called "classical" triggering. The lightning will be triggered successfully when the rocket reaches a height of several hundreds of meters in a favorable condition of thunderstorm electricity. Most frequently, triggered lightning flashes are negative, that is, they occur when the background electric field is oriented

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“…This is because the real ground has a limited conductivity. According to Cooray et al [26] , the ground conductivity is 10 −2 -10 −3 S·m −1 .…”

Section: The Signatures Of Electric Field Change At Different Distancesmentioning

confidence: 98%

Artificially triggered lightning and its characteristic discharge parameters in two severe thunderstorms

et al. 2007

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“…It is known that electromagnetic fields propagating over lossy ground suffer attenuation and distortion [e.g., Uman et al, 1976;Cooray et al, 2000]. A number of approximate expressions in both frequency and time domains have been used [e.g., Cooray and Lundquist, 1983;Cooray, 1992Cooray, , 2002Rubinstein, 1996;Shoory et al, 2005;Barbosa and Paulino, 2007] to account for the field propagation effects.…”

Section: Introductionmentioning

confidence: 99%

FDTD simulation of LEMP propagation over lossy ground: Influence of distance, ground conductivity, and source parameters

2015

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We have computed lightning electromagnetic pulses (LEMPs), including the azimuthal magnetic field H φ , vertical electric field E z , and horizontal (radial) electric field E h that propagated over 5 to 200 km of flat lossy ground, using the finite difference time domain (FDTD) method in the 2-D cylindrical coordinate system. This is the first systematic full-wave study of LEMP propagation effects based on a realistic return-stroke model and including the complete return-stroke frequency range. Influences of the return-stroke wavefront speed (ranging from c/2 to c, where c is the speed of light), current risetime (ranging from 0.5 to 5 μs), and ground conductivity (ranging from 0.1 mS/m to ∞) on H φ , E z , and E h have been investigated. Also, the FDTD-computed waveforms of E h have been compared with the corresponding ones computed using the Cooray-Rubinstein formula. Peaks of H φ , E z , and E h are nearly proportional to the return-stroke wavefront speed. The peak of E h decreases with increasing current risetime, while those of H φ and E z are only slightly influenced by it. The peaks of H φ and E z are essentially independent of the ground conductivity at a distance of 5 km. Beyond this distance, they appreciably decrease relative to the perfectly conducting ground case, and the decrease is stronger for lower ground conductivity values. The peak of E h increases with decreasing ground conductivity. The computed E h /E z is consistent with measurements of Thomson et al. (1988). The observed decrease of E z peak and increase of E z risetime due to propagation over 200 km of Florida soil are reasonably well reproduced by the FDTD simulation with ground conductivity of 1 mS/m.

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“…This is attributed to the fact that in the LF range the amplitude of even the largest IC pulses is significantly lower compared to that of the CG return strokes (Weidman et al, 1981). The amplitude difference between CG strokes and IC pulses increases even further with increasing propagation distance between the source and the lightning sensor (Cooray et al, 2000). Hence, more sensors will detect the radiation from a single CG discharge compared to an IC pulse.…”

Section: Resultsmentioning

confidence: 99%

Analysis of lightning outliers in the EUCLID network

et al. 2017

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Abstract. Lightning data as observed by the European Cooperation for Lightning Detection (EUCLID) network are used in combination with radar data to retrieve the temporal and spatial behavior of lightning outliers, i.e., discharges located in a wrong place, over a 5-year period from 2011 to 2016. Cloud-to-ground (CG) stroke and intracloud (IC) pulse data are superimposed on corresponding 5 min radar precipitation fields in two topographically different areas, Belgium and Austria, in order to extract lightning outliers based on the distance between each lightning event and the nearest precipitation. It is shown that the percentage of outliers is sensitive to changes in the network and to the location algorithm itself. The total percentage of outliers for both regions varies over the years between 0.8 and 1.7 % for a distance to the nearest precipitation of 2 km, with an average of approximately 1.2 % in Belgium and Austria. Outside the European summer thunderstorm season, the percentage of outliers tends to increase somewhat. The majority of all the outliers are low peak current events with absolute values falling between 0 and 10 kA. More specifically, positive cloud-toground strokes are more likely to be classified as outliers compared to all other types of discharges. Furthermore, it turns out that the number of sensors participating in locating a lightning discharge is different for outliers versus correctly located events, with outliers having the lowest amount of sensors participating. In addition, it is shown that in most cases the semi-major axis (SMA) assigned to a lightning discharge as a confidence indicator in the location accuracy (LA) is smaller for correctly located events compared to the semimajor axis of outliers.

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Propagation of lightning generated transient electromagnetic fields over finitely conducting ground

Cited by 61 publications

References 15 publications

Artificially triggered lightning and its characteristic discharge parameters in two severe thunderstorms

Artificially triggered lightning and its characteristic discharge parameters in two severe thunderstorms

FDTD simulation of LEMP propagation over lossy ground: Influence of distance, ground conductivity, and source parameters

Analysis of lightning outliers in the EUCLID network

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