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Lightning can be defined as a transient, high-current (typically tens of kA) electric discharge in air whose length is measured in km. As for any discharge in air, lightning channel is composed of ionized gas, that is, of plasma, whose peak temperature is typically 30,000 K, about five times higher than the temperature of the surface of the Sun. Lightning was present on Earth long before human life evolved and it may even have played a crucial role in the evolution of life on our planet. The global lightning flash rate is some tens to a hundred km per second. Each year, some 25 million cloud-to-ground lightning discharges occur in the United States, and this number is expected to increase by about 50% due to global warming over the 21st century. Lightning initiates many forest fires, and over 30% of all electric power line failures are lightning related. Each commercial aircraft is struck by lightning on average once a year. A lightning strike to an unprotected object or system can be catastrophic. In the first part of the article, an overview of thunderclouds and their charge structure is given, basic lightning terminology is introduced, and different types of lightning (including the so-called rocket-triggered lightning) are described. For the most common negative cloud-to-ground lightning, main lightning processes are identified and the existing hypotheses of lightning initiation in thunderclouds are reviewed.

Recent upgrades of the low-cost lightning detection and waveform storage system (LDWSS) are presented. The system has been developed for research and operational use in the Amazon region of Brazil and it has been in operation in this region since November 1, 2017. The original version of the LDWSS operated for 10 months at the Lightning Observatory in Gainesville, Florida, where it was calibrated and tested. Two main modifications implemented include the improvement of the effective dynamic range and the capability to detect lightning in different frequency bands. The improvements were achieved by using two pre-amplifiers working in parallel, a new processing (smart saving) algorithm, and programmable analog filters. As a result, a single, low-cost lightning electric field measuring system allows one to record both close and far lightning events with good amplitude resolution and without saturation, and study both wideband and narrow-band (for example, very low frequency) field signatures of lightning, without modifying the hardware.

In this chapter, basic lightning terminology is introduced, different types of lightning are described, and main lightning processes are identified. For the most common negative cloud -to -ground lightning, the number of strokes per flash, interstroke intervals, flash duration, multiple channel terminations on ground, and relative stroke intensity within the flash are discussed. Traditional lightning parameters needed in engineering applications include lightning peak current, maximum current derivative, average current rate of rise, current risetime, current duration, charge transfer, and specific energy (action integral), all derivable from direct current measurements.

Electromagnetic computation methods (ECMs) have been widely used in analyzing lightning electromagnetic pulses (LEMPs) and lightning-caused surges in various systems. One of the advantages of ECMs, in comparison with circuit simulation methods, is that they allow a self-consistent, full-wave solution for both the transient current distribution in a three-dimensional conductor system and resultant electromagnetic fields, although they are computationally expensive. Among ECMs, the finite-difference time-domain (FDTD) method has been the most frequently used in lightning electromagnetic field and surge simulations. In this chapter, applications of the FDTD method to lightning electromagnetic field and surge simulations are reviewed. The applications include (i) surges on grounding electrodes, (ii) lightning surges on overhead power transmission lines (TLs) and towers, (iii) lightning surges on overhead power distribution and telecommunication lines, (iv) lightning electromagnetic environment and surges in power substations, (v) lightning surges on underground power and telecommunication cables, (vi) lightning surges in wind-turbine-generator towers, (vii) lightning surges in photovoltaic (PV) arrays, (viii) lightning surges and electromagnetic environment in buildings, (ix) lightning electromagnetic fields at close and far distances, and others.

In this paper, we simulated transient voltages across insulators and back-flashover at the transmission line tower struck by lightning in the presence of corona on the ground wires. The FDTD method and simplified (engineering) model of corona discharge were used. Three two-circuit 60-m high towers, separated by 400 m, with two overhead ground wires, and six phase conductors (two three-phase circuits) were considered. Back-flashover was assumed to occur at the upper, middle, or lower phase. Operating voltages of phase conductors were modeled by using a voltage source inserted between each phase conductor and ground. It is observed that ground-wire corona serves to reduce voltage peaks and delay the occurrence of flashover. For the upper-phase back-flashover due to a positive 50-kA stroke, the peak voltages across the upper-, middle-, and lower-phase insulators are reduced by 11%, 12%, and 12% by the ground-wire corona, and for a negative 50-kA stroke they are reduced by 8%, 9%, and 9%. Influences of ground-wire corona on transient voltages were also studied for the back-flashover at the middle or lower phase. Presence of operating voltages can lead to either increase or decrease of the peak of transient voltage, with the change being less than 20%. To the best of our knowledge, this is the first FDTD simulation of back-flashover at a transmission-line tower considering both ground-wire corona and operating voltages.

Machine learning (ML) techniques have been used around the world to solve different problems. In this work, we applied ML techniques to estimate lightning distance for return strokes (RS) in negative cloud-to-ground (-CG) flashes. The approach uses E-field records from a single-station system. A lightning electric field waveform dataset containing more than 1500 waveforms of negative RS recorded at LOG, Florida, US was used to train and validate the ML classifiers. The dataset was split into day time and night time records. For day-time records, the quadratic Support Vector Machine (SVM) classifier was the one with the best accuracy (80%) and for night-time, the best one was the linear SVM with an accuracy of 88%. The ML classifiers were applied to estimate lightning distance in thunderstorms in the Amazon region of Brazil, and the results were compared against GOES-16 images and STARNET lightning location data. The main application of such methodology is for regions with no lightning location systems or no communication links to obtain lightning location data.

A bipolar cloud-to-ground lightning flash was observed to exhibit two types of polarity reversal associated with the first two strokes separated by a not-unduly-long time interval of 70 ms. The first stroke was negative and had a peak current of -101 kA. The second stroke was positive, had a peak current of 16 kA, and was followed by a 122-ms long bipolar continuing current. The first two strokes, including the bipolar continuing current, occurred in the same channel to ground, whose imaged 2D length was 4.2 km. The occurrence of positive stroke in the negative-stroke channel is highly unusual. The 2D speed versus height profiles for the negative stepped leader of the first stroke and, for the first time, for the positive leader in the previously conditioned, first-stroke channel were examined and the average speeds were found to be 4.7 × 105 m/s and 7.2 × 105 m/s, respectively.

We present a study focused on pulses superimposed on the initial continuous current of upward negative discharges. The study is based on experimental data consisting of correlated lightning current waveforms recorded at the instrumented Santis Tower in Switzerland and electric fields recorded at a distance of 14.7 km from the tower. Two different types of pulses superimposed on the initial continuous current were identified: (1) M-component-type pulses, for which the microsecond-scale electric field pulse occurs significantly earlier than the onset of the current pulse, and (2) fast pulses, for which the onset of the field matches that of the current pulse. We analyze the currents and fields associated with these fast pulses (return-stroke type (RS-type) initial continuous current (ICC) pulses) and compare their characteristics with those of return strokes. A total of nine flashes containing 44 RS-type ICC pulses and 24 return strokes were analyzed. The median current peaks associated with RS-type ICC pulses and return strokes are, respectively, 3.4 kA and 8 kA. The associated median E-field peaks normalized to 100 km are 1.5 V/m and 4.4 V/m, respectively. On the other hand, the electric field peaks versus current peaks for the two data sets (RS-type ICC pulses and return strokes) are characterized by very similar linear regression slopes, namely, 3.67 V/(mkA) for the ICC pulses and 3.77 V/(mkA) for the return strokes. Assuming the field-current relation based on the transmission line model, we estimated the apparent speed of both the RS-type ICC pulses and return strokes to be about 1.4 x 10(8) m/s. A strong linear correlation is observed between the E-field risetime and the current risetime for the ICC pulses, similar to the relation observed between the E-field risetime and current risetime for return strokes. The similarity of the RS-type ICC pulses with return strokes suggests that these pulses are associated with the mixed mode of charge transfer to ground.

In this paper, we have computed lightning-induced voltages on overhead distribution lines in the presence of nearby buildings using the 3-D finite-difference time-domain method. In the simulations, four-conductor lines with surge arresters and pole transformers are considered. It appears that the presence of nearby buildings causes reduction of lightning induced voltages, as expected. The observed trend is in general agreement with that reported from the small-scale experiment by Piantini et al.

We have computed lightning electromagnetic pulses (LEMPs), including the azimuthal magnetic field Hφ, vertical electric field Ez, and horizontal (radial) electric field Eh 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 Hφ, Ez, and Eh have been investigated. Also, the FDTD-computed waveforms of Eh have been compared with the corresponding ones computed using the Cooray-Rubinstein formula. Peaks of Hφ, Ez, and Eh are nearly proportional to the return-stroke wavefront speed. The peak of Eh decreases with increasing current risetime, while those of Hφ and Ez are only slightly influenced by it. The peaks of Hφ and Ez 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 Eh increases with decreasing ground conductivity. The computed Eh/Ez is consistent with measurements of Thomson et al. (1988). The observed decrease of Ez peak and increase of Ez 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.

The full scale test house was equipped with the lightning protection system and connected to the 15 kV/400 V transformer station. The simulated stroke current was injected into the installation with a current surge generator. Distribution of current in the lightning protection system and connected power supply installation is presented. Measurements were done for several configurations of the LPS, and for current amplitudes ranging from 1 to 10 kA. The results indicated variation with both the amplitude and the shape of the waveforms. The resistance was measured for several groundings individually and for entire grounding system with respect to the surge generator location. Measured waveforms showed frequency-dependent behavior of the circuit. Therefore, in order to improve current simulation accuracy the grounding system impedance should be considered rather than pure resistance. The vertical ground rods of the test house have capacitive impedances, while the long underground cable connected to the grounding system of the transformer has inductive impedance.

In this paper, a simplified model of corona discharge for the finite-difference time-domain (FDTD) computations has been applied to analysis of transient voltages at the tower of a transmission line caused by direct lightning strikes to an upper phase conductor. In the simulations, three 40-m towers, separated by 300 m, with one overhead ground wire and three phase conductors are employed. Corona is assumed to occur only on the upper phase conductor struck by lightning. The progression of corona streamers from the conductor is represented as the radial expansion of cylindrical conducting region around the conductor. The reduction of transient-voltage peak due to corona is not very significant, so that the voltage at the nearest tower exceeds the insulation level of 66/77 kV power line considered in this paper. For a 10-kA peak current, the upper-phase-conductor voltage peaks are reduced by 26% and 21% for a positive stroke with 1-μs- and 3-μs-risetime currents, respectively, and those for negative-stroke case are reduced by 18% and 13%, respectively. For a 20-kA peak current, the corresponding upper-phase-voltage peaks are reduced by 32% and 25% for the positive-stroke case, and those for the negative-stroke case are reduced by 22% and 15%.

In this paper, lightning-induced voltages on multiconductor lines with surge arresters and pole transformers have been computed using the 3-D finite-difference time-domain method. This method uses a subgrid model, in which spatial discretization is fine (cell side length is 0.5 m) in the vicinity of overhead wires and coarse (cell side length is 5 m) in the rest of the computational domain. In the simulations, four-conductor lines with surge arresters and pole transformers are considered. The 1-cm-radius overhead conductors are represented by placing a wire having an equivalent radius of about 0.12 m (≈ 0.23 × 0.5 m) in the center of an artificial rectangular prism having a cross-sectional area of 1 m × 1 m (2 cells × 2 cells) and the modified (relative to air) constitutive parameters: lower electric permittivity and higher magnetic permeability. The computed lightning-induced voltage waveforms agree reasonably well with the corresponding ones measured in the small-scale experiment of Piantini et al. (2007).

The waveforms of lightning return-stroke electromagnetic fields on ground are studied using the transmission line model. Approximate expressions to calculate lightning electromagnetic fields at near and far ranges are presented. It is found that the waveforms of lightning electric and magnetic fields in the time domain at both near and far ranges can be expressed approximately as the channel-base current waveform multiplied by a factor which is a function of the return-stroke speed v and the horizontal distance r between the return-stroke channel and the observation point on ground. The ranges at which the approximate expressions are valid are determined. The ranges of validity increase with increasing the return-stroke speed, and the near and far field approximate expressions converge to the exact formula as the return-stroke speed approaches the speed of light.

in this paper, we present a new tool for lightning-induced voltage calculations. The tool, a circuit model which can be integrated into power systems simulators, is based on the theory developed by Andreotti et al. (2001, 2009, 2013). In Part II, the accuracy, stability, and efficiency of the new tool are demonstrated via comparison with other solutions/codes found in the literature and with experimental data

in the companion paper (Part I), a new tool for lightning-induced voltage calculations, called CiLIV, has been presented. In this paper (Part II), predictions made with the new tool are compared to experimental data and to outputs of analytical procedures/numerical codes found in the literature.

We have evaluated the performance characteristics of the Earth Networks Total Lightning Network (ENTLN) using, as ground truth, data for 245 negative return strokes and 138 kiloampere-scale (≥1 kA) superimposed pulses in 57 flashes triggered from June 2009 to August 2012 at Camp Blanding, Florida. The performance characteristics were determined both for the ENTLN processor that had been in service at the time of acquiring triggered-lightning data (June 2009 to August 2012) and for the new ENTLN processor, introduced in November 2012. So, evaluation for the new processor simulates ENTLN output as if the new processor were in service from June 2009 to August 2012. For the same ground-truth data set and the same evaluation methodology, different performance characteristics for those two processors were obtained. For the old processor, flash detection efficiency was 77%, stroke detection efficiency was 49%, percentage of misclassified events was 61%, median location error was 631 m, and median absolute current estimation error was 51%. For the new processor, flash detection efficiency was 89%, stroke detection efficiency was 67%, percentage of misclassified events was 54%, median location error was 760 m, and median absolute current estimation error was 19%.

We examine the effect of channel branching on electric field waveforms produced by first return strokes in negative cloud-to-ground lightning using a modified transmission line model. From computed return stroke electric field waveforms it is found that the presence of an ungrounded branch results in sharper initial peak and a secondary peak in the falling part of the return stroke waveform. The time interval between the primary and secondary peaks depends upon the height of the branching point above ground and the speed at which the incident current wave moves upward from the ground. The presence of branch serves to slightly decrease the magnitude of the opposite polarity overshoot. The effects of the height of the branching point above ground, fraction of total channel current flowing to the branch, and current reflections from the branch unconnected end are illustrated.

The finite-difference time-domain (FDTD) method in the 2D cylindrical coordinate system was used to compute the nearly-full-frequency-bandwidth vertical electric field and azimuthal magnetic field waveforms produced on the ground surface by lightning return strokes. The lightning source was represented by the modified transmission-line model with linear current decay with height (MTLL model), which was implemented in the FDTD computations as an appropriate vertical phased-current-source array. The conductivity of atmosphere was assumed to increase exponentially with height, with different conductivity profiles being used for daytime and nighttime conditions. The fields were computed at distances ranging from 50 to 500 km. Skywaves (reflections from the ionosphere) were identified in computed waveforms and used for estimation of apparent ionospheric reflection heights. It was found that our model reproduces reasonably well the daytime electric field waveforms measured at different distances and simulated (using a more sophisticated propagation model) by Qin et al. [2017]. Sensitivity of model predictions to changes in the parameters of atmospheric conductivity profile, as well as influences of the lightning source characteristics (current waveshape parameters, return-stroke speed, and channel length) and ground conductivity were examined.

International audience; In this paper, we present and discuss simultaneous records of current and wideband electric field waveforms at 380 km distance from the strike point associated with an upward bipolar flash initiated from the Säntis Tower. The flash contains 23 negative strokes and one positive stroke. The height of the ionospheric reflection for the positive pulse was inferred to be about 94.9 km, a value which is significantly higher than for negative pulses of this same flash, which range from 73 to 81 km. It is also found that the ratio of the peak field to the current peak is about two times smaller for the positive pulse compared to negative pulses. This difference can be attributed to a lower return stroke speed for the positive stroke compared to that for negative strokes, and also to the fact that the enhancement of the electric field due to the presence of the tower and the mountain might be more significant for negative pulses, which are characterized by faster risetimes, than for the positive pulse. Keywords—Bipolar lightning flash, simultaneous current and field measurement, ionospheric reflection, field-to-current conversion factor

In this paper, a simplified model of corona discharge for the finite-difference time-domain (FDTD) computations has been applied to analysis of lightning-induced voltages at different points along a 5-mm radius, 1-km long single overhead wire taking into account corona space charge around the wire. Both perfectly conducting and lossy ground cases were considered. FDTD computations were performed using a 3-D nonuniform grid. The progression of corona streamers from the wire is represented as the radial expansion of cylindrical weakly conducting (40 μS/m) region around the wire. The magnitudes of FDTD-computed lightning-induced voltages in the presence of corona discharge are larger than those computed without considering corona. The observed trend is in agreement with that reported by Nucci et al. and by Dragan et al ., although the increase predicted by our full-wave model (up to 5% and 9% for negative and positive lightning return strokes, respectively) is less significant than in their studies (up to a factor of 2) based on the distributed-circuit model with sources specified using the electromagnetic field theory. The disparity is likely to be related to the use of different charge-voltage diagrams, explicitly assumed by Nucci et al. and Dragan et al . and resulting from our FDTD model with corona in the present study. When corona is considered, there is a tendency for induced-voltage rise time to increase. It appears that the distributed impedance discontinuity, associated with the corona development on the wire, is the primary reason for higher induced-voltage peaks and longer voltage rise times, compared to the case without corona.

In this paper, a simplified model of corona discharge for the finite-difference time-domain (FDTD) computations has been applied to the analysis of transient voltages across insulators of a transmission line struck by lightning. In the simulation, three 60-m towers, separated by 200 m, with one overhead ground wire and three-phase conductors are employed. The progression of corona streamers from the ground wire is represented as the radial expansion of cylindrical conducting region around the wire. On the basis of the computed results, the effect of corona discharge at the ground wire on transient insulator voltages is examined. The insulator voltages are reduced by corona discharge on the ground wire. The reduction of insulator-voltage peak due to the ground-wire corona is not very significant: the upper-, middle-, and lower-phase-voltage peaks are reduced by 15, 14, and 13% for a positive stroke with 50-kA-peak and 3-μs-risetime current, and those for the negative stroke with the same current waveform parameters are reduced by 10, 9, and 8%, respectively.

In this paper, we have simulated back-flashover at transmission line tower struck by lightning in the presence of corona emanated at the ground wire. In the simulations, three two-circuit 60-m high towers, separated by 400 m, with two overhead ground wires, and six phase conductors (two three-phase circuits) are employed. A simplified (engineering) model of corona discharge is applied to the analysis of transient voltages across insulators of transmission line. Back-flashover is assumed to occur at upper-, middle-, or lower phase. On the basis of computed results, the effect of corona space charge emanated from ground wires on transient voltages across insulators in the presence of back-flashover is discussed.

A bipolar cloud-to-ground lightning flash was observed to exhibit two types of polarity reversal associated with the first two strokes separated by a not-unduly-long time interval of 70 ms. The first, negative stroke had a peak current of −101 kA and was followed by a second, positive stroke whose peak current was 16 kA. The latter contained a 122-ms long bipolar continuing current. The first two strokes, including the bipolar continuing current, occurred in the same channel to ground, whose imaged 2D length was 4.2 km. The occurrence of positive stroke in the negative-stroke channel is highly unusual. The 2D speed versus height profiles for the negative stepped leader of the first stroke and, for the first time, for the positive leader in the previously conditioned, first-stroke channel were examined and the average speeds were found to be 4.7×105 m/s and 7.2×105 m/s, respectively.

High frequency grounding impedance measurements were conducted at the test site in Huta Poreby during the summer season in 2015. The impedances seen from different locations were measured with the impedance meter AES 1002 at frequencies ranging from 100 Hz to 1 MHz. The obtained impedance vs. frequency characteristics have similar shapes. In the low-frequency range impedance values are almost constant while above tens of kilohertz their values begin to rise and reach a peak at about 200 kHz. Above this frequency impedance values begin to decrease. Additionally, the grounding resistances and surge grounding impedances were measured and analyzed.

Lightning electromagnetic fields in the presence of conducting (grounded) structure having a height of 60 m and a square cross-section of 40 m × 40 m within about 100 m of the observation point are analyzed using the 3D finite-difference time-domain (FDTD) method. Influence of the conducting structure on the two orthogonal components of magnetic field is analyzed, and resultant errors in the estimated lightning azimuth are evaluated. Influences of ground conductivity and lightning current waveshape parameters are also examined. When the azimuth vector passes through the center of conducting structure diagonally (e.g., azimuth angle is 45°) or parallel to its walls (e.g., azimuth angle is 0°), the presence of conducting structure equally influences Hx and Hy, so that Hx/Hy is the same as in the absence of structure. Therefore, no azimuth error occurs in those configurations. When the conducting structure is not located on the azimuth vector, the structure influences Hx and Hy differently, with the resultant direction finding error being greater when the structure is located closer to the observation point.

In this paper, we have computed vertical electric field Ez, and azimuthal magnetic field Hφ at different distances from the vertical lightning channel using the finite-difference time-domain (FDTD) method in the 2D cylindrical coordinate system. The presence of conducting atmosphere up to 110 km above ground level was considered. The fields are computed on the ground surface at distances ranging from 50 to 500 km. One-hop and two-hop skywaves (reflections from the ionosphere) were identified in computed waveforms and used for estimation of apparent ionospheric reflection heights.

This chapter reviews representative applications of the finite-difference time domain method (FDTD) method to lightning electromagnetic pulse and surge simulations. The applications reviewed include lightning electromagnetic fields at close and far distances, lightning surges on overhead power transmission line (TL) conductors and towers, lightning surges on overhead distribution and telecommunication lines, the lightning electromagnetic environment in power substations, and lightning surges in wind-turbine-generator towers. It also includes lightning surges in photovoltaic arrays, the lightning electromagnetic environment in electric vehicles, the lightning electromagnetic environment in airborne vehicles, lightning surges and electromagnetic environment in buildings, and surges on grounding electrodes. When an overhead ground wire of a TL is struck by lightning, corona discharge will occur on this wire. Corona discharge around the ground wire reduces its characteristic impedance and increases the coupling between the ground wire and phase conductors.

A simplified model of corona discharge for finite-difference time-domain (FDTD) computations has been applied to analyzing lightning surges propagating along overhead wires with corona discharge. The FDTD computations simulate the experiments of Inoue and Wagner . In Inoue's experiment, a 12.65-mm radius, 1.4-km-long overhead wire was employed, and in Wagner 's experiment, a 21- or 25-mm radius, 2.2-km-long overhead horizontal wire was employed. The critical electric field on the surface of the 12.65-mm-radius wire for corona initiation is set to E0 = 1.4, 2.4, or 2.9 MV/m, and those for 21- and 25-mm-radius wires are set to E0 = 2.2 and 2.1 MV/m, respectively. The critical background electric field for streamer propagation is set to Ecp = 0.5 MV/m for positive voltage application and Ecn = 1.5 MV/m for negative voltage application. The FDTD-computed waveforms (including wavefront distortion and attenuation at later times) of surge voltages at three different distances from the energized end of the wire agree reasonably well with the corresponding measured waveforms. Also, the FDTD-computed waveforms of surge voltages induced on a nearby parallel bundled conductor agree fairly well with the corresponding measured waveforms.

Lightning-induced voltages on a 738-m long overhead two-wire line have been computed using the 3-D finite-difference time-domain (3-D FDTD) method for solving Maxwell's equations. The 3-D FDTD method employed here uses a subgrid model, in which spatial discretization is fine (cell side length is 0.9 m) in the vicinity of overhead wires and coarse (cell side length is 4.5 m) in the rest of the computational domain. The overhead wires having radii of some millimeters are simulated by placing a wire having an equivalent radius of about 0.2 m (≈0.23 × 0.9 m) in the center of an artificial rectangular prism having a cross-sectional area of (2 × 0.9 m) × (2 × 0.9 m) and the modified (relative to air) constitutive parameters: lower electric permittivity and higher magnetic permeability. Induced-voltage peaks computed at different points along the line for the return-stroke speed of 130 m/μs and ground conductivity of 3.5 mS/m agree reasonably well with the corresponding voltage peaks measured in the rocket-triggered lightning experiment of Baker et al., in 1996.

Effects of lightning channel tortuosity and tilt on lightning electric fields and voltages induced on overhead conductors are examined. Overall inclination of the bottom few hundred meters of the lightning channel can appreciably change both the ground-level vertical electric field at distances less than 1 km or so and induced voltage peak relative to the vertical-channel assumption. Smaller-scale tortuosity is responsible for the fine structure of field and induced voltage waveforms. This fine structure can be pronounced at some hundreds of meters and beyond, but is insignificant at shorter ranges

The distribution of lightning current in the lightning protection system (LPS) and the electrical circuit of two test structures simulating residential buildings was experimentally studied at two research facilities in Florida and in Poland. In Florida, the experiments were conducted using rocket-triggered lightning, and in Poland a mobile current surge generator was employed. The soil in Florida was sandy, while in Poland it was mostly clay. Simulations of lightning current in the LPS and the electrical circuit of each of the test structures were also performed. In this paper, we present results of experiments and numerical modeling of lightning current distribution in different configurations of LPS installed on the test structures at the two sites.

A review of lightning protection concepts introduced by Benjamin Franklin (18th century) and James Clerk Maxwell (19th century) is given. Modern approaches to lightning protection of various structures and systems are discussed. In particular, the widely used electrogeometrical model (one version of which is the Rolling Sphere Method) and the topological shielding are presented. Bonding requirements, needed to avoid side flashes (in air or in the soil), are discussed. Lightning parameters important for lightning protection are reviewed.

A simplified model of corona discharge on overhead wire has been proposed for propagating surge computations using the finite-difference time-domain method. The radial progression of corona streamers from the wire is represented as the radial expansion of cylindrical conducting region whose conductivity is several tens of microsiemens per meter. Two wire radii are considered: 5 and 2 mm, in order to simulate two experimental con- figurations by Noda. The critical electric field on the surface of a 5-mm radius wire for corona initiation is set to E0 = 1.8 or 2.9 MV/m. For a 2-mm radius wire, it is set to E0 = 2.2 MV/m. The critical background electric field necessary for streamer propagation is set to Ecp = 0.5 MV/m for positive voltage application, and Ecn = 1.5 MV/m for negative voltage application. The computed waveform of radial current (including both conduction and displacement currents) agrees well with the corresponding measured waveform. Also, the computed relation between the total charge (charge residing on the wire and emanated corona charge) and applied voltage (qV curve) agrees well with the corresponding measured one, except for relatively low applied voltages. Additionally, the increase of coupling between the energized wire and another one nearby due to corona discharge is well reproduced.

This paper discusses the results of high frequency earthing impedance measurements made on the earthing systems installed at Camp Blanding, Florida. Much of the initial information used to confirm the results obtained from high frequency earthing impedance testers is based on comparison of measured data from specifically designed earthing systems with simulations of the expected response of the grounding system. More recently, testing using devices injecting a surge current into a grounding system was compared with earthing impedance testers measuring selected frequencies of up to 1 MHz. It was found that these devices yielded similar results. The impedance measurements at Camp Blanding were compared with currents measured during triggered lightning testing conducted in 2004 and 2005. Even though the dry porous sand at the site made the measurements difficult and the earthing impedance measurements were made four years and longer after system installation and current measurements, correlation was also found between the measured impedance and the measured current distribution.

Using measured wideband electric field waveforms and the Hertzian dipole (HD) approximation, we estimated peak currents for 48 located compact intracloud lightning discharges (CIDs) in Florida. The HD approximation was used because 1) CID channel lengths are expected to range from about 100 to 1000 m, and in many cases can be considered electrically short and 2) it allows one to considerably simplify the inverse source problem. Horizontal distances to the sources were reported by the U.S. National Lightning Detection Network (NLDN), and source heights were estimated from the horizontal distance and the ratio of electric and magnetic fields. The resultant CID peak currents ranged from 33 to 259 kA with a geometric mean of 74 kA. The majority of NLDN-reported peak currents for the same 48 CIDs are considerably smaller than those predicted by the HD approximation. The discrepancy is primarily because NLDN-reported peak currents are assumed to be proportional to peak fields, while for the HD approximation, the peak current is proportional to the peak of the integral of the electric radiation field. An additional factor is the limited (400 kHz) upper frequency response of the NLDN.

The human–environment interaction in the southern part of the Russian Far East is considered, based on current archaeological, chronological, palaeoenvironmental, zooarchaeological, and archaeobotanical data. The major branches of the economy and its dynamics throughout the final Late Pleistocene and the Holocene are reconstructed on the basis of primary indicators (animal and plant remains from cultural complexes). The main stages in the process of human–environment interaction are distinguished, with principal boundaries at ca. 4500 BP (appearance of hoed agriculture), ca. 3000 BP (beginning of animal breeding), and ca. 1500 BP (emergence of plough agriculture and intensive cattle breeding). In some regions, such as Sakhalin Island and the Kurile Islands, communities of hunter-fisher-gatherers continued to exist for a long time, up to the 17–18th centuries AD. The relationship between cultural (maritime adaptation and agriculture) and natural (climatic coolings and warmings, and sea level changes) processes was not direct, and the palaeoeconomy in the Russian Far East was not environmental-driven; migrations and exchange played a certain role in the introduction of productive economy. The history of human–environment interaction in the region under study is closely related to more general features of this process in greater East Asia.

Towers on mountaintops have more incidence of lightning than towers on the flat ground. Therefore towers on mountaintops are ascribed an effective height that is often considerably larger than the physical height of the tower. In this paper, we review and evaluate the definitions and methods that could be used to estimate the effective height of a given tower on mountaintop and propose a new definition based on an engineering model of lightning attachment. The results can be useful in designing lightning protection of communication/transmission lines and masts on mountaintops.

We show that any lightning return-stroke model with specified longitudinal current distribution can be expressed, using the appropriate continuity equation, in terms of two current components, propagation current and corona current. For lumped-current-source (LCS)-type (transmission-line-type) models, the actual corona current is unipolar and directed radially out of the channel core, while for distributed-current-source (DCS)-type (traveling-current-source-type) models, it is also unipolar but directed into the channel core. The conversion between LCS and DCS return-stroke models alters the actual corona current (if any) of the model. A new formulation for LCS lightning return-stroke models is proposed using corona current and propagation current concepts. This formulation expresses the longitudinal current at height z' as the channel-base current minus the overall longitudinal current change from ground surface to z'. Dynamics of lightning-channel corona sheath surrounding the thin channel core are examined based on LCS and DCS models.

We have compared current distributions along a vertical lightning channel above flat ground excited at its bottom by a lumped current source and electromagnetic field waveforms at different distances from the channel, calculated using the finite-difference time-domain method, for different lightning return-stroke electromagnetic models. The channel representations considered include a vertical, perfectly conducting wire surrounded by air (type 1), a vertical wire in air loaded by additional distributed series inductance L = 2.5 muH/m and distributed series resistance R = 0.5 Omega/m (type 2), a vertical, perfectly conducting wire embedded in dielectric of relative permittivity epsivr = 4 that occupies the entire half space (type 3), a vertical, perfectly conducting wire embedded in a 10-m-radius dielectric cylinder of epsivr = 400 surrounded by air (type 4), and a vertical wire embedded in a 10-m-radius cylinder of epsivr = 5 and relative permeability mur = 5 surrounded by air (type 5). For the type-1 model, the speed of the current wave propagating along the lightning channel is essentially equal to the speed of light, v = c. For type-2, type-3, and type-5 models, v = 0.5 c, and for the type-4 model, v = 0.7 c. Models of types 2 and 5 reproduce the maximum number of characteristic features of electric and magnetic field waveforms observed at distances ranging from 1 to 200 km from natural lightning and at distances ranging from tens to hundreds of meters from rocket-triggered lightning. Modifications of type-2 and type-5 models in which distributed channel resistance is not uniform can reproduce all five characteristic features. The influence of lossy ground with conductivity as low as 0.1 mS/m on vertical electric and azimuthal magnetic fields within about d = 5 km is not significant. The initial peak of vertical electric field at d = 50 km for sigma = 0.1 mS/m is 20% smaller than that for sigma = infin. The 10%-90% rise time at d = 50 km is 5 mus for sigma = 0.1 mS/m versus 1 mus for sigma = infin.

Based on experimental evidence of multiple reflections and modeling, we infer that the so-called compact intracloud lightning discharge (CID) is essentially a bouncing-wave phenomenon. Some tens of reflections may occur at both radiating-channel ends. The reflections have little influence on the overall CID electric field signature (narrow bipolar pulse (NBP) waveform), but are responsible for its fine structure, ldquonoisinessrdquo of d E/dt waveforms, and accompanying HF-VHF radiation bursts.

The results obtained in this study show that as the dart leader tip passes a given point on the defunct return stroke channel the electric field increases within a fraction of a microsecond to valu ...

We examined microsecond- and submicrosecond-scale pulses in electric field records of cloud and cloud-to-ground lightning discharges acquired in summer 2006, in Gainesville, Florida. A total of 12 cloud and 12 ground flashes were analyzed in detail, with the electric field record length being 96 or 200 ms and sampling interval being 4 or 10 ns. The majority of pulses in both cloud and ground discharges analyzed in this study were associated with the initial breakdown process and were relatively small in amplitude and duration. The typical durations were an order of magnitude smaller than tens of microseconds characteristic of “classical” preliminary breakdown pulses. We estimated that 26% of the pulses in the 12 cloud discharges and 22% of the pulses in the 12 cloud-to-ground discharges had total durations less that 1 µs.

In this study, we examine the characteristics of electric field pulse trains that are attributed to preliminary breakdown in negative cloud-to-ground lightning discharges and compare them to those of similar pulse trains associated with attempted cloud-to-ground leaders. The data were acquired in 2006 in Gainesville, Florida. The largest pulses in the train can exceed in magnitude the following first return-stroke pulse. The arithmetic mean pulse duration and interpulse interval for pulse trains in negative cloud-to-ground discharges are 4.8 and 65 mus, respectively. The arithmetic mean pulse duration and interpulse interval for pulse trains in attempted cloud-to-ground leaders are 17 and 73 mus, respectively. This implies that pulse trains in ground discharges contain a larger fraction of ldquonarrowrdquo pulses (apparently disregarded in previous studies), defined here as those with durations equal to or less than 4 mus, than the pulse trains in attempted cloud-to-ground leaders. Submicrosecond-scale pulses are observed as part of pulse trains associated with cloud-to-ground discharges, but not with attempted leaders. We also examine the occurrence of pulses of different duration and amplitude in different parts of the preliminary breakdown pulse train of ground discharges. Pulses with larger durations (>4 mus) tend to occur in the initial part of pulse train.

We present the results of structural lightning protective system (LPS) tests conducted in 2004 and 2005 at the International Center for Lightning Research and Testing (ICLRT) at Camp Blanding, FL. Lightning was triggered using the rocket-and- wire technique, and its current was directly injected into the LPS. The test configurations in 2004 and 2005 differed in the lightning current injection point, number of down conductors, grounding system at the test house, and the use of surge protective devices. The primary objective was to examine the division of the injected lightning current between the grounding system of the test house, and remote ground accessible via the neutral of the power-supply cable. In 2004, the mean value of the peak current entering the electrical circuit neutral in search of its way to remote ground was about 22% of the injected lightning current peak, while in 2005, it was about 59%. For comparison, more than 80% of the injected peak current was observed to enter the electrical circuit neutral in similar 1997 tests at the ICLRT in which a different test house with a different (poorer) grounding system was used (Rakov et al. 2002 [1]). An attempt to model the 2004 and 2005 experiments is presented in a companion paper.