Lightning Research Articles

New insight of two kinds of M components in a multi-branch rocket triggered lightning flash

After the first and second return strokes (RSs) of a multi-branch triggered lightning flash, the M component of two different initiation mechanisms burned: (1) Upward leader (UL)-M component, (2) Downward leader (DL)-M component. The UL-M component burned immediately after the RS (about 0.5 ms after the RS). At this time, an UL developing to the cloud generated outside the main channel of the continuous current (CC). With the development of the UL, the M component is formed in the CC channel. The obvious DL process can be observed during DL-M component. The speed of DL is about 2 × 107 m/s, when DL was intercepted by CC channel, M component will generate. The current peak and electric field peak of the UL-M component were larger than those of the DL-M component. It was worth noting that the M component formed by the UL slightly developing to the ground at the head of it did not produce an electric field change at the observation point 2 (1550 m horizontally from the rocket triggered lightning point), which was a result of the combined effect of the positive charge in the branch head and the negative charge in the main channel at the same height. The reflection phenomenon of the M component was also observed in a DL-M component process. The CC in the channel after the RS plays a key role in the formation of the M component. It forms the M component by intercepting the current wave transmitted to the ground from the cloud or the lightning branch.

Direct observations of X-rays produced by upward positive lightning

X-rays have been observed in natural downward cloud-to-ground lightning for over 20 years and in rocket-triggered lightning for slightly less. In both cases, this energetic radiation has been detected during the stepped and dart leader phases of downward negative flashes. More recently, X-rays have also been reported during the dart leader phase of upward negative flashes. In this study, we present the observations of four upward positive lightning flashes from the Säntis Tower (2.5 km ASL) in Switzerland. These consist of the simultaneous records of electric current passing through the tower, and electric field strength and X-ray flux 20 m from the tower base. One of the flashes was captured by a high-speed camera operating at 24,000 frames per second, stills from which are also presented. We detected X-rays during the initial phase of upward negative leader propagation, which can be associated with the leader-stepping process from electric field and current waveforms. To the best of our knowledge, this is the first time that such measurements are reported in the literature. The obtained time-synchronised data confirm that the X-ray emissions detected are associated with the initial steps of the upward negative leader. The frequency and energy of X-ray pulses appear to decrease as functions of time, with pulses disappearing altogether within the first millisecond of the leader initiation. X-ray emission also appears to be correlated with the maximum current-derivative and the electric field change of leader steps, consistent with cold electron runaway. These observations contribute to improving our understanding of upward lightning, which is a primary source of damage to tall structures such as wind turbines and telecommunications towers, as well as aircraft during takeoff and landing.

Employing optical lightning data to identify lightning flashes associated to terrestrial gamma-ray flashes

Terrestrial gamma-ray flashes (TGFs) are bursts of energetic X- and gamma-rays emitted from thunderstorms. The Atmosphere-Space Interactions Monitor (ASIM) mounted onto the International Space Station (ISS) is dedicated to measure TGFs and optical signatures of lightning; ISS LIS (Lightning Imaging Sensor) detects lightning flashes allowing for simultaneous measurements with ASIM. Whilst ASIM measures ∼\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim $$\\end{document}300-400 TGFs per year, ISS LIS detects ∼106\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim 10^6$$\\end{document} annual lightning flashes giving a disproportion of four orders of magnitude. Based on the temporal evolution of lightning flashes and the spatial pattern of the constituing events, we present an algorithm to reduce the number of space-detected flashes potentially associated with TGFs by ∼\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim $$\\end{document} 60% and of associated LIS groups by ∼\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim $$\\end{document} 95%. We use ASIM measurements to confirm that the resulting flashes are indeed those associated with TGFs detected at approx. 400 km altitude and thus benchmark our algorithm preserving 70–80% of TGFs from concurrent ASIM-LIS measurements. We compare how the radiance, footprint size and the global distribution of lightning flashes of the reduced set relates to the average of all measured lightning flashes and do not observe any significant difference. Finally, we present a parameter study of our algorithm and discuss which parameters can be tweaked to maximize the reduction efficiency whilst keeping flashes associated to TGFs. In the future, this algorithm will hence be capable of facilitating the search for TGFs in a reduced set of lightning flashes measured from space.

Statistical analysis on branching characteristics of positive streamer discharges in N2–O2 mixtures

Streamers are fast-propagating ionization channels that can usually branch and form complex tree-like structures in dielectric media. In this paper, we perform experiments on positive streamers in different N2–O2 mixtures under varying conditions including voltage, pressure, and electrode geometry, with at least 125 discharge images captured for each condition. We present a statistical analysis on streamer branching characteristics from 3D models that are reconstructed by stereoscopic stroboscopic images and our dedicated semi-automatic 3D reconstruction method.We found that by varying the concentration of O2, the morphology and branching characteristics are greatly changed. Specifically, the average branching angle decrease significantly from 90∘ in air to 66∘ in 1% O2, suggesting that photoionization plays an important role in streamer branching. The branching angles in our work are generally larger than previously reported results due to the resolved 3D structures of discharges by our method. A linear relation between the streamer diameter ratio and the branching direction difference of two daughter branches is found, which intersects the vertical axis almost at unity. It is also found that the average branching angles, streamer velocities and diameters increase as the voltage increases. This is again attributed to stronger photoionization effect under higher voltages. The velocities and diameters are similar at different pressures but at the same reduced electric field. The average branching angle decreases from 90∘ at 133 mbar to 79∘ at 200 mbar. This suggests that stochastic fluctuations become dominant over photoionization effect at higher pressures.

Dynamic propagation velocity of a positive streamer in a 3 m air gap under lightning impulse voltage

Streamers represent an important stage in the initiation of gap discharge. In this work, we used an eight-frame intensified charge-coupled device camera to capture the streamer development process when a lightning impulse voltage of 95%–100% U 50% was applied in a 3 m rod–plate gap and the streamer velocity was analyzed. Analysis of the observations shows that streamer velocity can be defined by three stages: rapid velocity decline (stage 1), rapid velocity rise (stage 2) and slow velocity decline (stage 3). The effects of electrode shape, applied voltage and gap breakdown or withstanding on streamer velocity were analyzed. The electrode with a larger radius of curvature will result in a higher initial velocity, and a higher voltage amplitude will cause the streamer to propagate faster at stage 3. Gap withstanding or breakdown has no obvious effect on streamer velocity. In addition, the experimental results are compared with previous results and the statistical characteristics of the primary streamer discharge are discussed.

Influence of AC and DC Composite Voltage on Positive Streamer Discharge

Influence of AC and DC Composite Voltage on Positive Streamer Discharge

Evaluating the impact of air terminal geometry on lightning intercept efficacy under a strong background electric field

A comparative analysis of the attachment efficacy of sharpened vs blunted air terminals under a strong background DC electric field, similar to conditions found in naturally occurring lightning events, is presented. Testing was conducted using an oil-free, 17-stage, 1.4 MV bipolar Marx generator with a biased discharge plane that emulated the conditions found prior to the lightning return stroke. The biased discharge plane allowed the introduction of a strong DC electric field and subsequent corona formation on a time scale much longer than the brief duration over which the downward leader propagates. Initial observations indicate that despite a higher background electric field at the sharpened terminals, leading to pre-discharge corona formation where none is seen on the blunt terminal, both the sharpened and blunted terminals exhibit similar attachment probabilities during discharge events, with some discharge events attaching to both terminals.

Imaging of 3 bright terrestrial gamma-ray flashes by the atmosphere-space interactions monitor and their parent thunderstorms

The Atmosphere-Space Interactions Monitor (ASIM) on the International Space Station (ISS) includes an instrument designed to geolocate Terrestrial Gamma-ray Flashes (TGF) produced by thunderstorms. It does so with a coded aperture system shadowing the pixelated Low Energy Detector of the Modular X- and Gamma-ray Sensor (MXGS). Additionally, it locates associated lightning flashes with the Modular Multispectral Imaging Array (MMIA). Here we present 3 bright TGFs with very similar duration, fluency and observation distance. The innovative imaging capabilities allow us to determine the TGF position and correlate the TGF-lightning parent event in time and position simultaneously. The accurate position determination and distance to the observer allow us to perform a comparative study of TGF characteristics. These TGFs were produced in association with lightning flashes below the highest cloud tops of developing to mature convective cells. In one event, GLM (Geostationary Lightning Mapper) cloud flash rates were slowing down after the TGF while negative cloud-to-ground flashes suddenly ceased from 10 to 5 min before the TGF. An 8-stroke (strongest: -93 kA) cloud-to-ground flash occurred 31 s before the TGF. Vertical profiles from the ERA5 reanalysis data suggest TGFs may be produced in variety of tropical environments.

Comparison of Different Models to Simulate Forest Fire Spread: A Case Study

With the development of computer technology, forest fire spread simulation using computers has gradually developed. According to the existing research on forest fire spread, the models established in various countries have typical regional characteristics. A fire spread model established in a specific region is only suitable for the local area, and there is still a great deal of uncertainty as to whether or not the established model is suitable for fire spread simulation for the same fuel in other regions. Although many fire spread models have been established, the fuel characteristics applicable to each model, such as the fuel loading, fuel moisture content, combustibility, etc., are not similar. It is necessary to evaluate the applicability of different fuel characteristics to different fire spread models. We combined ground investigation, historical data collection, model improvements, and statistical analysis to establish a multi-model forest fire spread simulation method (FIRER) that shows the burning time, perimeter, burning area, overlap area, and spread rate of fire sites. This method is a large-scale, high-resolution fire growth model based on fire spread in eight directions on a regular 30 m grid. This method could use any one of four different physical models (McArthur, Rothermel, FBP, and Wang Zhengfei (China)) for fire behavior. This method has an option to represent fire breaks from roads, rivers, and fire suppression. We can evaluate which model is more suitable in a specific area. This method was tested on a single historical lightning fire in the Daxing’an Mountains. Different scenarios were tested and compared: using each of the four fire behavior models, with fire breaks on or off, and with a single or suspected double fire ignition location of the historical fire. The results show that the Rothermel model is the best model in the simulation of the Hanma lightning fire; the overlap area is 5694.4 hm2. Meanwhile, the real fire area in FIRER is 5800.9 hm2; both the Kappa and Sørensen values exceed 0.8, providing high accuracy in fire spread simulations. FIRER performs well in the automatic identification of fire break zones and multiple ignited points. Compared with FARSITE, FIRER performs well in predicting accuracy. Compared with BehavePlus, FIRER also has advantages in simulating large-scale fire spread. However, the complex data preparation stage of FIRER means that FIRER still has great room for improvement. This research provides a practical basis for the comparison of the practicability and applicability of various fire spread models and provides more effective practical tools and a scientific basis for decision-making and the management of fighting forest fires.

Spectroscopic method to study the effect of lightning return stroke channel expansion on atmospheric pressure

Using the plasma radiation spectra of three natural cloud-to-ground multi-strike lightning discharges recorded by a slitless grating spectrograph, and based on the spectral wavelengths and relative intensities, combined with information about the lightning-synchronized ground electric field variations, we calculated the temperatures, line-charge densities, initial radii, and final radii of the lightning-strike channels. This was achieved by applying the theory of air plasma transport, lightning electrodynamics, the laws of conservation of energy and pressure. Subsequently, we determined the initial internal energies of the lightning plasma channels, the final internal energies, the work done by the return stroke channel expansion against atmospheric pressure, equivalent impedances, and the speed of charge movement. The results show that the temperature of the return stroke channel and the work done by the expansion of the return channel on the atmospheric pressure decrease with the development of the return stroke process. The final radius and the initial internal energy, as well as the initial peak electric field and the work done by the return stroke channel expansion on the atmospheric pressure, exhibit a strong linear relationship. The equivalent impedance and speed of charge movement show a nonlinear relationship with the work done by the return stroke channel expansion against atmospheric pressure. The changes in initial internal energy, final internal energy, and the expansion work of the return stroke channel against atmospheric pressure are essentially consistent and positively correlated. The initial peak electric field of the return channel increases, leading to enhanced spectral intensity. The return stroke channel temperature, initial radius, final radius, initial internal energy, final internal energy, and the work done by the return stroke channel expansion against atmospheric pressure all increase. Meanwhile, the equivalent impedance and speed of charge movement decrease.

Estimation of lightning overvoltages and critical flashover currents of 150 kV and 400 kV overhead lines: Effects of the CIGRE lightning current waveform parameters

This paper investigates the influence of the CIGRE lightning current waveform parameters on the computation of fast-front overvoltages and critical lightning currents causing flashover of overhead transmission line insulation. The investigation is conducted via ATP-EMTP simulations employing both negative and positive lightning current waveforms corresponding to first return strokes. Typical 150 kV and 400 kV double-circuit overhead lines are evaluated by performing shielding failure and backflashover simulations. The statistical distributions of the parameters required as input for the CIGRE lightning current waveform (front time, maximum steepness, time to half value) are considered in simulations to quantify and analyze their effects; this enables the comparison between negative and positive lightning strikes. The waveform parameters do not affect considerably the critical shielding failure flashover current for both polarities; the most influential parameter in this case is the time to half value. On the other hand, the wavetail duration influences the least the critical backflashover current; the latter is lower for waveforms with faster wavefront (lower front time and higher maximum steepness). The impact of the waveform parameters of positive lightning strikes is more marked for the backflashover case due to their larger variations compared with negative strikes.

Deicing and status characteristics of dual-side pulsed surface dielectric barrier discharge

The deicing process and its status characteristics of dual-side pulsed surface dielectric barrier discharge (SDBD) are studied via electro-optical diagnostics, thermal properties, and numerical simulation. Experimental results show that the dual-side pulsed SDBD can remove the glaze ice compared to the traditional pulsed SDBD under the applied pulse voltage of 8 kV and a pulse frequency of 1 kHz. The maximal temperature of dual-side pulsed SDBD reaches 39.5 °C under the discharge time of 800 s, while the maximal temperature of traditional pulsed SDBD is still below ice point about −7.8 °C. Surface temperatures of dual-side pulsed SDBD demonstrate that the SDBD with a gap of 1 mm possesses prospects in deicing. The maximal surface temperature reaches 37.1 °C under the pulse of 8 kV after the discharge time of 90 s. Focusing on the thermal effect, a two-dimensional plasma fluid model is implemented, and the results also indicate that the dual-side pulsed SDBD with a gap of 1 mm produces a highest heat density among the three different configurations. Comparing the spatial-temporal evolutions of plasma on both dielectric sides, primary positive streamer has a longer propagation length of 8.6 mm than the secondary negative streamer, the primary negative streamer, and the secondary positive streamer, which induces a long heat covered area. Four stages of deicing process are analyzed through a series of electrical parameters under different covered ice conditions.

Numerical simulation of a positive streamer discharge in a combined gap based on aircraft lightning zoning test

The research involves conducting high voltage tests to determine lightning attachment locations on an aircraft model and constructing a streamer discharge simulation model in a 20 cm combined gap. The investigation focuses on the air streamer discharge of a non-uniform electric field in the combined gap through experiments and numerical simulation. The results reveal that the discharge process in the electrode-aircraft model gap closely aligns with the final jump stage of natural lightning. Notably, the surface charge density on the aircraft model exhibits a negative correlation with the radius of curvature. Due to the enhanced electric field strength, the aircraft model tips with bigger curvatures have a greater likelihood of initiating streamer discharge. Once the streamer bridges the electrode-aircraft model gap, the accumulation of space charge results in the aircraft’s surface charge reaching an order of magnitude higher than the initial induced charge.

Inter-Comparison of Lightning Measurements in Quasi-Linear Convective Systems

Data from four lightning networks collected during three quasi-linear convective systems (QLCS) are used to understand the differences in detection for optimizing their combined use. Additionally, using unique aspects from each network provides a more complete picture of lightning in a thunderstorm. The four lightning networks examined include a Lightning Mapping Array (LMA), the Earth Networks Total Lightning Network (ENTLN), the Geostationary Lightning Mapper (GLM), and the National Lightning Detection Network (NLDN). The data from each network are inter-matched and locations where each network uniquely detected a flash versus all are analyzed in reference to three QLCSs, including two QLCSs that occurred in the Southeast (22 March 2022 and 30 March 2022) during the Propagation, Evolution, and Rotation in Linear Systems (PERiLS) field campaign, and one case from Oklahoma (26 February 2023). Unique aspects of the lightning provided by each network are examined, including flash initiation altitude, size, type, and energy. Lightning flash trends and characteristics for each QLCS are similar between networks in general, but deviate in certain conditions and locations. Times of decreased matching between networks were associated with localized increases in lightning rates, smaller flash sizes, and lower-energy flashes. The differences in each network’s performance across the QLCSs demonstrates the importance of understanding the limitations in each and the advantage of using multiple networks.

Stochastic and self-consistent 3D modeling of streamer discharge trees with Kinetic Monte Carlo

This paper contains the foundation for a new Particle-In-Cell model for gas discharges, based on Îto diffusion and Kinetic Monte Carlo (KMC). In the new model the electrons are described with a microscopic drift-diffusion model rather than a macroscopic one. We discuss the connection of the Îto-KMC model to the equations of fluctuating hydrodynamics and the advection-diffusion-reaction equation which is conventionally used for simulating streamer discharges. The new model is coupled to a particle description of photoionization, providing a non-kinetic all-particle method with several attractive properties, such as: 1) Taking the same input as a fluid model, e.g. mobility coefficients, diffusion coefficients, and reaction rates. 2) Guaranteed non-negative densities. 3) Intrinsic support for reactive and diffusive fluctuations. 4) Exceptional stability properties. The model is implemented as a particle-mesh model on cut-cell grids with Cartesian adaptive mesh refinement. Positive streamer discharges in atmospheric air are considered as the primary application example, and we demonstrate that we can self-consistently simulate large discharge trees.

Mechanisms of charge-induced surface discharge under positive impulse voltages

Abstract Charge-induced surface flashover is a critical factor leading to insulation failures in high-voltage direct current gas-insulated equipment, and the underlying mechanisms are still unclear. In the present study, the typical surface charge distributions are first summarized. Then, the impact of charge polarity and position on surface discharge characteristics in ambient air is studied, and the surface charge dynamics during multiple discharge processes are also focused. Comparative studies of the charge-induced surface discharge are conducted in SF6, and the effect of the gas atmosphere is discussed. The results indicate that the repulsive effect of deposited positive charges significantly inhibits the positive streamer development by reducing the electric field. The acceleration of negative charges on positive streamer propagation is the result of two competitive mechanisms: the enhancement of the electric field and the neutralization with positive charges in the streamer channel. In the multiple discharge process, positive streamers develop along the gap of positive streamer channels from the previous discharge. When the last discharge is intense enough, back discharges may occur along the pattern of the deposited positive channels from the previous discharge. The effects of the deposited charges on the surface discharge process are consistent in air and SF6. These findings will be advantages in improving the insulation reliability of gas-insulated equipment.

FDTD-based computational model applied to assess the influence of the frequency dependence of soil parameters on the lightning response of grounding electrodes for typical parameters of first and subsequent return stroke currents

This paper considers an evaluation of the influence of the frequency-dependence of soil parameters on the lightning response of horizontal grounding electrodes by means of the finite-difference time domain (FDTD) electromagnetic model. The FDTD simulations assumed the soil modeled as a multipole Debye medium and the response of grounding electrodes due to lightning return stroke currents with typical front time parameters of negative first and subsequent strokes was assessed. The results in terms of the ground potential rise (GPR) and grounding impulse impedance (ZP), were compared to those provided by the application of the Hybrid Electromagnetic Model (HEM), a frequency domain model widely applied for lightning related problems, and revealed the top quality of the modeled approach in FDTD. The largest percentage variations of the calculated impulse impedance compared to HEM were around 6 % and 10 % for first and subsequent stroke currents, respectively.

A 3D kinetic Monte Carlo study of streamer discharges in CO2

We theoretically study the inception and propagation of positive and negative streamers in CO2 . Our study is done in 3D, using a newly formulated kinetic Monte Carlo discharge model where the electrons are described as drifting and diffusing particles that adhere to the local field approximation. Our emphasis lies on electron attachment and photoionization. For negative streamers we find that dissociative attachment in the streamer channels leads to appearance of localized segments of increased electric fields, while an analogous feature is not observed for positive-polarity discharges. Positive streamers, unlike negative streamers, require free electrons ahead of them in order to propagate. In CO2 , just as in air, these electrons are supplied through photoionization. However, ionizing radiation in CO2 is absorbed quite rapidly and is also weaker than in air, which has important ramifications for the emerging positive streamer morphology (radius, velocity, and fields). We perform a computational analysis which shows that positive streamers can propagate due to photoionization in CO2 . Conversely, photoionization has no effect on negative streamer fronts, but plays a major role in the coupling between negative streamers and the cathode. Photoionization in CO2 is therefore important for the propagation of both positive and negative streamers. Our results are relevant in several applications, e.g. CO2 conversion and high-voltage technology (where CO2 is used in pure form or admixed with other gases).

3D simulations of positive streamers in air in a strong external magnetic field

We study how external magnetic fields from 0 to 40 T influence positive streamers in atmospheric pressure air, using 3D PIC-MCC (particle-in-cell, Monte Carlo collision) simulations. When a magnetic field B is applied perpendicular to the background electric field E , the streamers deflect towards the +B and −B directions which results in a branching into two main channels. With a stronger magnetic field the angle between the branches increases, and for the 40 T case the branches grow almost parallel to the magnetic field. Due to the E×B drift of electrons we also observe a streamer deviation in the opposite −E×B direction, where the minus sign appears because positive streamers propagate opposite to the electron drift velocity. The deviation due to this E×B effect is smaller than the deviation parallel to B . In both cases of B perpendicular and parallel to E , the streamer radius decreases with the magnetic field strength. We relate our observations to the effects of electric and magnetic fields on electron transport and reaction coefficients.

TGFs, Gamma‐Ray Glows, and Direct Lightning Strike Radiation Observed During a Single Flight of a Balloon‐Borne Gamma‐Ray Spectrometer

AbstractTerrestrial gamma‐ray flashes (TGFs) and other high‐energy radiation phenomena related to thunderstorms remain incompletely understood since their discovery nearly 30 years ago. Space and ground‐based platforms have provided insights, but limitations exist in temporal resolution, signal‐to‐noise ratios, and proximity to events. This study presents findings from a balloon‐borne gamma‐ray spectrometer flown into a thunderstorm over northern Mississippi on 19 June 2023. The instrument detected three distinct millisecond‐duration TGF events correlated with lightning strikes. Sustained gamma‐ray glows lasting up to 2 minutes were measured and tied to thunderstorm electrostatic fields. Notably, radiation was observed during a direct lightning strike to the payload. This complex 800‐millisecond event reveals insights into radiation from leader propagation and return strokes. These findings from a single balloon flight demonstrate the prevalence of energetic processes within thunderstorms. Finally, the balloon platform offered an exceptional combination of temporal resolution and validation capabilities to advance the understanding of thunderstorm radiation motivating future follow‐up studies.