Lightning Discharges Research Articles

Observation of Electrical Alignment Signatures in an Isolated Thunderstorm by Dual‐Polarized Phased Array Weather Radar and the Relationship With Intracloud Lightning Flash Rate

AbstractThe electrical alignment signatures of ice crystals in the middle and upper parts of a thunderstorm have a physical connection with the strong electric fields within the cloud. By taking advantage of the high spatio‐temporal resolution of an X‐band dual‐polarized multiparameter phased array radar, this paper employs negative KDP signatures to investigate the variation of electric fields in an isolated thunderstorm within its evolution, and the relationship between the negative KDP signatures and intracloud (IC) lightning activity. The results show that the radar‐inferred strong electric fields distributed in a region of about 8.5–10 km during the developing stage, then extended from about 10 km to the cloud top during the mature stage, with an increasing IC lightning flash rate before the end of the mature stage. Subsequently, the electric fields weakened associated with a large amount of IC lightning discharges. The qualitative analysis results indicate that the evolution of the radar‐inferred electric fields associated with the upper charge regions is consistent with the electrification process in the isolated thunderstorm, inferred by the IC lighting activity. In addition, there is a tendency for the increased IC lightning rate as the decrease in average composite KDP in the middle and upper layers of the thunderstorm, with a time lag of about 5.5 min between the minimum average composite KDP and the peak IC lightning rate, while a good correlation between the negative KDP volume and the IC lightning flash rate at a lag of approximately 9 min.

Experimental vs. natural fulgurite: A comparison and implications for the formation process

Abstract Fulgurites are glassy structures formed when lightning strikes the ground, causing ground material (e.g., rocks, sediments, or soil) to melt and fuse. While fulgurites are relatively rare, they provide valuable insights into paleoecology and may play a key role in prebiotic chemistry. Despite their significance in nature, understanding the conditions underlying the formation of fulgurites poses severe challenges, as the physical parameters and timing of the fulgurite-generating lightning event still need to be discovered. Here, we use a unique opportunity from the recent in situ discovery of a natural fulgurite still embedded in its protolith. (The natural fulgurite-generating event is visible in the World Wide Lightning Network data.) Using a high-voltage setup, we further compare this natural fulgurite with the experimentally generated fulgurite obtained from the original protolith. The natural and experimental fulgurites exhibit evidence of similar melting sequences and post-melting recrystallization structures. Using Raman spectroscopy applied to the quartz phase transition, we estimate the thermal gradient present in the fulgurite during formation to be a minimum of 1600 °C at the inner wall of the fulgurite and ca. 600 °C at the outer wall of the fulgurite. Those findings suggest that the current responsible for the cloud-to-ground lightning discharges that generated the natural fulgurite lay in the range of 11 960 to 14 473 kA. The state of the experimental fulgurites matched that of the natural fulgurite, validating the experimental option for studying fulgurite generation.

The Generation of Seismogenic Anomalous Electric Fields in the Lower Atmosphere, and Its Application to Very-High-Frequency and Very-Low-Frequency/Low-Frequency Emissions: A Review

The purpose of this paper is, first of all, to review the previous works on the seismic (or earthquake (EQ)-related) direct current (DC) (or quasi-stationary) electric fields in the lower atmosphere, which is likely to be generated by the conductivity current flowing in the closed atmosphere–ionosphere electric circuit during the preparation phase of an EQ. The current source is electromotive force (EMF) caused by upward convective transport and the gravitational sedimentation of radon and charged aerosols injected into the atmosphere by soil gasses during the course of the intensification of seismic processes. The theoretical calculations predict that pre-EQ DC electric field enhancement in the atmosphere can reach the breakdown value at the altitudes 2–6 km, suggesting the generation of a peculiar seismic-related thundercloud. Then, we propose to apply this theoretical inference to the observational results of seismogenic VHF (very high frequency) and VLF/LF (very low frequency/low frequency) natural radio emissions. The formation of such a peculiar layer initiates numerous chaotic electrical discharges within this region, leading to the generation of VHF electromagnetic radiation. Earlier works on VHF seismogenic radiation performed in Greece have been compared with the theoretical estimates, and showed a good agreement in the frequency range and intensity. The same idea can also be applied, for the first time, to seismogenic VLF/LF lightning discharges, which is completely the same mechanism with conventional cloud-to-ground lightning discharges. In fact, such seismogenic VLF/LF lightning discharges have been observed to appear before an EQ. So, we conclude in this review that both seismogenic VHF radiation and VLF/LF lightning discharges are regarded as indirect evidence of the generation of anomalous electric fields in the lowest atmosphere due to the emanation of radioactive radon and charged aerosols during the preparation phase of EQs. Finally, we have addressed the most fundamental issue of whether VHF and VLF/LF radiation reported in earlier works is either of atmospheric origin (as proposed in this paper) or of lithospheric origin as the result of microfracturing in the EQ fault region, which has long been hypothesized. This paper will raise a question regarding this hypothesis of lithospheric origin by proposing an alternative atmospheric origin outlined in this review. Also, the data on seismogenic electromagnetic radiation and its inference on perturbations in the lower atmosphere will be suggested to be extensively integrated in future lithosphere–atmosphere–ionosphere coupling (LAIC) studies.

First observation results of Macao Science Satellite 1 on lightning-induced electron precipitation

AbstractThe mid-energy electron detector (MEED) is a space-borne instrument onboard Macao Science Satellite 1 (MSS-1) dedicated to monitoring the typical charged particle radiation characteristics in the satellite orbit and the process of their occurrence and development, including short bursts of lightning-induced electron precipitation (LEP). This paper presents the first results of the LEP measurements by the MSS-1. 47 LEP events are identified with the routine operation for 3 months since satellite launch, all within the range of 1.5<L<3.0 (where L represents the McIlwain L-parameter), and the causative lightning discharges are definitively geo-located for these LEP events. The LEP events occur within <1 s of the causative lightning and consist of 40–300 keV electrons. A preliminary observation result indicates that, with medium-energy electron detectors, MSS-1 can present in-situ observations of large regions of enhanced background precipitation and reveal their fine spatiotemporal characteristics and spectral signatures. The collaborative VLF ground-based measurements at the Great Wall Station, Antarctica also have a good correspondence with LEP measurements of MSS-1. The observations also imply that lightning activity has a modulation effect on the energetic electron energy-spatial structure.

Effect of conductive carbon black on the lightning strikes resistance of carbon fiber-reinforced epoxy resin

The effect of conductive carbon black (0.5 wt%) on the properties of carbon fiber-reinforced epoxy resin (Rockwell hardness, Charpy impact strength, tensile and flexural properties, electrical conductivity, and resistance to lightning discharges) was investigated. The composites were obtained by the infusion method. A slight decrease in flexural modulus was observed, while the hardness and Young's modulus increased. The resistivity decreased four times. Simulated multiple lightning discharges confirmed the better electrical conductivity of the composite with the addition of conductive carbon black, which resulted in five times decrease in the laminate damage area.

Numerical simulation of reversal point dynamics in intracloud lightning: Back-and-forth promoting effect

Lightning is a self-developing charge transport system that exhibits fundamental manifestations of the macro-scale polarity asymmetry. This asymmetry is tightly connected with peculiarities of the reversal point (the point of zero leader sheath charge or, alternatively, a site where the lightning channel potential coincides with the intracloud one) movement along the leader growth direction. The study presents a stochastic lightning discharge model that is used to analyze the reversal point dynamics. It is shown that the reversal point shifts towards the direction of growth of the dominant leader, i.e. the leader with prevailing peripheral current. The cases of upward and downward directions of the positive leader propagation are considered to study how the difference in altitudes of positive and negative lightning poles influences the mode of reversal point drift. The model predicts that, for the case of an intracloud lightning, the amplitudes of oscillation of reversal point altitude and voltage are of the order of 1 km and 100 MV, respectively, with the reversal point voltage change rate being of the order of 10 MV/ms. The results allow to conclude that the reversal point meandering is a fundamental manifestation of lightning evolution.

Numerical simulations of the region of possible sprite inception in the mesosphere above winter thunderstorms under wind shear

Transient luminous events (TLEs) is the collective name given to mesospheric electrical breakdown phenomena occurring in conjunction with strong lightning discharges in tropospheric thunderstorms. They include elves, sprites, halos, and jets, and are characterized by short lived optical emissions, mostly of red (665 nm) and blue (337 nm) wavelengths. Sprites are caused by the brief quasi-electrostatic field induced in the mesosphere, mostly after the removal of the upper positive charge of the thundercloud by a +CG, and they have been recorded above most of the lightning activity centers on Earth. In wintertime, there are just a few areas where lightning occurs, and of those, sprites have been observed over the Sea of Japan, the British Channel, and the Mediterranean Sea. Unlike their summer counterparts, winter thunderstorms tend to have weaker updrafts and as a result, reduced vertical dimensions and compact charge structures, whose positive and negative centers are located at lower altitudes. These storms are often susceptible to significant wind shear and as a result may exhibit a tilted dipole charge structure and a lateral offset of the upper positive charge relative to the main negative charge. We present results of numerical simulations using a three-dimensional explicit formulation of the mesospheric quasi-electrostatic electrical field following a lightning discharge from a typical mid-latitude winter thunderstorm exhibiting tilt due to wind shear and evaluate the regions of possible sprite inception. Our results show, as numerous observations suggest, that sprites can be shifted a large distance from the location of the parent +CG in the direction of the shear and will occur over a larger region compared with non-sheared storms.

Аномальный грозовой процесс на территории Ростовской области

The work examines the anomalous thunderstorm process that occurred on the territory of the Rostov region on June 27, 2023. This thunderstorm process was observed in other regions of the North Caucasus, but the greatest intensity of thunderstorm activity was observed in the territory of the Rostov region, where the thunderstorm lasted more than a day. The analysis of thunderstorm activity was carried out using data from the lightning direction network of the Federal State Budgetary Institution "High Mountain Geophysical Institute". During the day, about 60,000 lightning strikes were recorded in this territory, of which 7,635 were ground strikes. Of the registered 7635 ground-based lightning discharges in the Rostov region, negative lightning amounted to 6625, and positive lightning – 1010. The share of negative lightning discharges from the total number of ground-based lightning discharges in the specified territory was 87 %. The largest number of negative lightning (more than 70 %) had values up to 20 kA. More than 50 % of positive lightning discharges had values from 21 to 40 kA. The average value of the negative polarity currents was -19.19 kA, and the positive polarity was +39.7 kA. Such a large-scale thunderstorm process is a consequence of regional climate change. When carrying out lightning protection measures for facilities in the Rostov region, it is recommended to take into account abnormal values of thunderstorm activity.

Experimental simulation of the generation of microwave radiation during the interaction of a lightning discharge with an aircraft

On a specialized testing installation — a high-voltage Marx generator, which allows the formation of a spark discharge up to 20 meters long, the process of the impact of lightning radio emission in the microwave range on an aircraft (AC) is simulated. A metal AC model made on a scale of 1:50 was placed in a 9 m long rod-plane spark gap. A positive voltage pulse was applied to the high-voltage electrode from the generator (front 100 μsec, duration 7500 μsec). The generated spark discharge passed through the AC model. It was found that when the spark channel passes through the body of the model, electromagnetic pulses of the microwave range with a duration of less than 500 psec and a rise time of less than 100 psec arise. The measurement of the resulting microwave pulses was carried out using special radio equipment in the subnanosecond range. High-speed photography of the discharge development, carried out synchronously with electromagnetic measurements, showed that microwave pulses (up to 10 GHz) arise at the stage of development of the spark discharge leader in the part of the “high-voltage electrode – insulated model” gap. Such pulses can be considered as a factor dangerous for various AC microwave radio systems, when the AC is struck by lightning, as well as for other objects, including power facilities, which contain equipment with microelectronics. Such microwave pulses can also occur during nearby lightning discharges (for example, in a lightning rod of a power substation), when a powerful streamer corona occurs on devices and wires of ultra-high voltage lines), and when a high-voltage spark discharge occurs when switching equipment (disconnectors, arresters) is triggered. In this case, disruptions are possible in the operation of control equipment (for example, relay protection devices) that contains microelectronics, as well as various communication means available at electric power facilities operating in the microwave range (above 1 GHz).

Propagation effect of lightning electromagnetic field along real ground surface and its validation on correcting lightning location system errors

Artificially triggered lightning experimental data from Guangdong Comprehensive Observation Experimental Base on Lightning Discharge (GCOELD) was applied to analyze the propagation effect of lightning electromagnetic field along the real ground surface. The accuracy of the finite-difference time-domain (FDTD) on correcting lightning location system (LLS) errors was validated compared with the Elevation Model (EM). Results show that the wave-shape and time-delay of electromagnetic fields can be significantly affected when they propagate over the real ground surface. The time-delay of the field waveform become larger with an increasing roughness. The wavefront electric field is enhanced due to the reflection and variant of the wave when lightning waves propagate across the high and sharp terrain. Near the lightning strokes, the peak of vertical electric value decreases significantly with the electrostatic shielding effect. The max time delay calculated by FDTD is 8.34 μs; while that by EM is 6.55 μs. In the selected nine lightning stroke points, eight are positively revised by EM, and five by FDTD. Both FDTD and EM can be used on LLS error revision caused by the real ground surface around GCOELD, although EM is more efficient than FDTD in this case.

Моделирование помех в электронном устройстве при воздействии импульсного магнитного поля с использованием искусственной нейронной сети

Modern electronic means are quite sensitive to electromagnetic interference. At the same time, they must function reliably in the existing electromagnetic environment. Lightning discharges and industrial sources make a significant contribution to the formation of the electromagnetic environment around electronic equipment. In this case, pulsed magnetic fields with microsecond parameters most often arise. The most rational approach to ensuring electromagnetic compatibility of electronic means is the most complete accounting and protection from possible phenomena at the design stage. Different methods for modeling the consequences of exposure to electromagnetic interference have their own advantages and disadvantages. To develop a technique and modeling interference in electronic means based on an artificial neural network using the example of the influence of a pulsed magnetic field a the purpose of this work. A practical technique for calculation the magnitude of interference in electronic means using an artificial neural network the paper proposes. All stages of the technique are described: analysis of the main input parameters affecting the amount of interference in the electronic means; the use of a special experimental stand for measuring interference depending on significant input parameters; choosing the structure and parameters of an artificial neural network to modeling interference; choosing a training method for an artificial neural network; choosing a criterion for assessing the quality of training when solving a regression problem; normalization of training data; training an artificial neural network using measured data; modeling the amount of interference in the communication line of an electronic means when exposed to a pulsed magnetic field; assessment of consequences and selection of methods of protection against interference. As an example, we consider the problem of modeling the amount of interference in a communication line inside an electronic means when exposed to a pulsed magnetic field. The magnetic field has parameters recommended by the requirements of the regulatory document on electromagnetic compatibility of devices. In the problem under consideration, an acceptable discrepancy in results is achieved with an acceptable number of neural network training epochs.

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.

Identification of Lightning Discharge Parameters by Its Effect on Fiber-Optic Communication Lines

Identification of Lightning Discharge Parameters by Its Effect on Fiber-Optic Communication Lines

A Lightning Classification Method Based on Convolutional Encoding Features

At present, for business lightning positioning systems, the classification of lightning discharge types is mostly based on lightning pulse signal features, and there is still a lot of room for improvement. We propose a lightning discharge classification method based on convolutional encoding features. This method utilizes convolutional neural networks to extract encoding features, and uses random forests to classify the extracted encoding features, achieving high accuracy discrimination for various lightning discharge events. Compared with traditional multi-parameter-based methods, the new method proposed in this paper has the ability to identify multiple lightning discharge events and does not require precise detailed feature engineering to extract individual pulse parameters. The accuracy of this method for identifying lightning discharge types in intra-cloud flash (IC), cloud-to-ground flash (CG), and narrow bipolar events (NBEs) is 97%, which is higher than that of multi-parameter methods. Moreover, our method can complete the classification task of lightning signals at a faster speed. Under the same conditions, the new method only requires 28.2 µs to identify one pulse, while deep learning-based methods require 300 µs. This method has faster recognition speed and higher accuracy in identifying multiple discharge types, which can better meet the needs of real-time business positioning.

High Peak Current Lightning and the Production of Elves

AbstractElves are observed as expanding rings of light in the UV and visible optical bands. They are produced when electromagnetic pulses from lightning discharges interact with the lower parts of the ionosphere. Elves are well known to be associated with high peak current lightning discharges. Here, we use data from the Modular Multi‐spectral Imaging Array (MMIA) of the Atmosphere‐Space Interactions Monitor (ASIM), and search for observations of Elves when high peak current lightning discharges are detected by Vaisala's Global Lightning Detection network GLD360. We present two groups of events; high peak current detections associated with Elves and high peak current detections not associated with Elves. To understand why some current pulses with high peak currents do not produce observable Elves, we investigate and compare the lightning activity occurring before these two types of events, in terms of both the number of lightning discharges detected by GLD360 and the peak currents of the preceding discharges. Our results, using data from GLD360, suggest that current pulses with peak currents above |120| kA tend to produce Elves nearly always, regardless of the preceding lightning activity. For current pulses with peak currents between |70| and |120| kA, the number of observed Elves might be affected by the preceding lightning activity, or is the result of the characteristics of the storm cells that produce the Elve.

Аномальный грозовой процесс на территории Ставропольского края

The paper analyzes the dynamics of such anomalous weather phenomenon as a thunderstorm. The thunderstorm process that took place in the North Caucasus on June 27, 2023 is considered. The thunderstorm process under consideration differed significantly from the statistical average, both in duration and in lightning parameters. The analysis was carried out using the example of the Stavropol Krai, although anomalous thunderstorms on June 27, 2023 also occurred in other regions of the North Caucasus. The work used the lightning direction network of the Federal State Budgetary Institution VGI with spatially separated sensors LS8000 and LS7002. To determine the characteristics of thunderstorm activity, the work used long-term data from the specified lightning direction network. Studies of thunderstorm activity were carried out in conjunction with the characteristics of convective clouds determined by MRL-5 weather radars. The Federal State Budgetary Institution VGI has organized the uptake, processing, archiving and transmission to the ASPD network of Roshydromet of radar information from all MRL-5 weather radars of the anti-hail services of the North Caucasus. During the day, about 30,000 lightning strikes were recorded by VGI in this territory. Of these, 3,713 were ground discharges. Of the registered 3,713 ground-based lightning discharges in the Stavropol Krai, negative lightning amounted to 2,901, and the positive one – 812. The share of negative lightning discharges from the total number of ground-based lightning discharges in the specified territory was 78%. The largest number of negative lightning (more than 70%) had values up to 20 kA. More than 40% of positive lightning discharges had values from 21 to 40 kA. The average value of currents of negative polarity was -18.6 kA, and that of positive polarity was +53.2 kA.

Understanding the Effects of Aerosols on Electrification and Lightning Polarity in an Idealized Supercell Thunderstorm via Model Emulation

AbstractAerosol effects on the lightning intensity and polarity of a continental supercell storm were investigated using a three‐dimensional lightning scheme within the Weather Research and Forecasting model. We find that both intra‐cloud (IC) and cloud‐to‐ground (CG) flashes are enhanced by the increasing number of cloud condensation nuclei (CCN), especially the percentage of positive CG (+CG) strokes peaking at 42%. Electrical characteristics of the storm varied in different aerosol scenarios through microphysical processes. Added aerosols increase the number of cloud droplets and ice‐phase hydrometeors. The greater ice‐crystal concentration and larger graupel size ensure sufficient charge separation, leading to higher charge density and more lightning discharges. In addition, an inverted polarity charge structure with a strong positive‐charge region in the mid‐levels was formed mainly due to the positively charged graupel in the presence of higher supercooled cloud water content. Positive lightning channels originating from this positive‐charge region propagated to the ground, producing more +CG strokes. When the aerosol concentration was low, the charge density in the upper positive‐charge region was much lower due to smaller ice‐particle content. Consequently, there were barely any +CG strokes. Most of the negative CG flashes deposited positive charge in the lower negative‐charge region.

Retracted: Numerical Simulation and Active Protection of Lightning Discharge Based on Quantum Heuristic Evolutionary Algorithm

Retracted: Numerical Simulation and Active Protection of Lightning Discharge Based on Quantum Heuristic Evolutionary Algorithm

Various Types of Lightning Observed in Mountainous Region Recorded from Kathmandu, Nepal

Vertical electric fields of lightning, generated by thunderstorms manifest on the rugged terrain in the mountainous vicinity of Kathmandu, Nepal. Diverse forms of lightning occurrences have been meticulously documented from a hill station in Kathmandu spanning a three-year interval, commencing from 2015 through 2017. Throughout this duration, cloud-to-cloud lightning discharges constituted 62.8% of the occurrences, while cloud-to-ground lightning discharges accounted for 20.4%. Additionally, 9.5% of the observed events were characterized as unusual lightning phenomena, and 2.9% were attributed to breakdown events. The elevated hills and tall structures inherent to the mountainous landscape significantly influence lightning activity, contributing to a heightened frequency of ground flashes in contrast to other areas.

Toward an Interpretable CNN Model for the Classification of Lightning‐Produced VLF/LF Signals

AbstractAn interpretable convolutional neural network model is proposed for the classification of very low frequency and low frequency lightning electric field waveforms. This model adopts multi‐scale convolutional kernels and shortcut connections to enhance the ability of lightning waveform classification. Based on the data recorded from five provinces in China, the proposed model achieves an accuracy of 98.56% for a four‐type classification task including return strokes, the intra‐cloud lightning, preliminary breakdown, and narrow bipolar events. The proposed model is validated with another open‐source data set from Argentina with an accuracy of 98.45%, which shows good robustness. To ensure the classification, the features learned by the model are visualized. The class activation mapping (CAM) method is adopted to visualize the class‐specific contribution of different waveform parts by using the feature maps of the final convolutional layer. It is highlighted by the CAM method that the proposed model focuses on waveform parts that align with those areas of interests identified by human experts. The high‐contribution waveform parts are furtherly analyzed, which indicate that the proposed model possesses the capability to associate waveform features with the corresponding lightning discharge processes.