Lightning Research Articles

Installation and initial measurement results of the Rogowski-coil-based wind turbine lightning current waveform measurement system

This paper introduces a lightning current waveform measurement system developed at the University of Zagreb's high-voltage laboratory. It details the installation process and initial measurements of the prototype, which was deployed on a wind turbine in the southern part of Croatia, an area prone to winter lightning activity. The system employs two Rogowski coils - one high-frequency, high-amplitude (1 MHz, ±250 kA) and one low-frequency, low-amplitude (10 kHz, ±12.5 kA) - both fixed with magnets near the base of the wind turbine tower. The system efficiently captures both continuing-type currents, such as initial continuous currents, and pulse-type currents, such as return strokes and superimposed impulses. A detailed analysis of a typical upward lightning strike highlights the challenges in waveform measurement, including issues like 2-MHz oscillations in high-frequency sensor measurements and DC offsets in low-frequency sensor measurements. Validation against lightning location system data confirms the overall effectiveness of the current measurements, with the return stroke timestamps matching within the millisecond range.

Virtual Reflection Height of Nighttime Equatorial Ionosphere Estimated With Low‐Frequency Magnetic Sferics Measured in Malacca

AbstractThe return stroke of cloud‐to‐ground (CG) lightning is an impulsive radiator of very low‐frequency/low‐frequency (VLF/LF) electromagnetic signals allowing for the remote sensing of lower ionosphere over large spatial coverage. In this study, we examined the LF magnetic fields measured in Malacca, Malaysia, to probe reflection heights of the lower ionosphere near the equator on three different nights in 2021. The results show that the virtual ionospheric height at nighttime typically ranged from 82.0 to 90.0 km, with a mean value of 85.3 km. Our measurements also revealed significant variations in the virtual ionospheric height across different regions over a spatial scale of about 800 km. The maximum height difference was about 5.0 km. Moreover, the fluctuation characteristics are observed in both estimated ionospheric height and calculated peak reflection ratio during similar periods. This fluctuation may be related to atmospheric gravity waves in the nighttime ionosphere. In addition, we compared the virtual ionospheric height estimated from CG strokes of different polarities, and the results showed that the virtual reflection height for positive CG strokes is lower than that for negative ones.

Effects of urbanization on cloud-to-ground lightning strike frequency: a global perspective.

Urbanization tends to increase local lightning frequency (i.e. the 'lightning enhancement' effect). Despite many urban areas showing lightning enhancement, the prevalence of these effects is unknown and the drivers underlying these patterns are poorly quantified. We conducted a global assessment of cloud-to-ground lightning flashes (lightning strikes) across 349 cities to evaluate how the likelihood and magnitude of lightning enhancement vary with geography, climate, air pollution, topography and urban development. The likelihood of exhibiting lightning enhancement increased with higher temperature and precipitation in urban areas relative to their natural surroundings (i.e. urban heat islands and elevated urban precipitation), higher regional lightning strike frequency, greater distance to water bodies and lower elevations. Lightning enhancement was stronger in cities with conspicuous heat islands and elevated urban precipitation effects, higher lightning strike frequency, larger urban areas and lower latitudes. The particularly strong effects of elevated urban temperature and precipitation indicate that these are dominant mechanisms by which cities cause local lightning enhancement.

A comprehensive evaluation of lightning location accuracy using a weighted gridding method

For the newly built very low-frequency long-range lightning location network (VLF-LLN) in China based on the equivalent propagation velocity method, we have evaluated the probability of deviation distance between the locations results and the reference points by using a weighted gridding method, and have drawn some conclusions. (1) By analyzing the effects of different numbers and configurations of stations on the location deviations, it is found that when the number of participating stations increase, the location deviation relatively decreases, and the numbers and configurations of participating stations has much more effect on the probability of location deviation of the lightning flashes outside the network than those in the network; (2) We statistically analyzed the location deviation for each grid of the network by using a weighted gridding method. The deviation probability using 11-station synchronization as a reference is similar to that for 13-station synchronization per grid. Assuming that the deviation distance is less than 3–5 km, the average location results are almost unchanged when the station number exceeds 7 or 8; (3) Comparing with the Advanced Direction and Time-of-Arrival Detecting network (ADTD), our VLF-LLN has an average deviation value of 3.47 km and a median value of 1.81 km for 63767 lightning flashes, and 90% samples have the location deviation less than 8 km and 54% have the location deviation less than 2 km.

Investigation of positive streamers in CO2: experiments and 3D particle-in-cell simulations

Abstract We investigate the propagation of positive streamers in CO2 through 3D particle-in-cell simulations, which are qualitatively compared against experimental results at 50 mbar. The experiments show that CO2 streamers are much more stochastic than air streamers at the same applied voltage, indicating that few electrons are available in front of the streamer head. In the simulations, we include a photoionization model for CO2. The computational results show that even a small amount of photoionization can sustain positive streamer propagation, but this requires a background electric field close to the critical field. When we compare streamers in CO2 and in air at the same applied voltage, the electric field at the streamer head and the electron density in the streamer channel are higher in CO2. We discuss the uncertainties in CO2 photoionization and provide an estimate for the quenching pressure, which is based on the radiative lifetime of emitting states and the collision frequency of the gas. Furthermore, a criterion for self-sustained streamer growth in CO2 is presented and compared against simulation results.

Percutaneous Thrombectomy Using a Computer-Assisted Aspiration Device for Deep Vein Thrombosis

PurposeTo demonstrate the safety and effectiveness of a computer-assisted large-bore thrombectomy (CA-LBT) device in aspiration thrombectomy for treatment of deep vein thrombosis (DVT). Materials and MethodsA single-institution retrospective review was performed to include 16 consecutive patients (median age, 51.1 years; range, 19–77 years; 5 men and 11 women) who underwent percutaneous thrombectomy using a 16-F CA-LBT device (Lightning Flash Aspiration System; Penumbra, Alameda, California) for DVT (12 iliofemoral occlusions with or without caval extension [75.0%], 3 axillosubclavian occlusions [18.8%], and 1 caval occlusion [6.3%]) between January 2023 and August 2023. ResultsThrombectomy was performed via the popliteal (n = 10, 62.5%), femoral (n = 3, 18.8%), saphenous (n = 1, 6.3%), brachial (n = 1, 6.3%), and femoral and brachial (n = 1, 6.3%) veins, with a median fluoroscopy time of 17 minutes (range, 7.2–61 minutes) and contrast agent volume of 110 mL (range, 30–175 mL). Restoration of anterograde flow was achieved in all cases (100%, 16/16). Thirteen patients (81.2%) received venoplasty after thrombectomy for residual stenosis. Stents were placed in 7 patients (43.8%). With a median clinical follow-up of 77 days (range, 3–278 days), symptom improvement was achieved among 13 of 15 patients (86.7%) who initially presented with DVT-associated symptoms. Of 14 patients with imaging follow-up, patency was confirmed in 12 (85.7%). Of the 2 patients (14.3%) with complete thrombosis on follow-up imaging, 1 was successfully treated with repeated thrombectomy using CA-LBT technology and the other was treated with systemic anticoagulation. ConclusionsAspiration thrombectomy with this 16-F CA-LBT device may be a feasible option for treatment of proximal or large-volume DVT.

Attachment processes of negative flashes with multiple return strokes to a tall tower observed at close distances

Two downward negative flashes (F1612 & F1613) with multiple return strokes struck to the 356-m Shenzhen Tower were analyzed. The high-speed camera captured upward positive connecting leaders (UCL) for the first strokes of both flashes and two subsequent strokes of F1612. The observations also show that none of the downward negative leader (DNL) completely propagated to the tower tip before the occurrence of the return stroke (RS), so that we inferred that the UCL initiated from the tower tip might exist for each RS of the two flashes. The possible height of the UCL and DNL connecting point above the tower tip for each RS was estimated, which showed a positive correlation to the speed of corresponding DNL. The striking distances estimated for 8 subsequent RSs in F1612 were in a range from 14.6 m to 85.4 m and that for 3 subsequent RSs in F1613 were from 24.2 m to 66.2 m. There was a weak positive linear relationship between the DNL speed and striking distance for subsequent RSs in the two flashes. The DNL speed showed a positive correlation to the peak current of corresponding RS.

Using the space-time evolution spectrum to investigate the transmission characteristics of lightning return stroke current

Exploring the physical characteristics of lightning discharge channels based on spectrum can help to reveal the microscopic mechanism of the discharge process and provide a theoretical basis for lightning protection research. According to the spectra of six cloud-to-ground lightning return stroke processes and plasma conduction theory, we investigated the evolution of the total intensity of ionic and atomic lines in the spectra, conductivity, and other parameters along the discharge channel at different stages of the return stroke. The results show that the intensity of ionic lines in the spectrum present an obvious decaying trend with increasing height along the channel during the initial current-rise phase of the return stroke. In the later stages, the decay of ionic line intensity along the channel height slowed down. The intensity of the atomic lines varied slightly with increasing height along the channel during the entire return stroke process. The different space-time evolution characteristics of the spectral line intensity with different excitation energies reflect the differences in the mechanism of light radiation in the core current-carrying and surrounding thermal channels. The spectral characteristics further confirm that the ionic line with higher excitation energy directly relates to the physical process in the core current-carrying channel, and its intensity can roughly reflect the change in current along the channel. The attenuation of the return stroke current along the channel was mainly manifested in the initial stage of the return stroke. The decay rate of conductivity along the channel height is slower than that of the ionic line intensity throughout the return stroke stage, which is related to the channel diameter, it is another key parameter affecting the current transmission in the discharge channel.

Total lightning signatures in a tornadic thunderstorm over the Pearl River Delta of Southern China

Tornado rises rotating air columns extending from the bottom of cumulonimbus clouds to the ground, often accompanied by strong convection with thunderstorms, hail, and short-term heavy precipitation, which seriously threaten people's lives and property safety. Studying the characteristics of thunderstorm activity during a tornado is crucial for comprehending the atmospheric electrical mechanisms involved in its generation process and developing cooperative methods for tornado warning and forecasting. Based on the VLF/LF total lightning location system and radar echo data, this paper analyzes the spatial-temporal evolution, frequency, polarity, and height of total lightning during a strong tornado (EF3) in the Pearl River Delta region on June 3, 2014. The lightning activity lasted for about 3.5 h, with a total of 41,117 total lightning flashes, of which intra-cloud (IC) flashes accounted for 74.7%, cloud-to-ground (CG) flashes accounted for 21.6%, and narrow bipolar events (NBEs) accounted for 3.7%. Connected-Component Labeling (CCL) algorithm was used to divide the thunderstorm into four stages: initiation, development, maturation, and dissipation, and it was observed that the occurrence of tornadoes was closely related to total lightning activities. The observed characteristics of lightning activity in the tornado are summarized through comparison with other studies.

Observation and simulation of dart leader-M component process in rocket-triggered lightning

Three dart leader (DL)-M components in two double-branch lightning flashes were analyzed through high-speed camera and synchronizing current and electric field data. The downward negative DL with a 2-D development speed of 1.2–1.8 × 106 m/s from the branch outside the main channel forms the M component after being intercepted by the main channel. The current waveform of DL-M component shows a typical “hook-shaped” waveform, and the electric field waveform can be clearly divided into DL part and M component part. The waveform of the DL part decreases slower than that of the M component part. Using current measured at the channel base as input, three models were used to simulate the corresponding electric field. The DL-M model, which takes the leader process into account, gives better modelling results.

Length of Critical Streamers

The concept of equipotential length of positive quasi-stationary streamers is introduced as a criterion for assessing their degree of isolation. The equipotential length of positive critical streamers (streamers moving in the minimum electric field sufficient for the unrestricted propagation of a positive streamer) in the normal atmosphere is defined, both for individual streamers and those forming a thin bundle of streamers. The dependence of the equipotential length of positive quasi-stationary streamers on external field, velocity, radius, and electron concentration in the streamer head is investigated. A criterion is proposed for analytical models of quasi-stationary streamers, providing an additional independent equation to the system of equations describing the dynamics of quasi-stationary streamers, valid only for critical streamers. The insignificance of the influence of electrodes located at a distance greater than its equipotential length from the streamer head on the quasi-stationary streamer is proven, confirming the adequacy of using the equipotential length to assess the isolation of positive streamers.

Recommendations related to the Peak-current distributions in studies of lightning performance of transmission lines based on the range of critical currents associated with Backflashover

The impact of cumulative peak current distributions of first return stroke currents on the calculated lightning performance of transmission lines was addressed. The specific features of distributions obtained from measurements at instrument towers and of enlarged distributions including data of magnetic links, were analyzed. The result of their application to real transmission lines (of 138, 230, 345 and 500 kV and exhibiting different parameters) was determined, in terms of backflashover probability and rate. The use of different distributions resulted in great impact on the calculated performance. This impact depends overall on the range of critical currents, below 90 kA and above 100 kA, in which the behavior of the distributions is quite different. Based on the results, a set of recommendations were presented to support the user on the decision about the distribution to adopt, considering the specific features of the transmission line.

Numerical Simulation of Multibranching Positive and Negative Streamer Discharges Near the Oil-Paper Interface in Dielectric Liquid During Pulsed Voltage

Numerical Simulation of Multibranching Positive and Negative Streamer Discharges Near the Oil-Paper Interface in Dielectric Liquid During Pulsed Voltage

Effects of Electric Field Nonuniformity on DC Positive Streamer Discharge of SF6/N2 Mixed Gas

Effects of Electric Field Nonuniformity on DC Positive Streamer Discharge of SF₆/N₂ Mixed Gas

Technical Aspects of Penumbra Indigo Lightning Flash System for Mechanical Thrombectomy of Pulmonary Embolism: A Comprehensive Review.

To demonstrate the technical aspects of the novel Penumbra Indigo Lightning Flash System (Penumbra, Inc.) for mechanical thrombectomy of pulmonary embolism (PE). The novel Penumbra Lightning Flash catheter is a 16 French (F) sheath-compatible device designed for advanced thrombectomy, especially in the pulmonary arteries. This device has large thrombus burden removal capacity; however, technical nuances are necessary to accomplish more with efficacy pulmonary embolism management. Access sites, pulmonary arteries catheterization technique, thrombectomy device navigation and mechanism of action are described thoroughly. Penumbra Indigo Lightning Flash system for mechanical thrombectomy as other catheter-directed treatments (CDTs) represents a major advance in contemporary PE management. With favorable safety profile and efficacy, CDTs have become an integral component of the multidisciplinary approach to PE care. The article highlights the Penumbra Indigo Lightning Flash System as a significant advancement in mechanical thrombectomy for pulmonary embolism (PE). By detailing technical aspects and procedural nuances, it supports clinicians for improvement in endovascular PE management. The system's integration into multidisciplinary care represents a major step forward, providing an effective alternative to traditional therapies, particularly for high-risk PE patients. This innovation promises to enhance patient outcomes in contemporary PE management.

Grounding grid effective area and impulsive impedance considering statistical–probabilistic characteristics of lightning currents

The grounding grid transient behavior is an important substation design criterion. This behavior is determined through interaction with impulsive currents typical of lightning. Based on the technical literature, the behavior in question is determined considering fixed current waves, with median parameters (peak values and front and tail times etc.). Therefore, important statistical–probabilistic characteristics of lightning currents, such as correlations and statistical regressions, are not included. From this perspective, this paper includes research into the sensitivity of impulsive impedance and effective area values of substation grounding grids in relation to the waveform of currents typical of the first return strokes. The results (original) illustrate significant sensitivity of the grids transient behavior in relation to those mentioned statistical–probabilistic characteristics, considering a wide range of resistivities in both current injection points considered in this study.

A simplified time domain approach to calculate lightning electric fields considering the grounded tower-line-tower (TLT) structure

This study describes a method for calculating electric fields radiated by lightning in the presence of a tower-line-tower (TLT) structure, extending a previous method developed by Rachidi et al. (2002). The method involves using a lattice diagram to analyze current distribution and deriving expressions related to the current distribution along the lightning channel and the TLT structure. Expressions associated with the current distribution along the lightning channel and the TLT structure are derived. The impedances of the towers, the connected overhead grounded wire, and lightning channel were treated as constant values. The subsequent return stroke was analyzed in the paper. The lightning radiated electric fields at an intermediate distance of 15 km considering lightning striking to ground, one single object, and the TLT structure were presented and compared. The directly strike of lightning on a tower plays an important role in the increase of the electric field magnitude, while the neighbored tower and the associated grounded wire contributes to periodical superimpositions on the middle-and-late response of the electric fields. Detail discussion on the influences of the different parameters of the proposed method on the electric fields at 15 km and comparison to the measured data were also presented.

Empirical orthogonal function analysis of lightning flashes over India

Lightning studies are highly focused on spatial and temporal variability in various scales but very limited studies are focused on dominant spatial modes of variability. This study intends to identify the possible spatial modes of climate variability of lightning over India during different seasons and relate them to regional and large-scale climate modes. Empirical orthogonal function analysis of lightning has been carried out and the first three orthogonally independent modes are considered in order to retrieve the maximum variance explained by each mode. To understand the role of remote and local teleconnections on the lightning flash rate (LFR) variability, we have analyzed two Pacific Ocean modes (El Niño Southern Oscillation; ENSO, Pacific Decadal Oscillation; PDO) and two Indian Ocean modes (Indian Ocean Dipole; IOD and Bay of Bengal (BOB) meridional Sea Surface Temperature (SST) gradient). First mode is positively correlated with the warm phase of ENSO and PDO whereas second and third modes are negatively correlated with the warm phase of ENSO and PDO during pre-monsoon, post-monsoon and winter. Reverse is true for the monsoon season due to the shift in walker cell caused by the changes in the location of the heat sources and sinks. A strong positive correlation of IOD and BOB meridional SST gradient with first mode, suggests the vital role of nearby Indian Ocean in explaining the typical lightning flashes over India due to the enhanced zonal and meridional circulation, thereby moisture supply to the Indian subcontinent. The impact of Nino-3.4, IOD and BOB meridional SST gradient on lightning over India further suggest the role of SST in local and remote influence on lightning variability through the distribution and transport of heat and moisture.

Investigating Temporal Characteristics of Polarimetric and Electrical Signatures in Three Severe Storms: Insights from the VORTEX-Southeast Field Campaign

Abstract The dual-polarization radar characteristics of severe storms are commonly used as indicators to estimate the size and intensity of deep convective updrafts. In this study, we track rapid fluctuations in updraft intensity and size by objectively identifying polarimetric fingerprints such as ZDR and KDP columns, which serve as proxies for mixed-phase updraft strength. We quantify the volume of ZDR and KDP columns to evaluate their utility in diagnosing temporal variability in lightning flash characteristics. Specifically, we analyze three severe storms that developed in environments with low-to-moderate instability and strong 0–6-km wind shear in northern Alabama during the 2016–17 VORTEX-Southeast field campaign. In these three cases (a tornadic supercell embedded in stratiform precipitation, a nontornadic supercell, and a supercell embedded within a quasi-linear convective system), we find that the volume of the KDP columns exhibits a stronger correlation with the total flash rate. The higher covariability of the KDP column volume with the total flash rate suggests that the overall electrification and precipitation microphysics were dominated by cold cloud processes. The lower covariability with the ZDR column volume indicates the presence of nonsteady updrafts or a less prominent role of warm rain processes in graupel growth and subsequent electrification. Furthermore, we observe that the majority of cloud-to-ground (CG) lightning strikes a carried negative charge to the ground. In contrast to findings from a tornadic supercell over the Great Plains, lightning flash initiations in the Alabama storms primarily occurred outside the footprint of the ZDR and KDP column objects. Significance Statement This study quantifies the correlation between mixed-phase updraft intensity and total lightning flash rate in three severe storms in northern Alabama. In the absence of direct updraft velocity measurements, we use polarimetric signatures, such as ZDR and KDP columns, as proxies for updraft strength. Our analysis of polarimetric radar and lightning mapping array data reveals that the lightning flash rate is more highly correlated with the KDP column volume than with the ZDR column volume in all three storms examined. This contrasts with previous findings in storms over the central Great Plains, where the ZDR column volume showed higher covariability with flash rate. Interestingly, lightning initiation in the Alabama storms mainly occurred outside the ZDR and KDP column areas, contrary to previous findings.

Temporal characteristics of positive cloud-to-ground flashes from tropical thunderstorms

The occurrence of positive cloud-to-ground (CG) lightning flashes proves to be a challenging task when compared to the negative CG flash which common happen in tropical region. This due to the positively charged clouds to reach higher altitudes to enable the transfer of electrical charges to the Earth's surface. With several sensors that deployed in the Malacca region (2.314077°N, 102.318282°E) such as the wide band fast and slow antenna, magnetic field sensors, and the electric field mill (EFM-100). This research study focuses on the temporal characteristics of positive CG lightning activity in the tropical region during September and October 2021. A total of 203 positive cloud-to-ground flashes were meticulously analyzed in the context of 16 thunderstorm events. Key findings highlight the consistent initiation of positive cloud-to-ground flashes through initial breakdown (IB) pulses, followed by the development of stepped leaders and subsequent return strokes. Notably, most positive cloud-to-ground events (72%) were observed as single strokes and the maximum multiplicity recorded being four subsequent return strokes. Furthermore, the analysis focuses into the temporal aspects of these lightning events, revealing average durations for various parameters, including rise-time (6.26 μs), zero-crossing (26.43 μs), pulse duration of the first RS (139.76 μs), and the interval from the first IB to the first return stroke (134.19 ms). Additionally, the recorded data from the Electric Field Mill (EFM) instruments together with Constant Altitude Plan Position Indicator (CAPPI) radar demonstrate a notable correlation. Specifically, the electric field (E-field) values exhibit a discernible increase when positive cloud-to-ground lightning events are detected near the lightning sensor.