Ground Flash Research Articles

Frequency Spectra Features of Positive Ground Flash Radiation Using Wideband and Narrowband Detecting System

Frequency Spectra Features of Positive Ground Flash Radiation Using Wideband and Narrowband Detecting System

Analysis of lightning activity characteristics and its relationship with precipitation in a strong convective weather process in Jiangsu Province

Based on multi-source observation data such as lightning locator, atmospheric electric field instrument and hourly precipitation data from automatic stations, the lightning characteristics of the strong convective weather process under the influence of the northeast cold vortex in Nanjing Jiangsu Province on 15 June 2020 was analyzed in depth, and the relationship between the lightning activity and the precipitation was obtained. The results show that this strong convective weather process is formed by the cold air from the back of the northeast cold vortex along the front of the high-pressure ridge and the back of the transverse through southward to the middle and lower reaches of the Yangtze River, which makes the cold and warm air currents converge along the south of the Yangtze River to form the heavy precipitation, and is accompanied by the strong lightning activity in the process of this heavy precipitation. The local thunderstorm electric field in Nanjing is mainly characterized by negative increasing type, positive and negative alternating type, and multi-single thunderstorm electric field, and the thunderstorm activity is mainly dominated by negative ground flashes. During this strong thunderstorm, the stronger precipitation periods corresponded to the stronger lightning frequency periods, and the lightning and precipitation fallout areas showed a consistent spatial distribution. The correlation between the lightning activity and precipitation was analyzed by linear fitting, and the correlation between them is 0.946.

Recurrent Lightning Spots: Where Lightning Strikes More Than Twice

AbstractThe expression “lightning never strikes twice” is questioned in this paper because, among the randomness of lightning impacts, some spots are hit even more than twice year after year. This article introduces the recurrent lightning spots (RLS) concept, which are locations periodically impacted by cloud‐to‐ground lightning every consecutive year over a certain period. RLS are investigated in two regimes, with markedly different lightning climatology but similar orography, for 10 consecutive years: Catalonia (North East of Spain, Europe) and Barrancabermeja (North Central Colombia, South America). Results revealed 148 and 916 RLS in Catalonia and Barrancabermeja, respectively. RLS in both regions are typically found to be related to tall structures, mountain peaks, and steep terrain. The method allowed us to identify those tall towers and orographic relief frequently affected by lightning that are not detected with the mere computation of the ground flash density. In the case of Catalonia, some RLS are found offshore. Besides the scientific interest in understanding lightning, the new concept of RLS provides additional and valuable information applicable to lightning protection engineering.

Development of GIS-based Ground Flash Density and its Statistical Analysis for Lightning Performance Evaluation of Transmission Lines in Peninsular Malaysia

Malaysia is one of the world's highest lightning regions, making it an ideal location for studying lightning activities, as they cause many power outages on overhead transmission lines. This study presents ground flash density (GFD) mapping and statistical analysis of lightning flash data in Peninsular Malaysia, which will be used to evaluate the lightning performance of transmission lines. Using Geographical Information System (GIS) software, the GFD map and lightning flash data for statistical analysis were extracted. MATLAB was then used to perform statistical analysis and obtain the probability of peak lightning current using the generalized extreme value (GEV) distribution. This study analyzed six years of lightning flash data from 2012 to 2017 recorded by the Lightning Location System (LLS) and used the Peninsular Malaysia base map from the Department of Survey and Mapping Malaysia (JUPEM). Results show that the GFD mapping approach effectively classifies GFD distribution and identifies areas with high lightning activity. 81% of 4,536,380 lightning flashes were negative polarity, with a higher mean peak current magnitude than positive ones. More lightning activity was observed during the Southwest Monsoon (June-September) and the first Inter-Monsoon season (April-May). Pahang had the most lightning flashes due to its large land area. The GFD map overlaid on the transmission line demonstrated how lightning performance on the transmission line can be assessed. These findings are useful for utility and protection engineers to improve the performance of transmission lines.

Analysis of Inverted Charge Structure and Lightning Activity during the 8.14 Local Hailstorm on the Qinghai–Tibet Plateau

In this paper, the charge structure and lightning activity characteristics of the thunderstorm that occurred on the Qinghai–Tibet Plateau on 14 August 2014 were analyzed using data collected from a three-dimensional (3D) lightning very-high-frequency (VHF) radiation source location system and Doppler weather radar. The analysis results showed that the charge structure of the hailstorm was maintained as an inverted dipole throughout the thunderstorm’s development process. The negatively charged region height was distributed in the 5–7 km range (above ground level (AGL)), and the positively charged region was distributed from 2 to 5 km (AGL). The lightning flash types included only cloud flashes and negative cloud–to–ground (CG) flashes in the hailstorm, and cloud flashes accounted for 93% of the total lightning flashes. Cloud flashes accounted for a high proportion of the total flashes, which may have been related to the deep lower positively charged region observed throughout the thunderstorm process. In the hailstorm development stage, the electric field was dominated by positive polarity. When the hail fell, the electric field changed negatively. When the hail ended, the electric field was dominated by negative polarity. A hail event occurred only once and lasted for a long time in the development stage, but in the mature stage, hail fell many times and every time for only a short time, and in the dissipating stage, hail events also occurred many times and each time for a long time. By comparing the radar echoes of the hailstorm cells and normal thunderstorm cells, we found that the area of the 50 dBZ echo in the hailstorm was small, the occurrence time was late, and the duration was short.

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.

Introducing the Concept of the Volume Lightning Strike Density

This letter introduces the concept of the volume lightning strike density (vLSD) and provides the mathematical framework for transitioning from a 2D to a 3D electrogeometric analysis; this may offer new insights into established methodologies for lightning incidence estimation and risk assessment. The feasibility of the vLSD idea is based on the intensive research conducted on emerging technologies of 3D reconstruction of lightning discharges path. Thus, based on the vLSD concept, a new lightning activity parameter <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">NV</i> (strikes/km3/yr), that is, the average number of lightning strikes with at least one leader branch per cubic kilometer per year in an area, can be quantified in light of the widespread installation of modern lightning discharge recording systems. This work may open new horizons on lightning activity characterization offering an alternative or complementary approach to the traditional concept of the ground flash density, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">NG</i> (flashes/km2/yr); the proposed vLSD concept could also be applied in evaluating the lightning interception efficiency of traditional as well as advanced lightning protection systems especially at critical sites, where enhanced lightning protection is of importance.

OVERVIEW OF FACTORS AFFECTING THE ESTIMATION OF LIGHTNING SHIELDING PERFORMANCE OF OVERHEAD TRANSMISSION LINES

This paper examines the risk of lightning stroke to overhead transmission line. The estimation procedure for the lightning performance of overhead power lines is based on the selected lightning attachment model, available lightning parameter statistics, the transmission tower design and voltage levels, type of overvoltage and other characteristics. In this paper the overview of factors affecting the estimation of lightning shielding performance of overhead transmission lines was performed. Among the factors that can affect the estimation accuracy, one can list insufficiently accurate data on the ground flash density in the area of interest and lack of complete data on statistical distribution of lightning current magnitudes. The paper shows that the influence of wind on the increase in the horizontal exposed distance of the phase conductor is not also taken into account. In this research traditional electro-geometric model was used for estimation of lightning performance of 220 kV overhead power line. Results obtained suggest that swing of suspension insulator strings caused by strong winds may lead to increased risk of lightning shielding failure during thunderstorm. Calculation performed for 3 kA lightning current magnitude shows that at swing angle equal to –1 degree, the horizontal unprotected distance of phase conductor increases by 3.1%, that corresponds to 5.240 m uncovered width. When the swing angle is increased to –5 degree, the uncovered width is increased by 15.8% that corresponds to 5.885 m uncovered width. It is proposed that an increase in the risk of lightning shielding failure as a result of wind load can be accounted by applying an appropriate correction factor in expressions for calculation of shielding failure rate, shielding failure flashover rate, etc. Proposed correction factor should account frequency and strength of wind in the area of transmission line route and depend on transmission line voltage level and tower design. Further efforts should be focused on obtaining and justifying the numerical values ​​of this correction factor.

Correlation analysis of preliminary breakdown and first return stroke process in negative ground flash as a function of Northeast and Southwest monsoon in tropic

The separation duration of Preliminary Breakdown to the First Return Stroke (PB-RS duration) and the ratio between the highest amplitude pulse of Preliminary Breakdown and the first Return Stroke pulse (PB/RS ratio) were successfully used as a tool by many researchers to determine the relationship between lightning ground flashes and physical changes (latitude, regional and thunderstorm). Malaysia is one of the countries with the highest lightning flash density globally, and the occurrences of ground flashes are mainly due to monsoon seasons. Monsoons in Malaysia are Northeast, Southwest, and two transition periods. However, there is no available information to relate the lightning activities in Malaysia under the influence of all monsoon seasons. The above statements motivated our team to present a new statistical analysis of lightning flashes under two seasons' effects (Northeast and Southwest). 83 out of 332 electric radiation field data (fast fields) from six thunderstorms were selected and analyzed. The data was recorded using a 12-bit high-speed transient recorder (HDO 4024) with a resolution of tens of nanoseconds and sampling of 12.5 MS/s. PB/RS ratio between the monsoons is similar to each other. Whereas, the PB-RS separation, has two factors longer during the Southwest monsoon than during the Northeast monsoon. We classified the PB/RS ratio into four categories (&gt;100%, 50-100%, 20-50%, and &lt; 20%) as an indication of the preliminary breakdown strength. It found that the weakest pulse train (PB/RS ratio is less than 20%) has shown a longer duration of PB-RS and produces higher lightning return strokes in a negative ground flash than the strong one. The results in this study could be evident that the lower strength of preliminary breakdown is correlated to a lower Low Positive Charge Region (LPCR), which means the initial breakdown process only requires low energy to break the LPCR. Hence, these features have shown the highest number of stroke counts compared to pronounced ones. However, it would be more remarkable if one could provide bulky data for this specific study.

The Impact of Direct Lightning Strike Damages on PV Modules in a Large Malaysian PV Farm

Many lightning risk analyses avoided considering the role of the PV Module’s aluminium frame as a natural lightning air termination system or if such a role is considered, assumed that the ‘thin’ aluminium frame, would not be damaged from metal melting and evaporation at the point of lightning stroke attachment. Although the IEC 62305 is not lacking in guidance on the use of thin metal sheets as air terminations, this aspect is not considered in PV farm design. To ensure correct inputs into the risk assessment calculation, the evaluation of interception and sizing efficiencies and the damage probabilities of the natural components have to be addressed. A comparative analysis is done between two types of air terminations; the PV-frame LPS and the finial-added LPS. The result indicates that for solar PV farms exceeding a certain size and operating in high ground flash density regions like Malaysia, the finial air termination may out-perform the PV-frame LPS.

Relationship Between Convective Storm Properties and Lightning Over the Western Ghats

AbstractX‐band radar observations are integrated with lightning location network observations to investigate the relationship between convective storm properties and lightning over the Western Ghats during a monsoon season (June–September 2014). Convective storms (cells) were identified using an objective‐tracking method and instantaneous lightning strikes within the radar domain were then linked with observed storms. This spatio‐temporal sampling of individual convective cells and lightning has facilitated process‐based study of electrified convection over the Ghats for the first time. Storm and lightning occurrences are typically high during monsoon onset and withdrawal months of June and September, respectively. A spatial correspondence between deep‐intense storms, lightning, and intense convective cores indicated presence of large hydrometeors in the mixed‐phase region of storm supported by strong updrafts and is essential for lightning. The large‐scale instability that peaked during afternoon hours was a key factor in the formation of deep‐intense storms and lightning. Results show that majority of lightning‐producing storms are located on the leeward side as opposed to the windward side. These storms have deeper top‐heights, larger areas and vertically integrated liquid, and an enhanced hail probability than those devoid of lightning. Warm season convection in the study area is accompanied by the preponderance of negative Cloud to Ground (−CG) flashes over positive Cloud to Ground (+CG) lightning. Storms with +CG features exhibited much higher (&gt;2 times) vertical airmass flux in the mid‐troposphere (6–9 km) than storms without +CG features. Furthermore, for majority of +CG storms, intracloud flash occurrences increased significantly above the freezing level.

A Year-Long Total Lightning Forecast over Italy with a Dynamic Lightning Scheme and WRF

Lightning is an important threat to life and properties and its forecast is important for several applications. In this paper, we show the performance of the “dynamic lightning scheme” for next-day total strokes forecast. The predictions were compared against strokes recorded by a ground observational network for a forecast period spanning one year. Specifically, a total of 162 case studies were selected between 1 March 2020 and 28 February 2021, characterized by at least 3000 observed strokes over Italy. The events span a broad range of lightning intensity from about 3000 to 600,000 strokes in one day: 69 cases occurred in summer, 46 in fall, 18 in winter, and 29 in spring. The meteorological driver was the Weather Research and Forecasting (WRF) model (version 4.1) and we focused on the next-day forecast. Strokes were simulated by adding three extra variables to WRF, namely, the potential energies for positive and negative cloud to ground flashes and intracloud strokes. Each potential energy is advected by WRF, it is built by the electrification processes occurring into the cloud, and it is dissipated by lightning. Observed strokes were remapped onto the WRF model grid with a 3 km horizontal resolution for comparison with the strokes forecast. Results are discussed for the whole year and for different seasons. Moreover, statistics are presented for the land and the sea. In general, the results of this study show that lightning forecast with the dynamic lightning scheme and WRF model was successful for Italy; nevertheless, a careful inspection of forecast performance is necessary for tuning the scheme. This tuning is dependent on the season. A numerical experiment changing the microphysics scheme used in WRF shows the sensitivity of the results according to the choice of the microphysics scheme.

Effectiveness of array of lightning triggering towers as regional lightning protection for transmission lines in areas with strong lightning activity

The strong and frequent lightning activity in Guangdong, China, severely affects the safe operation of the power grid. In this study, the lightning database of Guangdong Power Grid in Foshan from 2008 to 2020 was used to compare the CG lightning activity intensity parameters in the areas of four high towers before and after the towers began operation. The lightning frequency within a certain distance from the high towers and the lightning current amplitude around the high towers were higher after the construction of the towers . The clustering method was used to count the number of strong thunderstorms and ground–flash activity processes. The temporal and spatial variations in the aforementioned parameters were also obtained. The high towers increased the number of strong cloud-to-ground activity processes in their adjacent areas, increased the proportion of cloud to ground activity trajectories close to the towers, and changed the direction of lightning corridors. Moreover, the lightning current amplitude of the cloud to ground CG lightning activity was decreased away from the tower. What is more, from the statistical results of operation data, it can be seen that the number of lightning tripping of transmission lines in the area of the towers is significantly reduced.

Observation of preliminary breakdown and leader propagation characteristics in a negative cloud to ground flash with two strike points

High-speed video and electric field data were used to analyze a preliminary breakdown process and three different types of leader processes in a negative cloud to ground flash with two strike points. The preliminary leader was multi-branched and significantly brighter than the stepped leader, with the speed varying from 1.4 × 106 m/s to 6.4 × 105 m/s in a decreasing trend. Two types of chaotic leaders were proposed and compared. Type 1 chaotic leaders last for approximately 0.3 ms, with speed greater than 107 m/s, and no change in leader type throughout the whole leader process. Type 2 chaotic leaders with a duration of approximately 0.5 ms and speed on the order of 106 m/s transformed into a dart-stepped leader with a continuously decreasing speed in the leader process, and the pulse amplitude of chaotic leaders tended to decrease during the transition. The attenuation of the pulse amplitude in electric field (E-field) and the insufficient amount of charge may be responsible for such a conversion.

ANALYSIS OF APPROACHES FOR ESTIMATING THE LIGHTNING PERFORMANCE OF OVERHEAD TRANSMISSION LINES

Purpose. A review of the current literature, regarding the existing approaches used to estimate the lightning perfor-mance of overhead power lines, was performed. A review of available lightning activity data over India was also per-formed. Methodology. The electro-geometrical model was chosen to analyze the lightning performance of overhead power lines. International normative documents and national standard were used to highlight the main parameters that should to be paid main attention to when estimating lightning performance of overhead power lines. Results. Presently, approaches from IEEE and CIGRE guides can be used for analysis of statistical distributions of lightning current pa-rameters. Further studies are required on thunderstorm days, ground flash density and current parameters statistical dis-tributions for different locations, which will be supportive in performing analysis for Indian power lines. Originality. To graphically analyze the shielding failure mechanism with a help of electro-geometric model, the sketch of real 220 kV double-circuit transmission line tower was used. Using electro-geometric model it was graphically shown how downward lightning leader that propagate from thunderstorm cloud toward ground can finish its path on the overhead shield wire, phase conductor or ground plane. Practical value. Available data on lightning activity over different parts of India are still not enough complete. It is of great importance to obtain reliable statistical data on thunderstorm characteristics in the area of the studied power line route. Measurement techniques based on satellites have limitations in obtaining ground flash density values. Thus, for India there is a need in development of modern lightning detection networks and related studies on lightning characteristics. Conclusions. Future efforts should be focused on obtaining not only the positions and number of lightning strikes to the overhead power line, and calculation of lightning flashover rate parameters, but also the statistical distributions of lightning current values and related overvoltage parameters at the overhead wires and different phase conductors. References 21, figures 4.

Distribution of attempted leader with monsoon seasons and negative cloud-to-ground flashes in Melaka, Malaysia

&lt;p&gt;Ninety (90) waveforms recognized as attempted leader were identified with both positive (84 events) and negative (6 events) initial polarity observed from four consecutive years of data (N=10,206). The positive attempted leader shows no correlation with the number of thunderstorms producing it during monsoon. Meanwhile, the negative attempted leader during monsoon and both polarity of attempted leader (positive and negative) during inter-monsoon shows positive correlation with the number of thunderstorms producing it. In this study, the yearly statistical distribution of negative cloud-to-ground (CG) lightning flashes which were classified as positive preliminary breakdown pulses (214 events) and negative preliminary breakdown pulses (4982 events) in accordance of their preliminary polarity were also presented. In addition, there is no relationship of attempted leader and the initial breakdown of negative ground flash since both mechanisms performed as a negative correlation.&lt;/p&gt;

Control Over Skies: Survivability, Coverage, and Mobility Laws for Hierarchical Aerial Base Stations

Aerial base stations (ABSs) have gained significant importance in the next generation of wireless networks for accommodating mobile ground users and flash crowds with high convenience and quality. However, to achieve an efficient ABS network, many factors pertaining to ABS flight, governing laws and information transmissions must be studied. In this article, multidrone communications are studied in three major aspects, survivability, coverage, and mobility laws, which optimize the multitier ABS network to avoid issues related to intercell interference, deficient energy, frequent handovers, and lifetime. The article includes simulation results of hierarchical ABS allocations for handling a set of users over a defined geographical area. Several open issues and challenges are presented to provide deep insights into the ABS network management and its utility framework.

Analysis on Management Strategy of Lightning Protection in Hunan Distribution Lines

The lightning activity is frequent in Hunan, and frequent lightning activities seriously affect the safe and stable operation of distribution network equipment. The statistical analysis of lightning trip-out in Hunan distribution line is made in this paper. According to the current situation of lightning protection in Hunan distribution lines, the differentiated lightning protection management strategy is proposed, which takes into account the ground flash density and special landform factors. And the field application in the past year shows that the effect of lightning protection is good. However, there are also corresponding management and technical problems in the implementation process. The corresponding solution ideas and suggestions are put forward in this paper based on the fully investigation and the experimentation simulation, which has the certain reference value for further improving the lightning withstand level of hunan distribution lines.

A Methodology for Protection of Trees Against Lightning Strikes as a Measure to Prevent Fires and Loss of Human Life

Some regions may be characterized by a very low annual lightning ground flash density, and yet lightning strikes seem to have been in those areas the cause of widespread wildfires in forested areas. Due to global climate change, these occurrences seem to be an increasing threat. In this article, the authors discuss the withstand capability of trees against lightning and introduce the criteria for the deployment of tree lightning protection systems to protect forested areas, where deemed necessary by the tree risk assessment. This work analytically identifies the critical trunk radius of the tree below which the tree may explode in the case of a lightning strike and ignite the surrounding vegetation. The critical heights of trees requiring lightning protection systems to prevent loss of human life and cultural heritage are also identified.

Evaluation of lightning location using measured induced voltage obtained from distribution power networks

Lightning location is a significant issue in the protection of transmission lines, renewable energy sources, and electrical equipment. In this article, a new technique for the determination of lightning striking points is been proposed. This method is depending on measured values of lightning-induced voltage obtained from distribution power lines in the vicinity of the lightning channel. The proposed method considers lightning location as well as lightning current wave shape at the channel base. It was validated using a number of measured return stroke currents, and the outcomes are debated accordingly. All electromagnetic field components were taken into consideration in the proposed method, and lightning current wave shape was determined in contrast with the other, widely used methods. Evaluated lightning current wave shapes, based on local measured data, can be used to examine and improve existing protection schemes in renewable energy generation farms, transmission lines, and other power sites. Moreover, lightning maps and ground flash density can be obtained from the evaluated lighting location data to be used in lightning risk assessment studies.