Ground Strike Points Research Articles

Insights into ground strike point properties in Europe through the EUCLID lightning location system

Abstract. Evaluating the risk of lightning strikes to a particular structure typically involves adhering to the guidance outlined in IEC 62305-2. Among the multitude of factors influencing the overall risk, flash density emerges as a crucial parameter. According to its definition, each flash is assigned only one contact point to ground. Nevertheless, it is well known that, on average, flashes exhibit multiple ground termination points as shown by high-speed camera observations. In this research, lightning data collected by the European Cooperation for Lightning Detection (EUCLID) network are utilized in combination with a ground strike point (GSP) algorithm that aggregates individual strokes within a flash into ground strike points. This approach enables the examination of spatio-temporal patterns of GSPs across Europe throughout a decade, spanning from 2013 to 2022. Average GSP densities exhibit variations across the European continent, mirroring the observed patterns in flash densities. The highest densities are concentrated along the Adriatic Sea and the western Balkan region, reaching peak values of up to 8.5 GSPs km−2 yr−1. The spatial distribution of the mean number of ground strike points per flash reveals a noticeable increase in the Mediterranean, Adriatic, and Baltic Sea regions compared to inland areas. Moreover, it has been determined that the average number of GSPs per flash reaches its peak between September and November. Additionally, a daily pattern is discernible, with the lowest number of GSPs per flash occurring between 12:00 and 18:00 UTC (universal time coordinated). It is found that 95 % of the separation distances between distinct GSPs are less than 6.7 km. Lastly, it is worth noting that the presence of the Alps has an impact on GSP behaviour, resulting in lower GSP counts in comparison to the surrounding areas, along with the shortest average distances between different GSPs.

Analyses of negative cloud-to-ground flashes and their ground strike points in Austria

Analyses of negative cloud-to-ground flashes and their ground strike points in Austria

Global ground strike point characteristics in negative downward lightning flashes – Part 1: Observations

Abstract. Information about lightning properties is important in order to advance the current understanding of lightning, whereby the characteristics of ground strike points (GSPs) are in particular helpful to improving the risk estimation for lightning protection. Lightning properties of a total of 1174 negative downward lightning flashes are analyzed. The high-speed video recordings are taken in different regions, including Austria, Brazil, South Africa and the USA, and are analyzed in terms of flash multiplicity, duration, interstroke intervals and ground strike point properties. According to our knowledge this is the first simultaneous analysis of GSP properties in different regions of the world applying a common methodology. Although the results vary among the data sets, the analysis reveals that a third of the flashes are single-stroke events, while the overall mean number of strokes per flash equals 3.67. From the video imagery an average of 1.56 GSPs per flash is derived, with about 60 % of the multiple-stroke flashes striking the ground in more than one place. It follows that a ground contact point is struck 2.35 times on average. Multiple-stroke flashes last on average 371 ms, whereas the geometric mean (GM) interstroke interval value preceding strokes producing a new GSP is about 18 % greater than the GM value preceding subsequent strokes following a pre-existing lightning channel. In addition, a positive correlation between the duration and multiplicity of the flash is presented. The characteristics of the subset of flashes exhibiting multiple GSPs is further examined. It follows that strokes with a stroke order of 2 create a new GSP in 60 % of the cases, while this percentage quickly drops for higher-order strokes. Further, the possibility of forming a new lightning channel to ground in terms of the number of strokes that conditioned the previous lightning channel shows that approximately 88 % developed after the occurrence of only one stroke. Investigating the time intervals in the other 12 % of the cases when two or more strokes re-used the previous lightning channel showed that the average interstroke time interval preceding a new lightning channel is found to be more than twice the time difference between strokes that follow the previous lightning channel.

Global ground strike point characteristics in negative downward lightning flashes – Part 2: Algorithm validation

Abstract. At present the lightning flash density is a key input parameter for assessing the risk of occurrence of a lightning strike in a particular region of interest. Since it is known that flashes tend to have more than one ground termination point on average, the use of ground strike point densities as opposed to flash densities is more appropriate. Lightning location systems (LLSs) do not directly provide ground strike point densities. However, ingesting their observations into an algorithm that groups strokes into respective ground strike points results in the sought-after density value. The aim of this study is to assess the ability of three distinct ground strike point algorithms to correctly determine the observed ground-truth strike points. The output of the algorithms is tested against a large set of ground-truth observations taken from different regions around the world, including Austria, Brazil, France, Spain, South Africa and the United States of America. These observations are linked to the observations made by a local LLS in order to retrieve the necessary parameters of each lightning discharge, which serve as input for the algorithms. Median values of the separation distance between the first stroke in the flash and subsequent ground strike points are found to vary between 1.3 and 2.75 km. It follows that all three of the algorithms perform well, with success rates of up to about 90 % to retrieve the correct type of the strokes in the flash, i.e., whether the stroke creates a new termination point or follows a pre-existing channel. The most important factor that influences the algorithms' performance is the accuracy by which the strokes are located by the LLS. Additionally, it is shown that the strokes' peak current plays an important role, whereby strokes with a larger absolute peak current have a higher probability of being correctly classified compared to the weaker strokes.

Simulation of cloud-to-ground lightning strikes to structures based on an improved stochastic lightning model

An improved stochastic method for computer simulation of lightning leaders is developed based on the results from optical observation data. The development and attachment process of downward negative cloud-to-ground lightning in the near-ground area is simulated. The distribution of lightning strike points influenced by tall structures is statistically analyzed. The results show that when downward negative leaders initiate at 1500 m height over a structure, the relative strike frequency for the structure increases at a decreasing rate as the structure height increases. The strike frequency for a 600 m tall structure is approximately 3.6 times that for a 100 m tall structure. Additionally, the structure may attract some lightning to hit itself and shift nearby ground strike points toward the structure. For taller structures, the deviation effect is more apparent. It is stipulated in this study that if the ground strike density in the vicinity of the structure is no more than 5% of the average density, then the structure has a sufficient protective effect on this area. The data indicate that there is a positive correlation between the protection distance and the height of the structure. The protection distances of structures of 100–600 m in height are 200 m, 280 m, 350 m, 400 m, 450 m, and 480 m approximatively, which show a declining rate of increase.

Characteristics of Negative Flashes With Multiple Ground Strike Points Located by the Japanese Lightning Detection Network

Approximately 50% of natural lightning flashes make multiple contacts on the ground. Lightning-induced voltage by nearby lightning stroke is the major cause of overvoltage. The electromagnetic waves emitted by lightning flashes with multiple ground strike points (GSPs) increase new risks to damage electronics information devices located in the vicinity of the GSPs. Therefore, it is very important for electromagnetic compatibility engineering to clarify the characteristics of lightning flashes with multiple GSPs. We have observed lightning discharges over the whole area of Japan detected by the Japanese Lightning Detection Network (JLDN). Specifically, we analyzed negative cloud-to-ground (CG) flashes observed by JLDN within 80 km of Sagamihara in summer. We investigated the median location accuracy of the JLDN in the observation area to evaluate characteristics of spatial distribution of subsequent strokes hitting the GSPs. The median location accuracy varied between 0.2 and 0.4 km in the observed area. The mean multiplicity of negative CG flash observed by JLDN was 3.5. The average inter-stroke interval of new ground contact (NGC) strokes was longer than that of pre-existing channel (PEC) strokes. The ratio of peak current to the first return stroke was higher in the NGC than that in the PECs. Some of flashes hit the ground at several points. The mean number of GSPs was 2.0 per flash, with the mean number of 1.6 subsequent strokes per a GSP. Furthermore, the number of strokes per a GSP has not been previously reported. We also observed that the subsequent strokes altered between different GSPs.

Observation of Natural Lightning-Induced Voltage on Overhead Power Lines

This paper presents the analysis and observation results of the induced voltage waveforms caused by nearby natural lightning on overhead power lines in the Guangzhou field experiment site during the summer of 2008. Peak values of the induced voltage for 36 natural lightning return strokes ranged from 0.21 to 3.87 kV. And the double-peak oscillation phenomenon can be found in the waveforms. The interval time of adjacent return strokes ranged from 17.1 to 430.1 ms. The average 10%-10% peak value duration time of induced voltage waveform of the first return strokes is 244.6 μs, and that of the subsequent return strokes is 83.2 μs. The induced voltage waveforms on the live and neutral conductors are almost the same, while the induced voltage amplitude on the live conductor is slightly larger than that on the neutral conductor. The lightning location system data indicate that the induced voltage on the live and neutral conductor may be of either positive or negative polarity, depending on the lightning ground strike points. However, the amplitude of the induced voltage calculated by the Rusck model is smaller than those of the observation results, with the former being 60% of the latter.

Lightning Induced Disturbances in Buried Cables—Part II: Experiment and Model Validation

This paper presents experimental results obtained at the International Center for Lightning Research and Testing (ICLRT) at Camp Blanding, Florida during the summers of 2002 and 2003. Currents induced by triggered and natural lightning events were measured at the terminations of a buried power cable, in the cable shield, and in the inner cable conductor. Measurements of the horizontal component of the magnetic field above the ground surface for both natural and triggered lightning are also presented. For distant natural lightning events, locations of ground strike points were determined using the U.S. National Lightning Detection Network (NLDN). Based on the theoretical developments presented in Part I of this paper , the field-to-buried cable coupling equations are solved in both the time domain and in the frequency domain. The obtained experimental results are then used to validate the numerical simulations provided by the relevant developed codes.

New insights into lightning processes gained from triggered‐lightning experiments in Florida and Alabama

Analyses of electric and magnetic fields measured at distances from tens to hundreds of meters from the ground strike point of triggered lightning at Camp Blanding, Florida, and at 10 and 20 m at Fort McClellan, Alabama, in conjunction with currents measured at the lightning channel base and with optical observations, allow us to make new inferences on several aspects of the lightning discharge and additionally to verify the recently published “two‐wave” mechanism of the lightning M component. At very close ranges (a few tens of meters or less) the time rate of change of the final portion of the dart leader electric field can be comparable to that of the return stroke. The variation of the close dart leader electric field change with distance is somewhat slower than the inverse proportionality predicted by the uniformly charged leader model, perhaps because of a decrease of leader charge density with decreasing height associated with an incomplete development of the corona sheath at the bottom of the channel. There is a positive linear correlation between the leader electric field change at close range and the succeeding return stroke current peak at the channel base. The formation of each step of a dart‐stepped leader is associated with a charge of a few millicoulombs and a current of a few kiloamperes. In an altitude‐triggered lightning the downward negative leader of the bidirectional leader system and the resulting return stroke serve to provide a relatively low‐impedance connection between the upward moving positive leader tip and the ground, the processes that follow likely being similar to those in classical triggered lightning. Lightning appears to be able to reduce, via breakdown processes in the soil and on the ground surface, the grounding impedance which it initially encounters at the strike point, so at the time of channel‐base current peak the reduced grounding impedance is always much lower than the equivalent impedance of the channel. At close ranges the measured M‐component magnetic fields have waveshapes that are similar to those of the channel‐base currents, whereas the measured M‐component electric fields have waveforms that appear to be the time derivatives of the channel‐base current waveforms, in further confirmation of the “two‐wave” M‐component mechanism.

Ratio of leader to return stroke electric field change for first and subsequent lightning strokes

The ratio of leader to return stroke electric field change versus distance is presented as a function of stroke order for 218 first and subsequent strokes in 70 cloud‐to‐ground flashes which occurred near Tampa, Florida, in 1979. The measured leader to return stroke field ratio tended to be more negative as the stroke order increased, implying that the charge sources for successive strokes were, on average, progressively farther from both the observer and the ground strike point. Sixteen percent of all flashes analyzed contained at least one leader‐return stroke sequence with a negative net electric field change; that is, a ratio that is less than −1. These strokes were observed at distances from 2.5 to 11.6 km, with 56% farther than 8 km. They exhibited a strong tendency to occur late in a flash, with 89% occurring after the fourth stroke. The geometic mean initial electric field peak normalized to 100 km for strokes with a ratio less than −1 was found to be 1.1 V/m, 2.6 times lower than for all subsequent strokes in our data base.

Lightning Induced Voltages on Power Lines: Theory

Theory is presented which shows that nearby lightning return strokes can induce voltage surges of either positive or negative polarity on an overhead line depending on the location of the lightning relative to the line. The Telegraphers' Equations are solved with the return stroke vertical and horizontal electric fields as forcing functions. The hori zontal electric fields are calculated from measured or assumed vertical fields and assuned earth conductivities. For a typical return stroke, voltage waveforms are presented for a line of 500 m length and one of 5 km length for the following conditions: earth conductivities between 10-2 mhos/m and 10-5 mhos/m, earth permittivities between ??= 15 and ??= 3, and lightning ground strike points between 0.2 km and 5.0 km of the line at a variety of positions around the line. Measured voltages on a 460 m test line described in a companion paper are compared with calculated voltage waveforms derived from measured vertical electric fields, in accordance with the developed theory. Calculated waveshapes are found to be in moderately good agreement with the measurements, but calculated magnitudes are about a factor of 4 lower than measured. Possible errors in both theory and measurement are discussed. Voltage measurements reported by other investigators are, in general, consistent with the present theory

Lightning Induced Voltages on Power Lines: Experiment

We present correlated measurements of the voltage induced on a power line by nearby lightning and the vertical electric field intensity from that lightning. Data are given for more than 100 first strokes and more than 200 subsequent strokes with the lightning ground strike point located by triangulation using a network of television cameras and by thunder ranging. Voltages were measured at one end of a 460 m unenergized distribution line which was open-circuited at both ends. A neutral wire was located beneath the line and was grounded at both ends. The time-domain voltaqe and vertical electric field waveforms were detected and recorded on a system having a frequency response from less than 1 Hz to over 1 MHz. Only about half of the vol tage waveforms resemble the classical induced positive surges described in the literature. The magnitude and polarity of the peak induced voltage is a strong function of the location of the lightning ground strike point.