Negative Lightning Flashes Research Articles

Polarity Asymmetries in Rocket‐Triggered Lightning

AbstractThe dissonant development of positive and negative lightning leaders is a central question in atmospheric electricity. It is also the likely root cause of other reported asymmetries between positive and negative lightning flashes, including the ones regarding: stroke multiplicity, recoil activity, leader velocities, and emission of energetic radiation. In an effort to contrast lightning leaders of different polarities, we highlight the staggering differences between two rocket‐triggered lightning flashes. The flash beginning with upward positive leaders exhibits an initial continuous current stage followed by multiple sequences of dart leaders and return strokes. On the other, in its opposite‐polarity counterpart, the upward development of negative leaders is by itself the entire flash. As a result, the flash with negative leaders is faster, briefer, transfers less charge to the ground, has lower currents, and smaller spatial extent. We conclude by presenting a discussion on the three fundamental leader propagation modes.

Differences in the response of transmission lines subjected to the currents of negative and positive lightning flashes: Influence of ground terminations

The differences on the lightning response of transmission lines, whose towers are subjected to the impression of pulses of current of first negative return strokes and of positive flashes, are determined by computational simulation. It is shown that the amplitude of the resulting transient overvoltages across insulators per unit of impressed current is much larger for negative return strokes. As most of the traditional procedures for assessing lightning performance of transmission lines ignore these differences, their results can exhibit significant errors.

On the processes leading to different modes of charge transfer in negative flashes according to fast videos and correlated records of current and electric field

This work discusses the processes involved in different modes of charge transfer in negative lightning flashes, taking as reference video-records obtained with a fast camera and records of current and close electric-field measured at Morro do Cachimbo Station. The data of two downward and one upward negative flashes are explored for considering the features of these processes and for supporting their interpretation, based on the bidirectional and bipolar leader approach. The processes comprise three sequences (stepped leader - first return stroke, dart leader - subsequent return stroke, dart-stepped leader - subsequent return stroke), in addition to the initial continuous current in upward lightning, return strokes following it, continuing current and M-components, the latter observed superimposed on both the continuing current and the tail of return stroke currents. An unreported process of charge transfer, consisting of the reignition of the dissipating leader of an upward lightning from the ground to the cloud is analyzed as well.

Upward Bipolar Lightning Flashes Originated From the Connection of Recoil Leaders With Intracloud Lightning

AbstractThe present work shows high‐speed videos of two upward flashes that started with positive upward leaders and, instead of being followed by negative subsequent return strokes, they were followed by positive subsequent return strokes. In both cases, after the positive leaders developed, recoil leaders (RL) appeared in their decayed branches as would be usual in negative upward lightning flashes. However, in these flashes the negative end of a recoil leader connected to a positive leader of an intracloud (IC) flash nearby. The connection initiated a downward positive leader that re‐ionized the decayed channel of the upward flash all the way to the tower giving origin to a positive subsequent return stroke. This work shows that RL do play an important role in the occurrence of bipolar upward flashes and their interaction with IC flashes can provide explanations for all types of bipolar upward flashes initiated by upward positive leaders.

Bidirectional Recoil Leaders in Upward Lightning Flashes Observed at the Säntis Tower

AbstractWe report the observation of three negative upward flashes recorded by a high‐speed camera at the Säntis Tower during the Summer of 2019. The camera was operating at 10,000 fps and an exposure time of 99 μs. Simultaneous measurements of the lightning current were obtained for all three flashes. The close electric field was measured for one of the observed flashes, which was analyzed in detail. In this flash, we observed 50 recoil leaders developing in the decayed channel with speeds characteristic of dart leader processes. Out of the 50 recoil leaders, 45 ended up as attempted leaders, three developed into M‐component‐type ICC (initial continuous current) processes, and two into return strokes. This study reveals that depending on the spatial and temporal properties of electric field in the area of the event and the main channel condition, recoil leaders can develop into different processes in upward negative lightning flashes such as attempted leaders, M‐components, M‐component‐type ICC events, mixed mode pulses, or return strokes. We observed M‐component‐type ICC events with junction heights as low as 137 m, while all of the observed mixed mode pulses seemed to attach directly to the structure. Bidirectional propagation of the recoil leader was also observed.

Latitude and Topographical Dependence of Lightning Return Stroke Peak Current in Natural and Tower-Initiated Negative Ground Flashes

Experimental data show that the peak currents of first and subsequent lightning return strokes in negative ground flashes increase with decreasing latitude. In this paper, the reason for this dependence of peak return stroke current on latitude is explained using the fact that the height of the charge centers increases with decreasing latitude. Results show that in tropical regions where the height to the negative charge center is about 8 km, the median values of the first and the subsequent return stroke peak currents are about 42 kA and 15 kA, respectively. If the height to the charge center is larger than 8 km, the peak currents will also become larger. For example, if the location of the charge center is increased to about 9 km, the median values of the first and subsequent return stroke peak currents will increase to about 45 kA and 16 kA respectively. The same reasoning shows that, even in the same geographical region, the peak return stroke current may decrease as the elevation of the ground where the lightning strikes take place increases. The results also indicate that the peak subsequent return stroke current in tower-initiated negative lightning flashes decreases as the height of the tower increases. These theoretical predictions are in general agreement with the available experimental data.

Comparisons of optical characteristics of two upward lightning flashes triggered by a nearby positive cloud-to-ground lightning

The propagation characteristics of two upward negative lightning flashes, which were initiated from the tops of two tall grounded structures immediately after the return stroke (RS) initiation of one nearby positive cloud-to-ground (CG) lightning flash, have been investigated and compared based on high-speed video observations. Two upward flashes show significant difference in their propagation characteristics mainly due to the existence of lower cloud layer near the Canton tower. Upward flash initiated from the top of Canton tower produces several large luminous pulses, with the enhanced luminosity mostly concentrating near the lower cloud, and it propagates faster beyond the lower cloud, while the brightness of the other upward flash does not vary much and distributes almost uniformly along the discharge channel. The major reason for these differences might lie in the instantaneous negative charge neutralization inside the lower cloud with the positive charges along the discharge channel, when the positive leader propagates upward across the lower cloud layer. After about 90 ms the upward flash initiated from the tall building produces a dart-leader subsequent RS, but it extinguishes faster than the other one.

Progression Features of Dart Leaders in Natural Negative Cloud‐to‐Ground Lightning Flashes

AbstractWe have analyzed the propagation process of nine dart leaders in four natural negative lightning flashes observed by a high speed optical system LAPOS 5. The propagation speeds range from 0.6 to 3.7×107 m/s with an average value of 1.5×107 m/s. The leader luminosity peaks at the front part of the leader head and decreases gradually backward within the head. The leader channel behind the leader head has a relatively low and constant luminosity. The average luminosity of the leader head is about 1.3 times brighter than that of the leader channel behind. The head lengths of seven dart leaders were estimated to range from 21 to 88 m. Our results show that as the ground is approached, the dart leader propagates faster with its leader head growing brighter and longer. For different strokes within an individual lightning flash, it was found that the larger change ratio of leader head brightness relates with the larger change ratio of propagation speed and the larger change ratio of leader head length.

Investigation of Overvoltages in HV Underground Sections Caused by Direct Strokes Considering the Frequency-Dependent Characteristics of Grounding

Nowadays, the analysis of the lightning performance of high-voltage (HV) underground sections has become increasingly important, thanks to their increasing usage with overhead transmission lines. In this way, the objective of this paper is to investigate the sensitivity of the overvoltages, at the terminal of underground cables (UCs), due to the incidence of negative lightning flashes at the shield wire or the tower top. It is done by means of different representations of the grounding behavior, different points of lightning incidence, different values of soil resistivity, and considering or not the variation of the soil electrical parameters with frequency. It is observed that a reliable investigation on lightning overvoltages is important and it must consider a suitable representation of the grounding behavior. An improper modeling can lead to nonrepresentative results. In this way, it is highlighted how the frequency dependence of the soil parameters influences the results in many different situations. For long distances from the UCs and low soil resistivity regions, all the grounding models produce similar results. On the other hand, for regions with high soil resistivities, the use of a proper model for the tower grounding is important, since the discrepancies between the results produced considering or not the dependence of the soil parameters with frequency become substantial. The inclusion of the grounding behavior with frequency allows to obtain reliable simulations of the transient behavior of the insulated cables, which constitute the underground section under study.

Sub Microsecond Analysis of Negative Cloud-To-Ground Lightning Flashes

This paper expounds a development software for the identification of lightning discharge in cloud-to-ground flashes. The study was to reduce a misleading detection of the electric field radiation of a lightning discharge profile by considering the important parameters of sub microseconds structure of lightning return stroke. The software was built-in MATLAB. The development of the software considered the important parameter of return strokes such as peak value, zero crossing, rising time and fast transition time. We used a modelling technique for training and patterning the 19 return stroke from electric radiation field generated by the negative cloud-ground lightning flashes recorded in Universiti Teknikal Malaysia Melaka. The 19 return strokes data were recorded by using Lecroy HDO4024 with 5 MS/s. The results showed that the software had the ability to recognize the lightning parameters such as peak value, zero crossing, rising time and fast transition time. In conclusion, the software was able solved the uncertainty of the unknown cloud-to-ground lightning flashes parameter. This paper expounds a programmed development software for the used to do identification of the characteristi cs o o f the lightning d is charge either in cloud -to - and ground flashes cloud and ground flashes of the lightning strikes . Th e study was to reduc e e a m is leadi ng detection of the electric field radiation of a lightning d is charge profile by considering the important pa ra meters o f sub microseconds structure of lightning return stroke . programmed should resolved the problem of unidentified signal o f lightning strikes. The softw are was built-in MATLAB . The development of the softw are considered the important parameter of return stroke s such as peak value, software to recognize t he pattern of the lightning strikes of cloud-to-gr ound flashes or cloud-to-cloud flashes by determining the multiple parameters suc h as zero crossing, rising time and fast transition time. MAKLUMKAN KAEDAH YG “MUNGKIN” MELIBATKAN TRAIN BEBERAPA DATA CTH — We used a modelling technique A for training and patterning the 19 return stroke from electric radiation field generated by the negative cloud - ground lightning flashes recorded in Universiti Teknikal Malaysia Melaka . The 19 return strokes data were recorded by using Lec r oy HDO4024 with 5 MS/s. First, the lightning pattern is described, then the programmed was tested to recognize all the parameters to identify the types of the lightning strikes. The results show ed s th at the e software had the ability to recognize the lightning parameters such as peak value, zero crossing, rising time and fast transition time. In conclusion, t he softw are was able solve d the uncertainty of the unknown cloud - to - ground unknown lightning flas hes parameter. At last, some suggestions are given to improve the system for future research. Masukan Brief of conclusion…. Normal 0 false false false MS X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:Table Normal; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:Times New Roman,serif; mso-ansi-language:MS; mso-fareast-language:MS;}

Length estimations of presumed upward connecting leaders in lightning flashes to flat water and flat ground

Using video data recorded at 50,000 frames per second for nearby negative lightning flashes, estimates are derived for the length of positive upward connecting leaders (UCLs) that presumably formed prior to new ground attachments. Return strokes were 1.7 to 7.8 km distant, yielding image resolutions of 4.25 to 19.5 m. No UCLs are imaged in these data, indicating those features were too transient or too dim compared to other lightning processes that are imaged at these resolutions. Upper bound lengths for 17 presumed UCLs are determined from the height above flat ground or water of the successful stepped leader tip in the image immediately prior to (within 20 μs before) the return stroke. Better estimates of maximum UCL lengths are determined using the downward stepped leader tip's speed of advance and the estimated return stroke time within its first frame. For 17 strokes, the upper bound length of the possible UCL averages 31.6 m and ranges from 11.3 to 50.3 m. Among the close strokes (those with spatial resolution <8 m per pixel), the five which connected to water (salt water lagoon) have UCL upper bound estimates averaging significantly shorter (24.1 m) than the average for the three close strokes which connected to land (36.9 m). The better estimates of maximum UCL lengths for the eight close strokes average 20.2 m, with slightly shorter average of 18.3 m for the five that connected to water. All the better estimates of UCL maximum lengths are <38 m in this dataset

An Analysis of Current and Electric Field Pulses Associated With Upward Negative Lightning Flashes Initiated from the Säntis Tower

AbstractWe present a study on the characteristics of current and electric field pulses associated with upward lightning flashes initiated from the instrumented Säntis Tower in Switzerland. The electric field was measured 15 km from the tower. Upward flashes always begin with the initial stage composed of the upward‐leader phase and the initial‐continuous‐current (ICC) phase. Four types of current pulses are identified and analyzed in the paper: (1) return‐stroke pulses, which occur after the extinction of the ICC and are preceded by essentially no‐current time intervals; (2) mixed‐mode ICC pulses, defined as fast pulses superimposed on the ICC, which have characteristics very similar to those of return strokes and are believed to be associated with the reactivation of a decayed branch or the connection of a newly created channel to the ICC‐carrying channel at relatively small junction heights; (3) “classical” M‐component pulses superimposed on the continuing current following some return strokes; and (4) M‐component‐type ICC pulses, presumably associated with the reactivation of a decayed branch or the connection of a newly created channel to the ICC‐carrying channel at relatively large junction heights. We consider a data set consisting of 9 return‐stroke pulses, 70 mixed‐mode ICC pulses, 11 classical M‐component pulses, and 19 M‐component‐type ICC pulses (a total of 109 pulses). The salient characteristics of the current and field waveforms are analyzed. A new criterion is proposed to distinguish between mixed‐mode and M‐component‐type pulses, which is based on the current waveform features. The characteristics of M‐component‐type pulses during the initial stage are found to be similar to those of classical M‐component pulses occurring during the continuing current after some return strokes. It is also found that about 41% of mixed‐mode ICC pulses were preceded by microsecond‐scale pulses occurring in electric field records some hundreds of microseconds prior to the onset of the current, very similar to microsecond‐scale electric field pulses observed for M‐component‐type ICC pulses and which can be attributed to the junction of an in‐cloud leader channel to the current‐carrying channel to ground. Classical M‐component pulses and M‐component‐type ICC pulses tend to have larger risetimes ranging from 6.3 to 430 μs. On the other hand, return‐stroke pulses and mixed‐mode ICC pulses have current risetimes ranging from 0.5 to 28 μs. Finally, our data suggest that the 8‐μs criterion for the current risetime proposed by Flache et al. is a reasonable tool to distinguish between return strokes and classical M‐components. However, mixed‐mode ICC pulses superimposed on the ICC can sometimes have considerably longer risetimes, up to about 28 μs, as observed in this study.

Some Return Stroke Characteristics of Negative Lightning Flashes Recorded at the Peissenberg Tower

Subject matter of the paper is the analysis of the return stroke characteristics of negative lightning flashes recorded with the Peissenberg Measuring Station, Germany. Four negative first return strokes were measured. All of them were single-stroke lightning having a first stroke, but no subsequent stroke. The arithmetic mean value is 42.8 kA for the peak current, 7.4 μs for the 10% to 90% current risetime, 13.5 C for the charge, 182·103 A2s for the specific energy (action integral), and 15.5 kA/μs for the maximum current steepness. The associated electric fields exhibited a field change of opposite polarity prior to the initiation of the return stroke current. The same waveform was found for the electric field of other triggered negative upward lightning, except of the different time scale. The currents of the total of 105 negative subsequent return strokes were also recorded, 68 of them with the measurement equipment were used up to the year 1999, and 37 of them with the new measurement equipment were used since 2008. Based on the measurements up to 1999, the arithmetic mean values of the current peak and of the maximum current derivative are 9 kA and 45 kA/μs, respectively. For the measurements since 2008, the arithmetic mean value of the current peak is 10.1 kA.

Upward lightning flashes characteristics from high‐speed videos

AbstractOne hundred high‐speed video recordings (72 cases in Brazil and 28 cases in USA) of negative upward lightning flashes were analyzed. All upward flashes were triggered by another discharge, most of them positive CG flashes. A negative leader passing over the tower(s) was frequently seen in the high‐speed video recordings before the initiation of the upward leader. One triggering component can sometimes initiate upward leader in several towers. Characteristics of leader branching, ICC pulses, recoil leader incidence, and interpulse interval are presented in this work. A comparison of the results is done for data obtained in Brazil and USA. The duration of ICC and the total flash duration are on average longer in Brazil than in USA. Only one fourth of all upward leaders are followed by any return strokes both in Brazil and USA, and the average number of return strokes following each upward leader is very low. The presence and duration of CC following return strokes in Brazil is more than two times larger than in USA. Several parameters of upward flashes were compared with similar ones from cloud‐to‐ground flashes.

Statistical analysis of electric field parameters for negative lightning in Malaysia

This paper presents a comparative study on the electric field and its derivative parameters of negative lightning in Malaysia and other regions. This study is the first in Malaysia where the parameters of negative electric field and its derivative are thoroughly analyzed. 104 negative lightning flashes containing 277 negative return strokes occurring within 10–100km from the measuring station and recorded during monsoon period in the state of Johor, Malaysia had been analyzed. It was found that 73% of the recorded flashes are multiple strokes with an average multiplicity of 2.6 strokes per flash. For first return strokes, the arithmetic mean (AM) of initial peak electric field and the AM of initial peak electric field derivative are 21.8V/m and 11.3V/m/µs, respectively. The initial peaks of electric field and its derivative for first return strokes are larger than those for the subsequent return strokes. Comparison of overall results with those obtained earlier in Sri Lanka, Germany, Sweden, Japan, Florida indicates that several electric field and its derivative parameters are affected by propagation media and geographical region. Similarity of results with other countries having the same climatic condition is also observed.

Two basic leader connection scenarios observed in negative lightning attachment process

High-speed video images of 24 downward negative lightning flashes terminating on tall structures in Guangzhou are selected to analyse the connecting behaviour of the downward and upward leaders during the attachment process preceding the first return stroke. Three types of leader connecting behaviour have been observed: Type I, the tip of downward leader (DL) to the tip of upward connecting leader (UCL), which accounts for 42% of all the events (10/24); Type II, the DL's tip to the lateral surface of UCL, which accounts for 50% (12/24); and Type III, the combination of Types I and II, which accounts for 8% (2/24). For the two cases of Type III behaviour, each case had two junction points (one with Type I and the other with Type II behaviour) between the downward and upward leaders. Therefore, Types I and II can be viewed as the two basic types of the leader connecting behaviour during the attachment process in negative lightning. No attachment process exhibited the connection of the UCL's tip to the lateral surface of DL. The presence of multiple DL branches and their integrated effect on the development of positive UCL/UCLs are likely to be the main reasons for the Type II behaviour.

On Lightning Electromagnetic Field Propagation Along an Irregular Terrain

In this paper, we present a theoretical analysis of the propagation effects of lightning electromagnetic fields over a mountainous terrain. The analysis is supported by experimental observations consisting of simultaneous records of lightning currents and electric fields associated with upward negative lightning flashes to the instrumented Santis tower in Switzerland. The propagation of lightning electromagnetic fields along the mountainous region around the Santis tower is simulated using a full-wave approach based on the finite-difference time-domain method and using the two-dimensional topographic map along the direct path between the tower and the field measurement station located at about 15 km from the tower. We show that, considering the real irregular terrain between the Santis tower and the field measurement station, both the waveshape and amplitude of the simulated electric fields associated with return strokes and fast initial continuous current pulses are in excellent agreement with the measured waveforms. On the other hand, the assumption of a flat ground results in a significant underestimation of the peak electric field. Finally, we discuss the sensitivity of the obtained results to the assumed values for the return stroke speed and the ground conductivity, the adopted return stroke model, as well as the presence of the building on which the sensors were located.

Attachment process in subsequent strokes and residual channel luminosity between strokes of natural lightning

AbstractWe examined high‐speed video and electric field records of 23 subsequent strokes following the previous stroke channel in three natural negative lightning flashes, which were obtained at the Lightning Observatory in Gainesville (LOG), Florida. Five strokes exhibited faintly luminous formations (FLFs) occurring in a single, pre‐return‐stroke frame and ranging from 130 to 908 m in length between the lower end of downward leader and the prospective strike point. The FLFs were inferred to be not streamers (as in first strokes) but manifestations of an increase in conduction current in the defunct channel between the leader and ground in response to the increasing electric field produced by the descending leader. Further, in eight strokes, we observed residual channel luminosity persisting over many frames (for 4.7 to 18 ms), through the pre‐return‐stroke frame. The residual luminosity was apparently associated with a stronger channel heating and a larger channel radius (and hence a lower temperature decay rate), both associated with the relatively long preceding continuing current. Presence of either FLF or residual channel luminosity did not appear to significantly influence the mode and velocity of propagation of the descending leader.

When does the lightning attachment process actually begin?

AbstractHigh‐speed video and electric field records of 43 first and 7 new‐ground‐termination subsequent strokes in negative lightning flashes, obtained at the Lightning Observatory in Gainesville, Florida, were examined. Eighteen (36%) of these strokes exhibited faintly luminous formations (FLFs) below the downward leader tip just prior to the return stroke. All the 18 FLFs were connected to the strike object on the ground, with 14 of them being also in contact with the downward leader tip. For 11 located events showing FLFs in contact with the downward leader tip, the FLF 2‐D length ranged from 51 to 200 m and the time interval between the end of exposure of the FLF frame and the return stroke onset ranged from 42 to 106 μs. We inferred that the FLFs mostly consisted of relatively low conductivity streamers, based on the following observations and estimates. (a) The rates at which the 11 FLFs were replaced by channels capable of guiding return stroke waves ranged from 0.7 × 106 m/s to 2.2 × 106 m/s, which is comparable to leader speeds in virgin air (in the same records). (b) The overwhelming majority of downward leaders continued stepping while being connected to ground via FLFs. (c) The average electric field along FLFs is 1 to 2 orders of magnitude higher than expected for hot, leader‐like channels. Since in all cases the FLF determined the strike point, we conclude that its inferred initiation up to a few hundreds of microseconds before the return stroke onset signified the beginning of the lightning attachment process.

Influence of Configuration of Line Installed Together on Sparkover Rate of Medium-Voltage Line

An electric line having lower insulation voltage is often installed together with a medium-voltage distribution line and in the case of direct strokes to an OHGW (overhead ground wire), the sparkover of such a line occurs prior to that of a medium-voltage line. In this paper, the authors picked up a low-voltage distribution line as a representative of such a line and investigate the influence of the configuration of a low-voltage line on the sparkover rate of a medium-voltage line associated with direct negative lightning flashes based on the numerical calculation of the insulator voltage by the EMTP. The low-voltage line grounded by the sparkover plays a role similar to the OHGW installed below a medium-voltage line and it turns out that the line installed together with a medium-voltage, represented by a low-voltage line in this paper, greatly influences the sparkover rate of a medium-voltage line.