| 1. |
- Abegunawardana, Sidath, et al.
(författare)
-
Audible Frequency Analysis of Ground Flashes
- 2018
-
Konferensbidrag (refereegranskat)abstract
- Thunder signatures categorized into three types based on peak pressure and variation in fundamental frequency, have been studied by using acoustic spectrum of thunder. S-transformation has been used to estimate the dominant frequency variation around the peak pressure. The mean fundamental frequencies of type 3 ground and cloud flashes are 160 Hz and 98 Hz respectively. The mean frequencies of type 2 ground and cloud flashes are 108 Hz and 82 Hz respectively.
|
|
| 2. |
- Abegunawardana, Sidath, et al.
(författare)
-
Sound Source Localization of Lightning Discharges
- 2018
-
Konferensbidrag (refereegranskat)abstract
- The lightning channel can be retraced by thunder signature recorded with an array of microphones. Four microphones were arranged to capture thunder sound, and acoustic cross-correlation of captured pressure signals estimated the time lag of each pair of microphones. A wave segment with 0.25 s or 0.5 s of duration was compared with the acoustic signal recorded by other microphones to estimate time lapse. The direction of channel propagation has been estimated by the time difference of arrival of each pair of microphones. Thunder source locations estimated by this method can be extended to investigate the channel propagation inside clouds.
|
|
| 3. |
- Abewardhana, Ruwan, et al.
(författare)
-
Lightning Localization Based on VHF Broadband Interferometer Developed in Sri Lanka
- 2018
-
Ingår i: 2018 34th international conference on lightning protection (ICLP 2018). - New York : IEEE. - 9781538666357
-
Konferensbidrag (refereegranskat)abstract
- A basic broadband digital interferometer was developed, which is capable of locating Very High Frequency (VHF) radiation sources in two spatial dimensions and time. Three antennas sensed the time series of broadband electromagnetic (EM) signals and digitized with 4 ns sampling interval for a duration of several milliseconds. A technique based on cross-correlations has been implemented for mapping lightning source locations. A map of the first return stroke (RS) and the preceding stepped leader was mapped successfully, using the system with a time resolution of few milliseconds. The result was compared with the visible events of the ground flash to validate the system.
|
|
| 4. |
- Ahmad, Noor Azlinda, et al.
(författare)
-
Characteristics of narrow bipolar pulses observed in Malaysia
- 2010
-
Ingår i: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826 .- 1879-1824. ; 72:5-6, s. 534-540
-
Tidskriftsartikel (refereegranskat)abstract
- Narrow bipolar pulses (NBPs) are considered as isolated intracloud events with higher peak amplitude and strong high frequency emission compared to the first return strokes and other intracloud discharges. From 182 NBPs recorded in Malaysia in the tropic, 75 were narrow negative bipolar pulses (NNBPs) while 107 were narrow positive bipolar pulses (NPBPs). The mean duration of NNBPs was 24.6 +/- 17.1 mu s, while 30.2 +/- 12.3 mu s was observed for NPBPs. The mean full-width at half-maximum (FVVHM) was 2.2 +/- 0.7 and 2.4 +/- 1.4 mu s for NNBPs and NPBPs, respectively. The mean peak amplitude of NPBPs normalized to 100 km was 22.7 V/m, a factor of 1.3 higher than that of NNBPs which is 17.6 V/m. In contrast to the previous studies, it was observed that the electric field change was characterized by a bipolar pulse with a significant amount of fine structures separated by a few tens of nanoseconds intervals, embedded on it. (C) 2010 Elsevier Ltd. All rights reserved.
|
|
| 5. |
|
|
| 6. |
- Ahmad, Noor Azlinda, 1978-, et al.
(författare)
-
Radiation Field Spectra of Long-duration Cloud Flashes
-
Ingår i: IEEE transactions on electromagnetic compatibility (Print). - 0018-9375 .- 1558-187X.
-
Tidskriftsartikel (refereegranskat)abstract
- The radiation electric fields produced by long-duration cloud flashes have been Fourier analyzed to determined the frequency spectrum in the range of 10 kHz to 10 MHz. The flashes were recorded within a distance of less than 20 km. The spectrum was normalized to 50 km distance and it shows a f-1 dependence within the entire frequency range.
|
|
| 7. |
- Ahmad, Noor Azlinda, 1978-, et al.
(författare)
-
Some features of electric field waveform of Narrow Bipolar Pulses
-
Ingår i: Atmospheric research. - 0169-8095 .- 1873-2895.
-
Tidskriftsartikel (refereegranskat)abstract
- Narrow Bipolar Pulses (NBPs) are generated by intra-cloud discharge processes and they are of interest due to their strong broadband and high frequency (HF) emissions. In this study, we present some features of electric field waveform of NBPs which have not been reported in the literature. The HF emission was observed to begin simultaneously with the onset of NBPs indicating no streamers or stepped-leader process was taking place before the initiation of NBPs. The electric field waveforms of NBPs were characterized by many fine peaks embedded intermittently on the rising and decaying edge of NBPs suggesting that some small scale electrical discharges were involved during the formation of NBPs.
|
|
| 8. |
- Ahmad, Noor Azlinda, et al.
(författare)
-
The first electric field pulse of cloud and cloud-to-ground lightning discharges
- 2010
-
Ingår i: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826 .- 1879-1824. ; 72:2-3, s. 143-150
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, the first electric field pulse of cloud and cloud-to-ground discharges were analyzed and compared with other pulses of cloud discharges. Thirty eight cloud discharges and 101 cloud-to-ground discharges have been studied in this analysis. Pulses in cloud discharges were classified as [`]small', [`]medium' and [`]large', depending upon the value of their relative amplitude with respect to that of the average amplitude of the five largest pulses in the flash. We found that parameters, such as pulse duration, rise time, zero crossing time and full-width at half-maximum (FWHMs) of the first pulse of cloud and cloud-to-ground discharges are similar to small pulses that appear in the later stage of cloud discharges. Hence, we suggest that the mechanism of the first pulse of cloud and cloud-to-ground discharges and the mechanism of pulses at the later stage of cloud discharges could be the same.
|
|
| 9. |
|
|
| 10. |
- Baharudin, Zikri A., et al.
(författare)
-
Negative cloud-to-ground lightning flashes in Malaysia
- 2014
-
Ingår i: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826 .- 1879-1824. ; 108, s. 61-67
-
Tidskriftsartikel (refereegranskat)abstract
- The characteristics of the negative cloud-to-ground lightning flashes in Malaysia are studied by analyzing the electric fields generated by the whole flash in nanosecond resolution. A total of 405 strokes obtained from 100 successive negative cloud-to-ground lightning flashes were analyzed, which were recorded from seven convective thunderstorms during the southwest monsoon period, i.e. from April to June 2009. It was found that the total number of interstroke intervals has an arithmetic mean value of 86 ms, a geometric mean value of 67 ms and does not depend on the return stroke order. Of the 100 negative ground flashes, 38 flashes (38%) have at least one subsequent return-stroke (SRS) whose electric field peak was greater than that of the first return-stroke (RS). Furthermore, 58 (19%) out of 305 SRS have electric field peak larger than those of the first RS. The arithmetic and geometric mean ratio between the peak electric field of the SRS and the peak electric field of the first RS are 0.7 and 0.6, respectively. The percentage of single-stroke flashes was 16% while the mean number of strokes per flash and maximum number of stroke per flash were 4 and 14, respectively.
|
|
| 11. |
- Bodhika, J. A. P., et al.
(författare)
-
A preliminary study on characteristics of thunder pulses of lightning
- 2014
-
Ingår i: 2014 INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP). - : IEEE conference proceedings. - 9781479935444 ; , s. 260-264
-
Konferensbidrag (refereegranskat)abstract
- Thunder is the acoustic emission associated with lightning discharges. Thunder signatures have been analyzed by many scientists with the aim of understanding the energy, channel tortuosity and localization of lightning channel. In describing thunder features, a few subjective terms such as clap, roll and rumble have been used in the literature inconsistently with no proper definitions. In this study the features of pressure pulses such as occurrence characteristics and their relative amplitudes were analyzed to understand some of the above mentioned thunder features. Those subjective terms, clap, peal, roll and rumble were quantified along with relative pulse amplitudes and confirmed by listening the recorded thunder signals carefully. The relative peak amplitudes of the pulses of rumble were less than 20% of the peak pulses of the thunder signal and for roll it was between 20% to 40%. Pulses with relative amplitudes greater than 40% were identified as claps. The most significant contribution to the sound in a thunder flash is due to claps, which was studied separately in this study. The number of claps in a thunder flash, their frequency variation, durations, and pulse characteristics has been studied. The frequency of pressure oscillations within these claps are being less than 300 Hz. According to this study, 62% of the flashes consist of 1 to 2 claps. The activity of the thunder signal is high in initial half than the latter half. Thunder signals analyzed in this study is recorded by a microphone system with wide bandwidth range from 6 to 20 kHz.
|
|
| 12. |
- Bodhika, J. A. P., et al.
(författare)
-
Characteristics of thunder pertinent to tropical lightning
- 2018
-
Ingår i: 34th International Conference on Lightning Protection (ICLP) (ICLP 2018). - : IEEE. - 9781538666357
-
Konferensbidrag (refereegranskat)abstract
- Acoustic effects of lightning flashes are not well studied. Thunder also destructive as electric fields do. Thunder flashes of tropical lightning occurred in Hambantota (81(0) 0'E, 6(0) 10'N) close to the southern coast of Sri Lanka were studied. About 90 thunder flashes recorded with the sampling rate of 100 kS/s in 45 s windows were analyzed to identify their characteristics and damaging effects. Results of the analysis on duration of thunder flashes, peak sound pressure levels, occurrence of thunder claps and frequency distribution were presented. The shortest and longest duration of thunder recorded were 2.2 sec and 33.7 sec respectively. About 75% of thunder flashes were remained for about 5-20 sec. The frequency spectrum of a thunder signal could spread up to 1500 Hz. The peak sound pressure level of 30% of recorded thunder flashes at least 3 km away from the lightning were higher than 2 Nm(-2) (100 dB). One to five claps were identified in thunder flashes with 62% having 1 or 2 claps. Sound pressure level, frequency range and its duration are required quantities to estimate the harmful effects of thunder.
|
|
| 13. |
- Bodhika, J. A. P., et al.
(författare)
-
Reconstruction of lightning channel geometry by localizing thunder sources
- 2013
-
Ingår i: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826 .- 1879-1824. ; 102, s. 81-90
-
Tidskriftsartikel (refereegranskat)abstract
- Thunder is generated as a result of a shock wave created by sudden expansion of air in the lightning channel due to high temperature variations. Even though the highest amplitudes of thunder signatures are generated at the return stroke stage, thunder signals generated at other events such as preliminary breakdown pulses also can be of amplitudes which are large enough to record using a sensitive system. In this study, it was attempted to reconstruct the lightning channel geometry of cloud and ground flashes by locating the temporal and spatial variations of thunder sources. Six lightning flashes were reconstructed using the recorded thunder signatures. Possible effects due to atmospheric conditions were neglected. Numerical calculations suggest that the time resolution of the recorded signal and 10 ms(-1)error in speed of sound leads to 2% and 3% errors, respectively, in the calculated coordinates. Reconstructed channel geometries for cloud and ground flashes agreed with the visual observations. Results suggest that the lightning channel can be successfully reconstructed using this technique.
|
|
| 14. |
- Chandimal, Lasantha, et al.
(författare)
-
A field study on the energy dissipation associated with step and touch voltage in earthing systems encased in earth enhancing compounds
- 2024
-
Ingår i: Electric power systems research. - : Elsevier. - 0378-7796 .- 1873-2046. ; 231
-
Tidskriftsartikel (refereegranskat)abstract
- An extensive field experiment was conducted to investigate the effects of earth -enhancing compounds on earthing systems. Four identical vertical earth rods were installed, each encased in concrete, Bentonite, and two commercial enhancing materials. Lightning impulse signals were injected into all electrode arrangements, and the measured responses were used to analyse the associated risks of step and touch voltages. The peak voltage values and the corresponding energy dissipation for each measurement were calculated and compared to those of a reference electrode. The analysis of step voltage measurements and the corresponding energy dissipation demonstrated that the use of concrete exhibited greater advantages than the use of Bentonite. However, touch voltage measurements and the associated energy dissipation indicated that despite the lower touch voltage exhibited by Bentonite, its energy dissipation exceeded that of the reference electrode. Consequently, the unique findings reveal that specific variations of earth -enhancing compounds can exhibit reduced earth impedance and lower step or touch voltages while also yielding higher energy dissipation, introducing an unforeseen risk of injury.
|
|
| 15. |
|
|
| 16. |
|
|
| 17. |
- Cooray, Vernon, et al.
(författare)
-
Lightning parameters of engineering interest
- 2009
-
Ingår i: Lightning Protection. - London : The Institution of Engineering and Technology, London, UK. - 9780863417443
-
Bokkapitel (populärvet., debatt m.m.)
|
|
| 18. |
|
|
| 19. |
- Fernando, Mahendra, et al.
(författare)
-
Lightning and trees
- 2009
-
Ingår i: Lightning Protection. - London : The Institution of Engineering and Technology, London, UK. - 9780863417443
-
Bokkapitel (populärvet., debatt m.m.)
|
|
| 20. |
- Fernando, Mahendra, et al.
(författare)
-
Measurements of lightning-generated electromagnetic fields
- 2012
-
Ingår i: Lightning Electromagnetics. - : IET. - 9781849192156 ; , s. 567-581
-
Bokkapitel (refereegranskat)abstract
- The vertical component of the electric field generated by lightning flashes can be measured either using a field mill or using a flat plate (or a vertical whip) antenna ; each method having its advantages and disadvantages. The three components of the electric field can be measured by using specially adapted spherical antennas.
|
|
| 21. |
|
|
| 22. |
|
|
| 23. |
- Gunasekara, T.A.L.N., et al.
(författare)
-
Time-Frequency Analysis of vertical and horizontal electric field changes of lightning negative return strokes observed in Sri Lanka
- 2018
-
Ingår i: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826 .- 1879-1824. ; 179, s. 34-39
-
Tidskriftsartikel (refereegranskat)abstract
- Simultaneously captured vertical and horizontal (total) electric field signatures of lightning negative Return Strokes (RS) were analyzed to obtain Time-Frequency (TF) variation using Stockwell Transformation (ST). In the study, ST was utilized since it is known to possess comparatively better time resolution at high frequency regions compared to other available TF methods. The data were obtained during the monsoon season of April–May 2014. The vertical and horizontal component of fifty negative RSs was utilized in the study. The resultant ST spectrum was analyzed and the regions of interest were demarcated based on the color which represented their relative power output intensities for different frequency components of the signal. The spread area was identified as the region of frequencies which consisted of power intensity equal or above 90th percentile when compared to the maximum possible value. The spectral area was identified as the area of frequencies in the borderline to the natural background noise. The spread region for the vertical E field had a range between 10 kHz and 650 kHz. Its average values were in between 126 kHz and 331 kHz. The spectral region of the vertical electric field change spanned from 1 kHz to 1020 kHz. Its average distribution was 44 kHz–660 kHz. Horizontal electric fields had a range of 20 kHz–1940 kHz in the spectral region. The same for the spread region was 80 kHz–910 kHz. The averages of the horizontal E field's spectral region were 46–1112 kHz and its spread region varied between 227 and 599 kHz. The results display a higher frequency range for all aspects of the horizontal E field changes which implies that its influence on the high frequency radiation is much higher than its vertical counterpart.
|
|
| 24. |
- Ismail, Mohd Muzafar, et al.
(författare)
-
On the possible origin of chaotic pulse trains in lightning flashes
- 2017
-
Ingår i: Atmosphere. - : MDPI AG. - 2073-4433. ; 8:2
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, electromagnetic field radiation bursts known as chaotic pulse trains (CPTs) and regular pulse trains (RPTs) generated by lightning flashes were analyzed. Through a numerical analysis it was found that a typical CPT could be generated by superimposing several RPTs onto each other. It is suggested that the chaotic pulse trains are created by a superposition of several regular pulse trains. Since regular pulse trains are probably created by dart or dart-stepped leaders or K-changes inside the cloud, chaotic pulse trains are caused by the superposition of electric fields caused by more than one of these leaders or K-changes propagating simultaneously. The hypothesis is supported by the fact that one can find regular pulse trains either in the beginning, middle or later stages of chaotic pulse trains.
|
|
| 25. |
|
|
| 26. |
|
|
| 27. |
|
|
| 28. |
- Nanayakkara, Sankha, et al.
(författare)
-
Features of K-Changes Observed in Sri Lanka in the Tropics
- 2019
-
Ingår i: Atmosphere. - : MDPI AG. - 2073-4433. ; 10:3
-
Tidskriftsartikel (refereegranskat)abstract
- General characteristics of K-changes, including their duration and probability of occurrence associated with ground flashes in Sri Lanka in the tropics, together with their fine structure, are presented. In 98 ground flashes where the small step changes associated with K-changes are clearly visible, there were about two K-changes per flash on average. The mean K-change time duration observed in this study is 0.38 ms. In 53 of the ground flashes, there were 120 consecutive K-changes. In these cases, the geometric mean of the time interval between K-changes was 12 ms. Analysis of the fine structure of the K-changes reveals the K-changes are always associated with either a chaotic pulse train or a combination of chaotic and regular pulse trains. The results suggest that the small step-like static electric fields identified in the literature as K-changes are the step-like static fields associated with the processes that generate chaotic or a combination of chaotic and regular pulse trains. Thus, at larger distances where the static fields are negligible, K-changes may appear as a chaotic pulse train or a combination of chaotic and regular pulse trains.
|
|
| 29. |
- Perera, Chandana, et al.
(författare)
-
Analysis of Channel Tortuosity using 8 m Long Laboratory Sparks
- 2018
-
Ingår i: 34th International Conference on Lightning Protection (ICLP 2018). - : IEEE. - 9781538666357
-
Konferensbidrag (refereegranskat)abstract
- The tortuosity of the channel is defined as "Mean absolute angle change of the angle change and it measures how strongly the tortuous path of the channel of lightning/laboratory spark is twisting. 8 m Long laboratory sparks and high speed (20000 frames per second) technology used for this experiment. Using these data it has been calculated the channel tortuosity of 8 m long sparks and vertical profile of channel tortuosity. In addition to that spectral analysis of the angel change of the twisting path of the channel has been done in this study.
|
|
| 30. |
- Perera, Chandana, et al.
(författare)
-
Continuing Currents and Luminosity of Cloud Flashes
- 2014
-
Ingår i: 2014 INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP). - : IEEE conference proceedings. - 9781479935444 ; , s. 1587-1593
-
Konferensbidrag (refereegranskat)abstract
- In this study, continuing currents and luminosity of cloud flashes were investigated using time resolve photographic technique. In ground flashes, the flow of current after the end of the return stroke is called the continuing currents. Typical cloud flashes have two stages called early stage (or active stage) and final or late stage. The continuing current and luminosities reported in this paper are observed in late stage of the cloud flashes. In ground flashes the shortest reported duration of continuing current is longer than the 3 ms. For the first time in literature the continuing currents in cloud flashes were studied. No major difference between the time duration of continuing currents of ground flashes and long current variation of cloud flashes were observed.
|
|
| 31. |
|
|
| 32. |
|
|
| 33. |
- Sapumanage, Nilantha, et al.
(författare)
-
How physical attributes of transient voltages limit the efficiency of SPD array
- 2018
-
Ingår i: 2018 34th international conference on lightning protection (ICLP 2018). - : IEEE. - 9781538666357
-
Konferensbidrag (refereegranskat)abstract
- This study was conducted to understand what inherent limitations are associated with SPD arrays in confronting with real transient over voltages. To devise the study 403 transient voltages were selected with different physical attributes covering a range of peak-to-peak voltages, starting from 175 V up to 2861 V. The sample comprises 218 cloud-to-clouds and 185 clouds to ground generated transient voltages with mean and median values of 676.80 V and 551.00 V respectively. Impulses were segregated into three subclasses based on their physical attributes and assessed the tendency to drift through the protection array once they placed at the +90, zero and -90 phaser angles. The study revealed that 100% of positive impulses in the sample could drift through the selected array once pitched at any phaser angle on 230 V, 50 Hz utility signal. It was observed that out of the negative pulses, 90.35% at +90, 74.39 % at zero and 42.21% at -90 phaser angles, could freely move through the array. In addition to that, almost 100% of the positive portions of bipolar impulses too can reach the sensitive systems through the protection array irrespective of the pitching phaser angle.
|
|
| 34. |
|
|
| 35. |
|
|
| 36. |
- Sapumanage, Nilantha, et al.
(författare)
-
Insight of SPD limitations caused by incident phaser angle and physical attributes of transient voltages
- 2018
-
Ingår i: 2018 34th international conference on lightning protection (ICLP 2018). - : IEEE. - 9781538666357
-
Konferensbidrag (refereegranskat)abstract
- This study was devised to investigate how the pitching phaser angle and the time domain voltage profile would compel surge protective devices (SPDs) to fall short in providing guaranteed protection. The study showed that the phaser angle at which the transient voltage pitching on the 230 V power frequency signal and its time domain voltage profile play a significant role in deciding the efficiency of the protection array and the amount of incident energy that infiltrates to reach the sensitive loads connected to the low voltage power installation. The analysis managed to prove that the selected SPD array can effectively reduce the harmful energy content of the impulse to around 40% and hence it is always advantageous to have a cascaded array than a single SPD. The study emphasized that it is practically impossible to have a universal protection system that can provide the same degree of protection under all circumstances. Moreover, the study further revealed that it is rational to design a SPD array considering regional and local lightning characteristics.
|
|
| 37. |
|
|
| 38. |
- Sapumanage, Nilantha, et al.
(författare)
-
Simulation of the surge performance of the external lightning protection system
- 2018
-
Ingår i: 2018 34th international conference on lightning protection (ICLP 2018). - : IEEE. - 9781538666357
-
Konferensbidrag (refereegranskat)abstract
- This paper presents an analysis done on the transient behavior of an external lightning protection system (LPS). The study was devised by modeling a Faraday's cage type LPS of a five-storied building on a MATLAB based electrical nodal network and simulating it against the 10/350 mu s lightning impulse with a peak current of 30 kA. The study focused on the down conductor material cross section area, ground impedance and the number of down conductors in the LPS to establish which factor or factors have more influence on the LPS performance. The simulation concludes that under the transient conditions the voltage dissipation on the LPS can reach several thousand volts and the peak branch current disbursements in the network are in the order of 2-2.5 kA. However, under poor ground conditions and less number of down conductors, voltage rise on the LPS system can elevate alarmingly, and branch currents tend to increase close to 7.5 kA. The study proved that the performance of the LPS and the magnitudes of the negative consequences of the associated secondary effects such as electromagnetic compatibility issues and risk associated with high step voltage issues, etc., have a close correlation with the ground impedance and the number of down conductors than that of the cross-section area of the down conductors.
|
|
| 39. |
- Sapumanage, Nilantha, et al.
(författare)
-
Study on responses of SPDs against the transient voltages generated by CG flashes
- 2018
-
Konferensbidrag (refereegranskat)abstract
- This study presents the behavior of surge protecting devices (SPDs) against transient over voltages generated by cloud to ground (CG) flashes. Analysis revealed that lightning generated transient over voltages have a potential to impart detrimental effects on the SPDs. Moreover, it was concluded that comparisons between IEC laboratory impulse and the real transient voltages are remote due to factors such as peculiar time domain voltage profiles, random polarities, multiple surges with very narrow inter pulse durations in the order of microseconds. Further, observed that SPDs would not always retain within the limits specified by the manufactures under all circumstances.
|
|
| 40. |
- Sapumanage, Nilantha, et al.
(författare)
-
Time-Frequency and Energy Correlations of the Transient Voltages Triggered by Cloud to Cloud Discharges
- 2019
-
Ingår i: IEEE transactions on electromagnetic compatibility (Print). - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9375 .- 1558-187X. ; 61:6, s. 1782-1792
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a study performed on time, frequency, and energy correlations of transient voltages generated by the cloud to cloud discharges. It revealed that the energy embedded in transient voltages have been lumped over few segments of time domain voltage profile than uniquely scattering over the time span. The study further determined that the energy concentration becomes higher in and around the vicinity of the time domain voltage maxima or minima, and such high energy-concentrated segments confined to a minute time span in comparison to the total time span of the transient voltage. The study also established that there is a small time lead or lag between the time domain voltage maxima or minima and the time of energy maximize. Moreover, the analysis deduced that the time lead or time lag phenomenon, is not sensitive to the orientation of the time domain voltage profile, but fuelled by the pulse type. The response time of surge protective devices can become crucial if the stipulated clamping voltages of the protection devices fall close to local peaks of the transient voltages.
|
|
| 41. |
|
|
| 42. |
- Sharma, S. R., et al.
(författare)
-
Isolated breakdown activity in Swedish lightning
- 2008
-
Ingår i: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826 .- 1879-1824. ; 70:8-9, s. 1213-1221
-
Tidskriftsartikel (refereegranskat)abstract
- The initial breakdown processes or preliminary breakdown (PB) processes are generally associated with either cloud or cloud-ground lightning flashes, and hence have been studied mainly in connection with those subsequent activities. However, it has been observed in the summer thunderstorms of Sweden that there are breakdown processes that may not culminate into any subsequent activity. As these processes do not lead to any subsequent activity, they have been termed as isolated breakdown activities. Such isolated breakdown activities involve microsecond-scale pulses with both initial polarities. Based on their polarities, breakdown processes are divided into two groups, the negative breakdown pulses that are similar to the breakdown pulses leading to negative return strokes in ground flashes and the positive breakdown pulses similar to the breakdown pulses generally leading to the cloud flashes. The occurrence of the two types of breakdown processes is found to vary from a thunderstorm day to the other. In the present study, the signatures of isolated breakdown activities have been analyzed and are compared with those leading to the subsequent activities observed during the same measurement campaign. The average duration of the isolated breakdown activity associated with the negative initial polarity pulses is found to be 0.98 ms with average number of pulses 8.5. Similarly, the average duration and number of pulses in the isolated breakdown process with positive initial polarity pulses are 6.9ms and 3.9, respectively.
|
|
| 43. |
- Sharma, S. R., et al.
(författare)
-
Narrow positive bipolar radiation from lightning observed in Sri Lanka
- 2008
-
Ingår i: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826. ; 70:10, s. 1251-1260
-
Tidskriftsartikel (refereegranskat)abstract
- Narrow positive bipolar pulses (NPBPs), whose origin largely remains unknown as yet, have occasionally been noticed in Sri Lanka. These discharges are found to be opposite in polarity to that of negative return strokes, and are found to occur at the beginning and active stage of thunderstorm activities in Sri Lanka. They are emitted from the thunderstorms that produce other activities also and are relatively narrower, bipolar and isolated in nature. They are neither preceded by leader-type pulses nor succeeded by the subsequent activities and hence, could not be associated with any other known activity. Similar radiations have previously been identified and termed as NPBPs. Their features are indeed unique and different from the other known thunderstorm electrical processes. These events have been found to be accompanied by the HF radiations at 5 and 10 MHz, at the trailing part of the pulse. However, such narrow, bipolar and isolated events have not been observed in Sweden, during a lightning measurement campaign at Uppsala, in 2006. So, it is speculated that the meteorological conditions to be responsible for the thunderstorm activity to produce such pulses. Features of such pulses recorded on different thunderstorm days in 2005 and 2006 have been analyzed and presented in this study. The average rise time (10-90%) (Tr), of the pulses was found to be 2.6 [mu]s, the average zero crossing time (Tz) was found to be 5.85 [mu]s, the average duration of slow front (Ts) was found to be 1.86 [mu]s, and the average ratio of amplitude of overshoot to the corresponding peak amplitude (Os/Pa) of these pulses was found to be 0.39.
|
|
| 44. |
- Sharma, S R, et al.
(författare)
-
Temporal features of different lightning events revealed from wavelet transform
- 2011
-
Ingår i: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826 .- 1879-1824. ; 73:4, s. 507-515
-
Tidskriftsartikel (refereegranskat)abstract
- Various lightning events are analysed using wavelet transform. The events include PB pulses, stepped leaders, first return strokes, subsequent strokes associated with negative ground flashes, positive return strokes and narrow bipolar pulses. Time domain electric fields were recorded from tropical and temperate thunderstorms. PB pulses pertinent to the tropical thunderstorms are found to radiate in the average frequency range 51-739 kHz. Leaders are found to radiate in the frequency range 87-720 kHz. The energy radiated by the negative return strokes is predominant in the range 2.8-40 kHz. The energy radiated by the first subsequent strokes predominantly lies in the frequency range 4.5-55 kHz. Positive return strokes are found to radiate predominantly in the frequency range 5.5-81 kHz. Narrow bipolar pulses are found to predominantly radiate in the frequency range 58-714 kHz.
|
|
| 45. |
- Sharma, S R, et al.
(författare)
-
Unique lightning activities pertinent to tropical and temperate thunderstorms
- 2011
-
Ingår i: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826 .- 1879-1824. ; 73:4, s. 483-487
-
Tidskriftsartikel (refereegranskat)abstract
- Observations from two geographical locations show that some lightning events are unique and specific to the respective thunderstorms. From the measurements conducted in a tropical country, Sri Lanka, and a temperate country, Sweden, it is observed that there are some lightning activities that are unique for each location. Narrow bipolar pulses (NBPs) have frequently been observed in the tropical thunderstorms and were not observed in the temperate thunderstorms, whereas isolated breakdown pulses (IBPs) have frequently been observed in the temperate thunderstorms and were not observed in the tropical thunderstorms. It can be speculated that NBPs are the unique features of tropical thunderstorms and that IBPs are the unique features pertinent to the temperate thunderstorms.
|
|
| 46. |
|
|
| 47. |
|
|
| 48. |
|
|
| 49. |
|
|
| 50. |
- Vayanganie, S.P.A, et al.
(författare)
-
High Speed Optical Observations of Cloud Flashes
- 2014
-
Ingår i: 2014 INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP). - : IEEE conference proceedings. - 9781479935444 ; , s. 752-755
-
Konferensbidrag (refereegranskat)abstract
- Luminosity variations of natural cloud lightning channels were studied using high speed video recordings in Sri Lanka in the tropic. Five cloud flashes were selected for the study, which were recorded with 5000 fps with 512X512 pixel resolution. Luminosity variation along channels and along selected channel segment, duration of cloud activities was studied. It was found that the average duration of selected flashes is 266.44 ms. No particular pattern was observed for the luminosity variation along channel segments. However the luminosity variation across the channel followed a Gaussian distribution pattern. Pattern of the luminosity variation along channels were compared with existing models to understand the development process of cloud flashes. Results show that it is hard to collaborate the observation to a single process for cloud discharges.
|
|
