| 1. |
- Cooray, Gerald, et al.
(author)
-
Application of electromagnetic fields of an accelerating charge to obtain the electromagnetic fields of a propagating current pulse
- 2012
-
In: Lightning Electromagnetics. - : IET. - 9781849192156 ; , s. 55-65
-
Book chapter (peer-reviewed)abstract
- It was recently demonstrated that electromagnetic fields from accelerating charges can be utilized to evaluate the electromagnetic fields from lightning return strokes. It was documented in detail how to utilize the equations to calculate electromagnetic fields of various engineering return stroke models, both current propagation and current generation types.It was also demonstrated how the equations can be utilized to calculate radiation fields generated by currents propagating along transmission lines in the presence of bends. The basics of this technique are summarized in this chapter by applying it to evaluate the electromagnetic fields of a propagating current pulse.
|
|
| 2. |
- Cooray, Gerald, et al.
(author)
-
Electromagnetic fields of a short electric dipole in free space - revisited
- 2012
-
In: PROG ELECTROMAGN RES. - 1559-8985. ; 131, s. 357-373
-
Journal article (peer-reviewed)abstract
- Maxwell's equations specify that electromagnetic radiation fields are generated by accelerating charges. However, the electromagnetic radiation fields of an accelerating charge are seldom used to derive the electromagnetic fields of radiating systems. In this paper, the equations pertinent to the electromagnetic fields generated by accelerating charges are utilized to evaluate the electromagnetic fields of a current path of length l for the case when a pulse of current propagates with constant velocity. According to these equations, radiation is generated only at the end points of the channel where charges are being accelerated or decelerated. The electromagnetic fields of a short dipole are extracted from these equations when r >> l, where r is the distance to the point of observation. The speed of propagation of the pulse enters into the electromagnetic fields only in the terms that are second order in l and they can be neglected in the dipole approximation. The results illustrate how the radiation fields emanating from the two ends of the dipole give rise to field terms varying as 1/r and 1/r(2), while the time-variant stationary charges at the ends of the dipole contribute to field terms varying as 1/r(2) and 1/r(3).
|
|
| 3. |
|
|
| 4. |
- Cooray, Vernon, et al.
(author)
-
Basic electromagnetic theory - a summary
- 2012
-
In: Lightning Electromagnetics. - : The Institution of Engineering and Technology. - 9781849192156
-
Book chapter (peer-reviewed)abstract
- The goal of this chapter is to provide a summary of the basic concepts of electro- magnetic theory as a complement to the subject matter, most of which is related to electromagnetism, discussed in this book. The chapter covers only the concepts that are necessary to understand the electromagnetics of lightning flashes.
|
|
| 5. |
- Cooray, Vernon, et al.
(author)
-
Corona currents generated from a person’s head in the vicinity of lightning strikes : Stimulation ofphosphenes
- 2011
-
In: 7th Asia-Pacific International Conference on Lightning.
-
Conference paper (peer-reviewed)abstract
- Phosphene is a sensory experience which occurs dueto the interaction of electric currents generated by an externalagent with the visual cortex or retina. Occurrence of phospheneshas been documented in clinical Transcranial MagneticStimulation (TMS) studies where electric fields are induced inthe brain by the application of time varying magnetic fields. Inthis paper the possibility of creating phosphenes by the coronacurrents developing from the head of a person located close to alightning strike is investigated. The results show that themagnitude of the electric fields induced in the brain by coronacurrents are comparable to those generated by TMS. This inturn shows that the corona currents generated by long durationlightning flashes could excite phosphenes through theirinteraction with the visual cortex or retina in a human located inthe vicinity of the lightning channel. It is suggested that some ofthe ball lightning observations reported in the literature could beluminous perceptions caused by the interaction of the coronacurrents with the visual cortex or retina of a person located inthe vicinity of a lightning strike.
|
|
| 6. |
- Cooray, Vernon, et al.
(author)
-
Electric field of a relativistic electron avalanche
- 2012
-
In: 2012 31st International Conference on Lightning Protection, ICLP 2012. - 9781467318976 ; , s. 6344240-
-
Conference paper (peer-reviewed)abstract
- In the present study, electromagnetic fields of accelerating charges were utilized to evaluate the electromagnetic fields generated by a relativistic electron avalanche. In the analysis it is assumed that all the electrons in the avalanche are moving with the same speed. In other words, the growth or the decay of the number of electrons takes place only at the head of the avalanche. It is shown that the radiation is emanating only from the head of the avalanche where electrons are being accelerated. It is also shown that an analytical expression for the radiation field of the avalanche at any distance can be written directly in terms of the e-folding length of the avalanche. This makes it possible to extract directly the spatial variation of the e-folding length of the avalanche from the measured radiation fields.
|
|
| 7. |
- Cooray, Vernon, et al.
(author)
-
Electromagnetic fields of a relativistic electron avalanche with special attention to the origin of lightning signatures known as narrow bipolar pulses
- 2014
-
In: Atmospheric research. - : Elsevier BV. - 0169-8095 .- 1873-2895. ; 149, s. 346-358
-
Journal article (peer-reviewed)abstract
- In the present study, electromagnetic fields of accelerating charges were utilized to evaluate the electromagnetic fields generated by a relativistic electron avalanche. In the analysis it is assumed that all the electrons in the avalanche are moving with the same speed. In other words, the growth or the decay of the number of electrons takes place only at the head of the avalanche. It is shown that the radiation is emanating only from the head of the avalanche where electrons are being accelerated. It is also shown that an analytical expression for the radiation field of the avalanche at any distance can be written directly in terms of the e-folding length of the avalanche. This model of the avalanche was utilized to test the idea whether the source of the lightning signatures known as narrow bipolar pulses could be relativistic avalanches. The idea was tested by using the simultaneously measured electric fields of narrow bipolar pulses at two distances, one measured far away from the source and the other in the near vicinity. The avalanche parameters were extracted from the distant field and they are used to evaluate the close field. The results show that the source of the NBP can be modeled either as a single or a multiple burst of relativistic avalanches with speed of avalanches in the range of 2-3 x 10(8) m/s. The multiple avalanche model agrees better with the experimental data in that it can also generate the correct signature of the time derivatives and the HF and VHF radiation bursts of NBP.
|
|
| 8. |
- Cooray, Vernon, et al.
(author)
-
Electromagnetic radiation field of an electron avalanche
- 2012
-
In: Atmospheric research. - : Elsevier BV. - 0169-8095 .- 1873-2895. ; 117:SI, s. 18-27
-
Journal article (peer-reviewed)abstract
- Electron avalanches are the main constituent of electrical discharges in the atmosphere. However, the electromagnetic radiation field generated by a single electron avalanche growing in different field configurations has not yet been evaluated in the literature. In this paper, the electromagnetic radiation fields created by electron avalanches were evaluated for electric fields in pointed, co-axial and spherical geometries. The results show that the radiation field has a duration of approximately 1–2 ns, with a rise time in the range of 0.25 ns. The wave-shape takes the form of an initial peak followed by an overshoot in the opposite direction. The electromagnetic spectrum generated by the avalanches has a peak around 109 Hz.
|
|
| 9. |
- Cooray, Vernon, et al.
(author)
-
Excitation of visual sensory experiences by electromagnetic fields of lightning
- 2012
-
In: Lightning Electromagnetics. - : IET. - 9781849192156
-
Book chapter (peer-reviewed)abstract
- In this chapter, we will consider the possible interactions, either direct or indirect, of the lightning-generated electromagnetic fields with the brain or the visual system of humans to induce visual sensations. Some of these visual sensations are known as phosphenes in the medical literature. Since some of these visual sensations could be misinterpreted as ball lightning, this subject is of interest for lightning researchers due to the still unsolved problem of the origin of ball lightning.
|
|
| 10. |
- Cooray, Vernon, et al.
(author)
-
On the electric and magnetic fields below a single conductor overhead power line
- 2012
-
In: 2012 31st International Conference on Lightning Protection, ICLP 2012. - 9781467318976 ; , s. 6344307-
-
Conference paper (peer-reviewed)abstract
- Electromagnetic fields associated with the electric current flowing along a overhead power line with a single conductor located over perfectly conducting ground are estimated using electromagnetic fields pertinent to acceleration of electric charges. It is shown that the electric and magnetic fields that exist below a long overhead power line are nothing but the radiation fields generated by the acceleration of charge at the point of injection of current into the power line.
|
|
| 11. |
- Cooray, Vernon, et al.
(author)
-
On the possibility of phosphenes being generated by the energetic radiation from lightning flashes and thunderstorms
- 2011
-
In: Physics Letters A. - : Elsevier BV. - 0375-9601 .- 1873-2429. ; 375:42, s. 3704-3709
-
Journal article (peer-reviewed)abstract
- After the first report of this phenomenon by Apollo 11 astronauts, experiments conducted in space and on the ground confirmed the creation of phosphenes by the interaction of energetic radiation with the human visual system. The aim of this Letter is to show that the energetic radiation generated in the form of X-rays, gamma rays, electrons and neutrons by thunderstorms and lightning is strong enough for the creation of phosphenes in humans. It is also pointed out that some of the visual observations reported during thunderstorms might be attributable to phosphenes excited by this energetic radiation.
|
|
| 12. |
- Cooray, Vernon, et al.
(author)
-
On the streamer discharges emitted from the head of a person located in the vicinity of lightning strikes and their possible consequences
- 2013
-
In: Journal of Electrostatics. - : Elsevier BV. - 0304-3886 .- 1873-5738. ; 71:3, s. 572-576
-
Journal article (peer-reviewed)abstract
- In this paper the currents associated with the streamer discharges generated from the head of a person located in the vicinity of a lightning strike are investigated. In the analysis the location of the person with respect to the lightning strike is selected in such a way that only a streamer burst, without the formation of a connecting leader, is emitted from the head. The current associated with these streamer bursts could exceed several hundreds of mA and may last for several hundreds of microseconds. The results of the calculation show that the passage of the streamer currents through the body of the person could create electric fields in the brain large enough to excite neurons. Depending on the strength of lightning flash and the distance to the strike point these streamer bursts can give rise to phosphenes which are a form of visual experience that occurs when the visual cortex is stimulated by electric currents.
|
|
| 13. |
- Cooray, Vernon, et al.
(author)
-
The Electromagnetic Fields of an Accelerating Charge : Applications in Lightning Return-Stroke Models
- 2010
-
In: IEEE transactions on electromagnetic compatibility (Print). - 0018-9375 .- 1558-187X. ; 52:4, s. 944-955
-
Journal article (peer-reviewed)abstract
- In the literature, three procedures have been used to calculate the electromagnetic fields from return strokes. In the first technique, the source is described only in terms of current density and the fields are expressed entirely in terms of the return-stroke current. In the second technique, the source is expressed in terms of the current and the charge densities and the fields are given in terms of both the current and the charge density. In the third technique, the fields are expressed in terms of the apparent charge density. The fields are connected to the source terms through the vector and scalar potentials. In this paper, the standard equations for the electromagnetic fields generated by an accelerating charge are utilized to evaluate the electromagnetic fields from lightning return strokes. It is shown that the total fields evaluated at any distance using these expressions are identical to those obtained using other techniques. However, the composition of the terms that vary as 1/R, 1/R2, and 1/R3 of the total electric field is different from those of other formulations. In the case of the transmission-line model, where the return stroke is described as a current pulse propagating with uniform velocity, radiation emanates only from the bottom of the channel where current is generated. When the speed of propagation is equal to the speed of light, the total field throughout the entire space becomes radiation. The procedure is also applied here to obtain the electric fields of the traveling-current-source model. The electric fields obtained for this case, too, agree with the previous study. It is also shown how the equations can be applied rather conveniently to evaluate: 1) the electromagnetic fields generated by current pulses propagating along overhead power lines; and 2) the electromagnetic fields generated by vertical conductors and towers during lightning strikes.
|
|
| 14. |
|
|
| 15. |
- Ahmad, Mohd Riduan, et al.
(author)
-
Chaotic Pulse Train in Cloud-to-Ground and Cloud Flashes of Tropical Thunderstorms
- 2014
-
Conference paper (peer-reviewed)abstract
- In this paper, we report for the first time the observation of chaotic pulse train (CPT) preceding natural subsequent negative return strokes and also CPT occurrence in IC flashes from tropical thunderstorms in South Malaysia. In CG flashes, all CPTs were occurred in between return strokes with 41.1% have occurred between the first and second return strokes. The maximum number of CPT in one sequence is 3, which can be observed between the first and third return strokes only. In IC flashes, all CPTs were observed to occur in between IC flash pulses.
|
|
| 16. |
|
|
| 17. |
- Ahmad, Mohd Riduan, 1980-
(author)
-
Interaction of Lightning Flashes with Wireless Communication Networks : Special Attention to Narrow Bipolar Pulses
- 2014
-
Doctoral thesis (other academic/artistic)abstract
- In this thesis, the features of electric field signatures of narrow bipolar pulses (NBPs) generated by cloud flashes are investigated and their effects on wireless communication systems are studied. A handful amount of NBPs (14.5%) have been observed to occur as part of cloud-to-ground flashes in South Malaysia. Occurrence of NBPs in Sweden has been reported for the first time in this thesis. The electric field waveform characteristics of NBPs as part of cloud-to-ground flashes were similar to isolated NBPs found in Sweden and South Malaysia and also to those isolated NBPs reported by previous studies from various geographical areas. This is a strong indication that their breakdown mechanisms are similar at any latitudes regardless of geographical areas.A comparative study on the occurrence of NBPs and other forms of lightning flashes across various geographical areas ranging from northern regions to the tropics is presented. As the latitude decreased from Uppsala, Sweden (59.8°N) to South Malaysia (1.5°N), the percentage of NBP emissions relative to the total number of lightning flashes increased significantly from 0.13% to 12%. Occurrences of positive NBPs were more common than negative NBPs at all observed latitudes. However, as latitudes decreased, the negative NBP emissions increased significantly from 20% (Sweden) to 45% (South Malaysia). Factors involving mixed-phase region elevations and vertical extents of thundercloud tops are invoked to explain the observed results. These factors are fundamentally latitude dependent.In this thesis, the interaction between microwave radiations emitted by cloud-to-ground and cloud flashes events and bits transmission in wireless communication networks are also presented. To the best of our knowledge, this is the first time such effects are investigated in the literature. Narrow bipolar pulses were found to be the strongest source of interference that interfered with the bits transmission.
|
|
| 18. |
- Ahmad, Mohd Riduan, et al.
(author)
-
Interference from cloud-to-ground and cloud flashes in wireless communication system
- 2014
-
In: Electric power systems research. - : Elsevier BV. - 0378-7796 .- 1873-2046. ; 113, s. 237-246
-
Journal article (peer-reviewed)abstract
- In this study, cloud-to-ground (CG) flash and intra-cloud (IC) flash events that interfere with the transmission of bits in wireless communication system operating at 2.4 GHz were analyzed. Bit error rate (BER) and consecutive lost datagram (CLD) measurement methods were used to evaluate BER and burst error from 3 tropical thunderstorms on November 27, 28, and 29 during 2012 northeastern monsoon in Malaysia. A total of 850 waveforms from the electric field change recording system were recorded and examined. Out of these, 94 waveforms of very fine structure were selected which matched perfectly with the timing information of the recorded BER. We found that both CG and IC flashes interfered significantly with the transmission of bits in wireless communication system. The severity of the interference depends mainly on two factors namely the number of pulses and the amplitude intensity of the flash. The interference level becomes worst when the number of pulses in a flash increases and the amplitude intensity of pulses in a flash intensifies. During thunderstorms, wireless communication system has experienced mostly intermittent interference due to burst error. Occasionally, in the presence of very intense NBP event, wireless communication system could experience total communication lost. In CG flash, it can be concluded that PBP is the major. source of interference that interfered with the bits transmission and caused the largest burst error. In IC flash, we found that the typical IC pulses interfered the bits transmission in the same way as PBP and mixed events in CG flash and produced comparable and in some cases higher amount of burst error. NBP has been observed to interfere the bits transmission more severely than typical IC and CG flashes and caused the most severe burst error to wireless communication system.
|
|
| 19. |
- Ahmad, Mohd Riduan, et al.
(author)
-
Lightning interference in multiple antennas wireless communication systems
- 2012
-
In: Journal of Lightning Research. - : Bentham open. - 1652-8034. ; 4, s. 155-165
-
Journal article (peer-reviewed)abstract
- This paper analyzes the interference of lightning flashes with multiple antennas wireless communicationsystems operating in the microwave band at 2.4 GHz and 5.2 GHz. A bit error rate (BER) measurement method was usedto evaluate BER and packet error rate (PER) during 5 heavy thunderstorms on January 25 and March 17 to 20, 2011,respectively. In addition, BER measurements also were done on January 21 and March 30, 2011 under fair weather (FW)conditions providing a baseline for comparison. The Transmitter-Receiver separation was fixed at 10 meter with line-ofsight(LOS) consideration. We infer that lightning interfered with the transmitted digital pulses which resulted in a higherrecorded BER. The maximum recorded BER was 9.9·10-1 and the average recorded BER and PER were 2.07·10-2 and2.44·10-2 respectively during the thunderstorms with the average fair weather BER and PER values under the influence ofadjacent channel interference (ACI) and co-channel interference (CCI) being 1.75·10-5 and 7.35·10-6 respectively. Weconclude that multiple antennas wireless communication systems operating at the microwave frequency can besignificantly interfered by lightning.
|
|
| 20. |
- Ahmad, M R, et al.
(author)
-
Measurement of bit error rate at 2,4 GHz due to lightning interference
- 2012
-
In: Proceeding of the 31st International Conference on Lightning Protection ICLP 2012. - 9781467318976
-
Conference paper (peer-reviewed)abstract
- This paper analyzes the interference of lightning flashes with wireless communication systems operating in the microwave band at 2.4 GHz. A bit error rate (BER) measurement method was used to evaluate BER during 3 heavy thunderstorms on January 25, March 17 and March 20, all in year 2011. In addition, BER measurements also were done on January 21 and March 30, 2011 under fair weather (FW) conditions providing a baseline for comparison. The Transmitter-Receiver separation was fixed at 10 meter with line-of-sight (LOS) consideration. We infer that lightning interfered with the transmitted digital pulses which resulted in a higher recorded BER. The maximum recorded BER was 9.9·101 and the average recorded BER was 9.95·10 -3 during the thunderstorms with the average fair weather BER values under the influence of adjacent channel interference (ACI) and co-channel interference (CCI) being 1.75·10-5 and 7.35·10 -6 respectively. We conclude that wireless communication systems operating at 2.4 GHz microwave frequency can be significantly interfered by lightning.
|
|
| 21. |
|
|
| 22. |
|
|
| 23. |
|
|
| 24. |
- Ahmad, Mohd Riduan, et al.
(author)
-
Preliminary Observations of Lightning Signature At 2400 MHz in Sweden Thunderstorm
- 2012
-
Conference paper (peer-reviewed)abstract
- This paper presents a preliminary observation of lightning signature at 2400 MHz. We believe this is the first time such observation was made in such frequency band. One positive ground discharge and one cloud discharge waveforms have been selected from a collection of waveforms recorded using fast and slow broadband antenna systems. In addition, waveforms recorded directly from 2400 MHz whip antenna associated with the selected ground and cloud discharges waveforms were observed. The measurements were carried out in Uppsala, Sweden in July 2012. We discovered a possible lightning signature at 2400 MHz with the existence of bursts of pulses happened to occur simultaneously with preliminary breakdown, negative return stroke and cloud pulses. These bursts of pulses possibly interfered in some ways with the transmitted bits leading to higher recorded error bits during the thunderstorm.
|
|
| 25. |
- Ahmad, Mohd Riduan, et al.
(author)
-
Similarity between the Initial Breakdown Pulses of Negative Ground Flash and Narrow Bipolar Pulses
- 2014
-
In: 2014 INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP). - : IEEE conference proceedings. - 9781479935444 ; , s. 810-813
-
Conference paper (peer-reviewed)abstract
- In this paper, temporal characteristics of several initial electric field pulses of preliminary breakdown process (PBP) from very close negative cloud-to-ground (CG) flashes are compared to close narrow bipolar pulses (NBPs) to observe any similarity that may exists. Interestingly, we found that the initial PBP pulses are similar to close NBP with zero crossing time less than 5 mu s, do not preceded by any slow field change and followed by pronounce static component. As NBPs are believed to be a result of relativistic runaway electron avalanches discharge, this finding is an indication that the initial electric field pulses of PBP are perhaps the result of the same discharge mechanism.
|
|
| 26. |
- Ahmad, Noor Azlinda, 1978-
(author)
-
Broadband and HF Radiation from Cloud Flashes and Narrow Bipolar Pulses
- 2011
-
Doctoral thesis (other academic/artistic)abstract
- Remote measurement of electric field generated by lightning has played a major role in understanding the lightning phenomenon. Even though other measurements such as photographic and channel base current have contributed to this research field, due to practical reasons remote measurements of electric field is considered as the most useful tool in lightning research. This thesis discusses the remotely measured radiation field component of electric field generated by cloud flashes (ICs) and narrow bipolar pulses (NBPs). The associated HF radiation of these events at 3 MHz and 30 MHz are also discussed. To understand the initiation process of these discharges, a comparative study of the initial pulse of cloud flashes against the initial pulse of cloud to ground flashes was conducted. The result suggests that both discharges might have been initiated by similar physical processes inside the thunderclouds. Comparing the features of initial pulse of cloud and ground flashes with that of pulses that appeared in the later stages of cloud flashes suggests that the initiation process involved in both flashes are not very much different from the initiation of cloud flashes at the later stage. The average spectral amplitudes of electric field of full duration cloud flashes (180 ms) showed f -1 frequency dependence within the interval of 10 kHz to approximately 10 MHz. This is in contrast to the standard f -2 decrement (or even steeper ) at high frequency region for other lightning processes such as return strokes. It was suggested that small pulses which repeatedly appeared at the later stage of cloud flashes might have contributed to enhance the spectral amplitude at higher frequencies. Electric fields generated by Narrow Bipolar Pulses (NBPs), which are considered as one of the strongest sources of HF radiation, were measured in the tropics of Malaysia and Sri Lanka. Their features were also studied and show a good agreement with previously published observations of NBPs from other geographical regions. Thorough analyses and observations of these pulses found previously unreported sharp, fine peaks embedded in the rising and decaying edge of the electric field change of NBPs. Therefore it was suggested that these fine peaks are mostly responsible for the intense HF radiation at 30 MHz.
|
|
| 27. |
- Ahmad, Noor Azlinda, et al.
(author)
-
Characteristics of narrow bipolar pulses observed in Malaysia
- 2010
-
In: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826 .- 1879-1824. ; 72:5-6, s. 534-540
-
Journal article (peer-reviewed)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.
|
|
| 28. |
|
|
| 29. |
- Ahmad, Noor Azlinda, et al.
(author)
-
The first electric field pulse of cloud and cloud-to-ground lightning discharges
- 2010
-
In: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826 .- 1879-1824. ; 72:2-3, s. 143-150
-
Journal article (peer-reviewed)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.
|
|
| 30. |
- Arevalo, Liliana, 1978-, et al.
(author)
-
A new static calculation of the streamer region for long spark gaps
- 2012
-
In: Journal of Electrostatics. - : Elsevier BV. - 0304-3886 .- 1873-5738. ; 70:1, s. 15-19
-
Journal article (peer-reviewed)abstract
- Different electrostatic approximations have been proposed to calculate the streamer region without going in deep details of the behavior of density of particles under the effect of high electric fields; this kind of approximations have been used in numerical calculations of long spark gaps and lightning attachment. The simplifications of the streamer region are achieved by considering it to be a geometrical region with a constant geometrical shape. Different geometrical shapes have been used, such as cones or several parallel filaments. Afterward, to simplify the procedures, the streamer region was approximated by two constants, one denoted K-Q, called the geometrical constant and in other cases K named as geometrical factor. However, when a voltage that varies with time is applied to an arrangement of electrodes (high voltage and grounded electrodes), the background electric field will change with time. Thus, if the background electric field is modified, the streamer zone could cover a larger or smaller area. With the aim of reducing the number of assumptions required in the calculation of long gap discharges, a new electrostatic model to calculate the streamer region is presented. This model considers a variable streamer zone that changes with the electric field variations. The three-dimensional region that fulfills the minimum electric field to sustain a streamer is identified for each time step, and the charge accumulated in that region is then calculated. The only parameter that is being used in the calculation is the minimum electric field necessary for the propagation of streamers.
|
|
| 31. |
|
|
| 32. |
- Arevalo, L., et al.
(author)
-
Corona charge produced by thundercloud fields in grounded rods
- 2012
-
In: 31st International Conference on Lightning Protection ICLP 2012. - 9781467318976 ; , s. 6344365-
-
Conference paper (peer-reviewed)abstract
- Electrostatic fields below the thundercloud lead to the formation of glow charge from grounded objects. The charge accumulated after certain time can initiate or inhibit the called streamer formation and consequently the inception and development of upward leaders. By means of a two dimensional numerical model that takes into account the particles behavior is observed that glow charge can smooth the electric field on top of the grounded rod and consequently hinder the inception of streamers and upward leaders from the grounded rod. It is concluded that to be able to initiate unstable upward leaders from the shielded grounded rod a sudden change of electric field is necessary. A two dimensional numerical model that solves the continuity equations for positive and negative ions and electrons coupled with Poisson equation was implemented. Comparison for different magnitudes of electric field and characteristics of rod are included as well.
|
|
| 33. |
|
|
| 34. |
- Arevalo, Liliana, 1978-
(author)
-
Numerical Simulations of Long Spark and Lightning Attachment
- 2011
-
Doctoral thesis (other academic/artistic)abstract
- The research work presented here is concerned with numerical simulations of two different electrical phenomena: Long gap electrical discharges under switching impulses and the lightning attachment process associated with positive upward leaders. The development of positive upward leaders and the progression of discharges in long gaps are attributable to two intertwined physical phenomena, namely, the leader channel and the streamer zone. The physical description and the proposed calculations of the above-mentioned phenomena are based on experimental tests conducted in long spark gaps. The methodology presented here proposes a new geometrical approximation for the representation of the streamer and the calculation of the accumulated electrical charge. Furthermore, two different approaches to representing the leader channel are applied and compared. Statistical delays before the inception of the first corona, and random distributions to represent the tortuous nature of the path taken by the leader channel were included based on the behavior observed in experimental tests, with the intention of ensuring the discharge behaved in a realistic manner. A reasonable agreement was found between the physical model and the experimental test results. A model is proposed to simulate the negative discharges produced by switching impulses using the methodology developed to simulate positive leader discharges and the physics underlying the negative leader phenomena. The validation of the method demonstrated that phenomena such as the pilot leader and negative leader currents are successfully represented. In addition, based on previous work conducted on the physics of lightning and the lightning attachment process, a new methodology is developed and tested. In this new approach, the background electric field and the ionized region, considered in conjunction with the advance of the leader segment, are computed using a novel method. The proposed methodology was employed to test two engineering methods that are accepted in international standards, the mesh method and the electro-geometrical method. The results demonstrated that the engineering approximations are consistent with the physical approach. In addition to the electrical phenomena mentioned above, one should remember that, to simplify the calculation, there are certain real effects arising from the lightning attachment process that have not been considered. In fact, when a structure is subjected to a strong electric field, it is possible to generate multiple upward leaders from that structure. This effect has not been taken into account in the numerical models available previously, and therefore the process of generating multiple upward leaders incepted over a structure is incorporated here. The results have shown that a slight advantage from the background electric field is enough for one upward connecting leader to take over, thereby forcing the others to abort the attachment process.
|
|
| 35. |
- Arevalo, Liliana, et al.
(author)
-
On the interception of lightning flashes by power transmission lines
- 2011
-
In: Journal of Electrostatics. - : Elsevier BV. - 0304-3886 .- 1873-5738. ; 69:3, s. 220-227
-
Journal article (peer-reviewed)abstract
- The design of the lightning protection system LPS of transmission lines is based on the well knownelectro-geometrical model. The electro-geometrical model assumes that the first point on a powertransmission line that will come within striking distance of the tip of a down-coming stepped leaderchannel is the strike point of the lightning flash. The model neglects almost all of the physics associatedwith the lightning attachment.Nowadays, as it is possible to use modern hardware and software tools and several different numericalmethods, it is feasible to apply the physics of the discharge process to the study of lightning attachment.Such models take into account the movement of the downward and the resulting upward leaders fromdifferent points on the structures under consideration.In this paper, a procedure based on lightning physics was used to analyze the lightning attachmentphenomena in EHV transmission lines of 230 kV and 500 kV and the results were compared with thepredictions of the electro-geometrical method.
|
|
| 36. |
- Arevalo, Liliana, et al.
(author)
-
Preliminary study on the modelling of negative leader discharges
- 2011
-
In: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 44:31, s. 315204-
-
Journal article (peer-reviewed)abstract
- Nowadays, there is considerable interest in understanding the physics underlying positive and negative discharges because of the importance of improving lightning protection systems and of coordinating the insulation for high voltages. Numerical simulations of positive switching impulses made in long spark gaps in a laboratory are achievable because the physics of the process is reasonably well understood and because of the availability of powerful computational methods. However, the existing work on the simulation of negative switching discharges has been held up by a lack of experimental data and the absence of a full understanding of the physics involved. In the scientific community, it is well known that most of the lightning discharges that occur in nature are of negative polarity, and because of their complexity, the only way to understand them is to generate the discharges in laboratories under controlled conditions. The voltage impulse waveshape used in laboratories is a negative switching impulse. With the aim of applying the available information to a self-consistent physical method, an electrostatic approximation of the negative leader discharge process is presented here. The simulation procedure takes into consideration the physics of positive and negative discharges, considering that the negative leader propagates towards a grounded electrode and the positive leader towards a rod electrode. The simulation considers the leader channel to be thermodynamic, and assumes that the conditions required to generate a thermal channel are the same for positive and negative leaders. However, the magnitude of the electrical charge necessary to reproduce their propagation and thermalization is different, and both values are based on experimental data. The positive and negative streamer development is based on the constant electric field characteristics of these discharges, as found during experimental measurements made by different authors. As a computational tool, a finite element method based software is employed. The simulations are compared with experimental data available in the literature.
|
|
| 37. |
|
|
| 38. |
- Arevalo, Liliana, et al.
(author)
-
Streamer to leader transition criteria for propagation of long sparks and lightning leaders
- 2014
-
In: 2014 INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP). - : IEEE conference proceedings. - 9781479935444 ; , s. 480-483
-
Conference paper (peer-reviewed)abstract
- Certain models have been dedicated to analyze the breakdown of long spark gaps and the lightning attachment process based on the mechanism of leader propagation. One of the most important processes on the mechanism of leader is the transition between streamers to leader. The streamer to leader transition is characterized by a rapid increase in the electron density and gas temperature, which is a consequence of the onset of thermal-ionization instability. To simplify the complexity of the physical process lightning attachment and long spark gaps models assumed that a minimum charge of 1 mu C is necessary to thermalize a leader channel, independently of the electric field and atmospheric conditions as temperature, pressure and humidity. In this paper an approach that takes into account the continuity equations and the gas temperature balance equation is used to investigate the minimum charge required to start the streamer to leader transition. The obtained results are compared with the minimum charge criteria used for long spark gaps and lightning attachment modeling. Simulation shows that the required charge to thermalize a leader depends on the vibrational energy relaxation. Results also indicate that only a small part of the energy input, transferred by electrons to gas molecules in the stem, contributes immediately to the temperature rise.
|
|
| 39. |
- Arevalo, Liliana, et al.
(author)
-
'The mesh method' in lightning protection standards - Revisited
- 2010
-
In: Journal of Electrostatics. - : Elsevier BV. - 0304-3886 .- 1873-5738. ; 68:4, s. 311-314
-
Journal article (peer-reviewed)abstract
- At present the design of the Lightning protection systems (LPS) for structures as stipulated in standards is based on the electro - geometrical method, which was initially used to protect power lines from lightning. A derivative of the electro-geometrical method is the rolling sphere method. This method together, with the protection angle method and mesh method are used almost in all lightning standards as the measure in installing the lightning protection systems of grounded structures. In the mesh method, the dimension of the cell size in different levels of protection is determined using the rolling sphere method. Since the rolling sphere method does not take into account the physics of the lightning attachment process there is a need to evaluate the validity of the stipulated value in standards of the minimum lightning current that can penetrate through the mesh in different levels of protection. In this paper, meshes of different sizes as stipulated in the lightning protection standards were tested for their ability to intercept lightning flashes using a lightning attachment model that takes into account the physics of connecting leaders on. The results are in reasonable agreement with the specifications given in the lightning protection standards.
|
|
| 40. |
- Arevalo, Liliana, et al.
(author)
-
Upward leader inception caused by a sudden change of cloud electric field
- 2014
-
In: 2014 INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP). - : IEEE conference proceedings. - 9781479935444 ; , s. 484-487
-
Conference paper (peer-reviewed)abstract
- Discharge processes such as glow, streamer, and leader inception among others take place before an upward leader can be launched from a grounded structure during thunderstorms. Electrostatic fields below the thundercloud could lead to the formation of glow charge from grounded objects. If the electric field is high enough and ionization keeps expanding into the gap, streamers can be incepted. Depending on the available charge and the thermodynamic properties of the gas, there is a possibility to incept or not a positive upward leader towards the cloud. Usually, the inception of positive upward leaders is directly related with the appearance of a downward coming leader from cloud towards the grounded object. Such a downward leader will intensify the electric field in such a way that the streamer discharges could thermalize and produce an unstable upward leader channel. However, experimental observations have indicated the inception of upward leaders from grounded structures without registering connecting downward leaders towards the structure. The present paper intends to explain the inception of positive upward leaders from the top of a rod, whenever the electric field produced by the cloud suddenly changes e.g. due to intra-cloud discharges or distance cloud to ground flash. A two dimensional model based on the gas-dynamic equations, the main processes responsible for gas heating such as vibrational excitation and transfer of energy into electronic, rotational and translational excitation, coupled with Poisson equation is presented in this paper. Rods of different lengths under thundercloud electric field were studied. Simulation results indicate that positive upward leaders can be incepted from long rods under certain conditions of thundercloud electric field without the need of a coming downward leader. However, for rods of tenths of meters the thundercloud electric field is not enough to incept positive upward leaders and an intensification of the electric field is required in order to incept a positive upward leader from the structure, e.g., a coming downward leader.
|
|
| 41. |
- Baharudin, Zikri Abadi
(author)
-
Characterizations of ground flashes from tropic to northern region
- 2014
-
Artistic work (other academic/artistic)abstract
- This thesis portrays new information concerning the cloud-to-ground (CG) lightning flashes or ground flashes produced by thunderclouds. It emphasizes the importance of characterizing lightning studies as the relationship between lightning mechanisms, and of incorporating the influence of geographical location, latitude and storm type. Sweden, Malaysia and USA were chosen as the main locations for field experiments in 2009 to 2011 to gather a significant number of negative and positive CG flashes. This work provided data on a total of 1792 CG lightning flashes (1685 negative and 107 positive ones) from a total of 53 thunderstorms by monitoring both the slow and the fast electric field and the narrowband radiation field at 3 and 30 MHz signals simultaneously. This thesis is comprised of: (i) the relationship of the Low Positive Charge Region (LPCR) and Preliminary Breakdown Pulse (PBP) trains to the occurrence of negative CG, (ii) slow field changes generated by preliminary breakdown processes in positive and negative ground flashes, and (iii) the occurrence of positive and negative ground flashes. It was revealed that the PBP train appeared have a higher strength in the in Sweden. The strength of the PBP train was caused by the LPCR; in contrast, weak PBP trains were characteristic in tropical countries constituting insignificant LPCR and needing little energy to break the “blocking” agent to allow the flash to propagate downward to the ground. The second contribution concerns the characteristics of the PBP train mentioned; this includes novel information for Malaysia. Further, it is stated that there are some different characteristics in the PBP trains in Johor, Malaysia and Florida, USA. The studies of slow field changes generated by preliminary breakdown processes clarifies unclear features concerning the starting position of slow field changes generated by preliminary breakdown processes in positive and negative ground flashes. It was found that the slow field changes did not occur before the initial process of the commencement of preliminary breakdown. Single-station electric field measurements incorporating narrowband radiation field measurement and high resolution transient recording (12 bits) with an accuracy of several nanoseconds, allows one to distinguish between the intracloud activities and the preceding processes of ground flashes. The results for the interstroke intervals, amplitude distribution of subsequent return-stroke (SRS) and the number of strokes per flash in the tropics, subtropics and northern regions were similar. Finally, a significant number of positive return-stroke (RS) electric fields provided statistically significant information on the characteristics of these strokes.
|
|
| 42. |
- Baharudin, Zikri A., et al.
(author)
-
Comparative study on preliminary breakdown pulse trains observed in Johor, Malaysia and Florida, USA
- 2012
-
In: Atmospheric research. - : Elsevier BV. - 0169-8095 .- 1873-2895. ; 117, s. 111-121
-
Journal article (peer-reviewed)abstract
- In this paper, the preliminary breakdown (PB) pulse train preceding the negative first return stroke (RS) is recorded using a broad band antenna system. These analyses were carried out in Johor Bahru, Malaysia and Florida, United States. This is a novel initiative at examining and identifying the characteristics of the PB pulse trains in the negative cloud-to-ground flashes observed in Malaysia. The arithmetic mean of the total pulse train duration is 12.3 ms and the weighted arithmetic mean of the pulse durations and interpulse intervals are 11 mu s and 152 mu s, respectively. The arithmetic mean ratio between the maximum peak amplitude of the PB pulse and the peak RS electric field was 27.8%, and the corresponding value in Florida was 29.4%. The arithmetic mean of the time duration between the most active part of the pulse train, and the RS was 57.6 ms in Malaysia and 22 ms in Florida. A qualitative comparison of our results with those obtained earlier in Sri Lanka. Sweden and Finland supports the hypothesis that the PBP/RS ratio is higher in the northern regions compared to the tropical regions. (C) 2012 Elsevier B.V. All rights reserved.
|
|
| 43. |
|
|
| 44. |
- Baharudin, Zikri A., et al.
(author)
-
Electric field changes generated by the preliminary breakdown for the negative cloud-to-ground lightning flashes in Malaysia and Sweden
- 2012
-
In: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826 .- 1879-1824. ; 84-85, s. 15-24
-
Journal article (peer-reviewed)abstract
- We present the study of the electric field changes generated by the preliminary breakdown for negative cloud-to-ground lightning flashes in Malaysia and Sweden concerning the association of slow field changes associated in preliminary breakdown process. We examined the total of 1685 negative cloud-to-ground lightning flashes from the total of 39 thunderstorms by recording the slow electric field, fast electric field and narrowband radiation field at 3 and 30 MHz signals simultaneously. Our results show that there is a pre-starting time, i.e. the duration between the first preliminary breakdown pulse and slow field changes starting point, which is found to be after the first preliminary breakdown pulse. The pre-starting time has the arithmetic and geometric mean range from 1.4-6.47 and 1-3.36 ms, respectively. The mean values of pre-starting time in Malaysia are greater than the values observed in Sweden by more than a factor of 3. From the two data sets it shows that the slow field changes never start before the preliminary breakdown. Furthermore, the use of single-station electric fields measurement with high resolutions of 12 bits transient recorder with several nanosecond accuracy allow one to distinguish the slow field changes generated by preliminary breakdown, which preceded the negative first return stroke, between tens to hundreds of milliseconds of pre-return stroke duration.
|
|
| 45. |
- Baharudin, Zikri A., et al.
(author)
-
Negative cloud-to-ground lightning flashes in Malaysia
- 2014
-
In: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826 .- 1879-1824. ; 108, s. 61-67
-
Journal article (peer-reviewed)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.
|
|
| 46. |
- Bodhika, J. A. P., et al.
(author)
-
A preliminary study on characteristics of thunder pulses of lightning
- 2014
-
In: 2014 INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP). - : IEEE conference proceedings. - 9781479935444 ; , s. 260-264
-
Conference paper (peer-reviewed)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.
|
|
| 47. |
- Bodhika, J. A. P., et al.
(author)
-
Reconstruction of lightning channel geometry by localizing thunder sources
- 2013
-
In: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826 .- 1879-1824. ; 102, s. 81-90
-
Journal article (peer-reviewed)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.
|
|
| 48. |
|
|
| 49. |
|
|
| 50. |
- Cooray, Vernon
(author)
-
Attachment of lightning flashes to grounded structures
- 2012
-
In: Lightning Electromagnetics. - : IET. - 9781849192156 ; , s. 765-787
-
Book chapter (peer-reviewed)abstract
- A grounded structure can interact with a lightning flash in two different ways. It can interact with either a downward or an upward lightning flash. The initiation of a downward lightning flash takes place in the cloud, whereas in the case of upward lightning flash, the point of initiation is usually at the tip of a tall structure. In other words, upward lightning flashes are created by the grounded structure itself. In this chapter, a brief description of various models used to study the lightning attachment is given together with some of their predictions.
|
|
