| 1. |
- Cooray, Vernon, 1952-, et al.
(författare)
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Comment on "Straight lightning as a signature of macroscopic dark matter"
- 2022
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Ingår i: Physical Review D. - : American Physical Society. - 2470-0010 .- 2470-0029. ; 105:8
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- In the discussed paper [N. Starkman, H. Winch, J. S. Sidhu, and G. Starkman, Straight lightning as a signature of macroscopic dark matter, Phys. Rev. D 103, 063024 (2021)], the authors have made several assumptions and statements concerning the initiation and propagation of lightning flashes induced by macroscopic dark matter passing through the atmosphere. The authors suggest that the path of dark matter can be identified by looking for lightning with straight channels, although such channels have not been previously reported. Even though we agree with the suggestion of the authors that macroscopic dark matter could, in theory, give rise to straight lightning channels, there are several statements in the paper that are not sufficiently clear and which could lead to misinterpretation. Our comments on the paper are the following.
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| 2. |
- Cooray, Vernon, 1952-, et al.
(författare)
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Could Macroscopic Dark Matter (Macros) Give Rise to Mini-Lightning Flashes out of a Blue Sky without Clouds?
- 2021
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Ingår i: Atmosphere. - : MDPI. - 2073-4433. ; 12:9
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Tidskriftsartikel (refereegranskat)abstract
- A recent study pointed out that macroscopic dark matter (macros) traversing through the Earth's atmosphere can give rise to hot and ionized channels similar to those associated with lightning leaders. The authors of the study investigated the possibility that when such channels created by macros pass through a thundercloud, lightning leaders may be locked in by these ionized channels, creating lightning discharges with perfectly straight channels. They suggested the possibility of detecting such channels as a means of detecting the passage of macros through the atmosphere. In this paper, we show that such macros crossing the atmosphere under fair weather conditions could also give rise to mini-lightning flashes with current amplitudes in the order of a few hundred Amperes. These mini-lightning flashes would generate a thunder signature similar to or stronger than those of long laboratory sparks and they could also be detected by optical means. As in the case of thunderstorm-assisted macro lightning, these mini-lightning flashes are also associated with straight channels. Moreover, since the frequency of mini-lightning flashes is about thirty times greater than the macro-generated lightning flashes assisted by thunderstorms, they could be used as a means to look for the paths of macroscopic dark matter crossing the atmosphere.
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| 3. |
- Cooray, Vernon, 1952-, et al.
(författare)
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Exact Expressions for Lightning Electromagnetic Fields : Application to the Rusck Field-to-Transmission Line Coupling Model
- 2023
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Ingår i: Atmosphere. - : MDPI. - 2073-4433. ; 14:2
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Tidskriftsartikel (refereegranskat)abstract
- An exact analytical expression for the electric field of the return stroke as excited by a propagating step current source is derived in this paper. This expression could be advantageously used to evaluate the disturbances caused by lightning on overhead lines. There are three equivalent procedures to evaluate the voltages induced by lightning on power lines, namely, the Agrawal-Price-Gurbaxani model, the Taylor-Satterwhite-Harrison model, and the Rachidi model. In the case of a vertical return stroke channel, the coupling model developed by Rusck becomes identical to these three coupling models. Due to its simplicity, the Rusck model is frequently used by engineers to study the effects of lightning on power distribution and transmission lines. In order to reduce the time involved in the electromagnetic field calculation, the Rusck model is incorporated with an analytical expression for the electromagnetic fields of the return stroke excited by a propagating step current pulse. Our research work shows that the Rusck expression can be used to calculate the peak values of lightning induced voltages to an accuracy of about 10%. However, the use of this analytical expression to calculate the time derivatives of lightning induced voltages may result in errors as large as 50%. The derived expression in this paper can be used to correct for this inaccuracy. We also provide an exact expression for the electric field at any given point in space when the propagating current is an impulse function. This expression can be combined with the convolution integral to obtain the electric field corresponding to waveforms similar to measured return stroke currents.
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| 4. |
- Cooray, Vernon, 1952-, et al.
(författare)
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Ionization Waves Enhance the Production of X-rays during Streamer Collisions
- 2021
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Ingår i: Atmosphere. - : MDPI. - 2073-4433. ; 12:9
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Tidskriftsartikel (refereegranskat)abstract
- Experimental data show that in laboratory sparks, X-rays are produced in time synchronization with the meeting of streamers of opposite polarity just before the final breakdown of the discharge gap. It has been suggested that the electric field enhancement created during the collision of streamers could provide the necessary conditions for electron acceleration, even though some of the theoretical studies show that the duration of the electric field is not long enough to do so. The experimental data on laboratory discharges show that. when streamers of opposite polarity meet each other, a potential or ionization wave that renders the streamer channels conducting is initiated. This paper shows that these ionization waves that convert the discharge channels from weakly conducting to highly conducting are associated with electric fields large enough to accelerate electrons to relativistic energies.
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| 5. |
- Cooray, Vernon, 1952-, et al.
(författare)
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Modeling Compact Intracloud Discharge (CID) as a Streamer Burst
- 2020
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Ingår i: Atmosphere. - : MDPI. - 2073-4433. ; 11:5
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Tidskriftsartikel (refereegranskat)abstract
- Narrow Bipolar Pulses are generated by bursts of electrical activity in the cloud and these are referred to as Compact Intracloud Discharges (CID) or Narrow Bipolar Events in the current literature. These discharges usually occur in isolation without much electrical activity before or after the event, but sometimes they are observed to initiate lightning flashes. In this paper, we have studied the features of CIDs assuming that they consist of streamer bursts without any conducting channels. A typical CID may contain about 10(9) streamer heads during the time of its maximum growth. A CID consists of a current front of several nanosecond duration that travels forward with the speed of the streamers. The amplitude of this current front increases initially during the streamer growth and decays subsequently as the streamer burst continues to propagate. Depending on the conductivity of the streamer channels, there could be a low-level current flow behind this current front which transports negative charge towards the streamer origin. The features of the current associated with the CID are very different from those of the radiation field that it generates. The duration of the radiation field of a CID is about 10-20 mu s, whereas the duration of the propagating current pulse associated with the CID is no more than a few nanoseconds in duration. The peak current of a CID is the result of a multitude of small currents associated with a large number of streamers and, if all the forward moving streamer heads are located on a single horizontal plane, the cumulative current that radiates at its peak value could be about 10(8) A. On the other hand, the current associated with an individual streamer is no more than a few hundreds of mA. However, if the location of the forward moving streamer heads are spread in a vertical direction, the peak current can be reduced considerably. Moreover, this large current is spread over an area of several tens to several hundreds of square meters. The study shows that the streamer model of the CID could explain the fine structure of the radiation fields present both in the electric field and electric field time derivative.
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| 6. |
- Cooray, Vernon, 1952-, et al.
(författare)
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On the Apparent Non-Uniqueness of the Electromagnetic Field Components of Return Strokes Revisited
- 2021
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Ingår i: Atmosphere. - : MDPI. - 2073-4433. ; 12:10
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Tidskriftsartikel (refereegranskat)abstract
- Recent research work shows that there are four procedures that can be used to calculate the electromagnetic fields from a current source. These different procedures, even though producing the same total field, give rise to field components that differ from one procedure to another. This has led to the understanding that the various field terms that constitute the total field cannot be uniquely determined. In this paper, it is shown that all four field expressions can be reduced to a single field expression, and the various field terms arising from acceleration, uniformly moving, and stationary charges can be uniquely determined. The differences in the field terms arising from different techniques are caused by the different ways of summing up the contribution to the total electric field coming from the accelerating, moving, and stationary charges.
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| 7. |
- Cooray, Vernon, 1952-, et al.
(författare)
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Polarity Asymmetry in Lightning Return Stroke Speed Caused by the Momentum Associated with Radiation
- 2021
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Ingår i: Atmosphere. - : MDPI. - 2073-4433. ; 12:12
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Tidskriftsartikel (refereegranskat)abstract
- In positive lightning return strokes, the net momentum transported by the radiation field has the same direction as the momentum associated with electrons, whereas the momentum associated with electrons is in opposite direction to the momentum of radiation in negative return strokes. It is shown here that this polarity asymmetry could limit the maximum speed of positive return strokes with respect to the negative return strokes.
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| 8. |
- Cooray, Vernon, 1952-, et al.
(författare)
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The Upper Bound of the Speed of Propagation of Waves along a Transmission Line
- 2020
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Ingår i: Progress In Electromagnetics Research M. - : ELECTROMAGNETICS ACAD. - 1937-8726. ; 93, s. 119-125
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Tidskriftsartikel (refereegranskat)abstract
- According to theory, once certain conditions are fulfilled, current and voltage pulses propagate along ideal transmission lines with the speed of light. One can reach such a conclusion only when the conductors are assumed to be perfectly conducting, which cannot be realized in practice. A wave can only propagate along a transmission line with the speed of light if no energy has to be spent in establishing the current in the conductor. However, in establishing a current in a transmission line, energy has to be supplied to the electrons to set them in motion since they have a mass. The energy transfer to the electrons manifests itself in the form of an inductance which is called the kinetic inductance. The effect of the kinetic inductance has to be taken into account in signal propagation along high carrier mobility conductors including super conductors. In the case of transmission lines, the kinetic inductance leads to a change in the characteristic impedance and a reduction in the speed of propagation of waves along the transmission line. The goal of this paper is to show that the kinetic inductance will set an upper bound to the speed of propagation of waves along transmission lines, which is smaller than the speed of light.
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| 9. |
- Arevalo, Liliana, et al.
(författare)
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Attachment process of the discharge of competing grounded electrodes - Experimental observations and modeling
- 2021
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Ingår i: 2021 35th International Conference on Lightning Protection (ICLP) and XVI International Symposium On Lightning Protection (SIPDA). - : IEEE. - 9781665423465
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Konferensbidrag (refereegranskat)abstract
- The lightning attachment discharge process theory is based on studies of the physics of the discharge obtained from high voltage laboratory tests. The process of propagation of positive and negative discharges has been studied independently and then the gathered information has been used to understand and explain the lightning attachment development. In this paper, an experimental set-up is built to describe the dynamic behavior of positive and negative discharges. Electrodes of different dimensions placed at different distances are used as grounded electrodes and a high voltage electrode is subject to negative switching impulses. Test results allow to identify different stages of the dynamic process of attachment of the discharge between a downward negative discharge and a positive upward leader discharge. The principles of physics of discharge for positive and negative polarities are used to model the laboratory test measurements. The model can reproduce in an accurate manner majority of the dynamic processes of the discharge. In addition, statistical results of the effect of nearby and competing upward discharges is obtained.
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| 10. |
- Baharin, Shamsul Ammar Shamsul, et al.
(författare)
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Electromagnetic Interference From Natural Lightning on 4G Communication Links
- 2024
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Ingår i: IEEE Access. - : Institute of Electrical and Electronics Engineers (IEEE). - 2169-3536. ; 12, s. 14870-14881
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Tidskriftsartikel (refereegranskat)abstract
- In this study, microwave radiation pulses emitted from natural lightning have been found to interfere with the Fourth Generation Long Term Evolution (4G LTE) mobile communication data transmission. Two sets of measurement instruments have been synchronized where lightning electric field sensor together with 4G LTE network were evaluated its performance under two conditions namely fair-weather (four cases) and storm (four lightning cases). The microwave radiation emitted from lightning was directly measured without the use of a mixer and down-convertor to ensure the preservation of information such as the number of pulses and amplitude. A client-server architecture has been set up for data transmission utilizing User Datagram Protocol (UDP) where the packets have been generated by using Internet Performance Working Group Third Version (Iperf3) platform. Under fair-weather conditions, the 4G LTE connection at both the client and server nodes demonstrated stability and experienced minimal impact. On the other hand, natural lightning electromagnetic interference disrupted the 4G LTE communication links. Among the four reported storms, three storms have affected the 4G LTE data transmission. The first and fourth storms resulted in a complete connection drop to zero, lasting for 4 minutes and 2 seconds and for 44 seconds, respectively. The observation of hundreds microwave radiation pulses, each characterized by individual oscillating features suggests a potential disruption to packet transmission. Moreover, negative could-to-ground (-CG) and intra-cloud (IC) lightning flashes have been identified as the primary sources of interference to the 4G LTE data transmission. This information could be useful for future studies and for developers working on improving the reliability and performance of 4G LTE networks, particularly in areas prone to thunderstorms.
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| 11. |
- Baharin, Shamsul Ammar Shamsul, et al.
(författare)
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Microwave and Very High Frequency Radiations of The First Narrow Initial Breakdown
- 2021
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Ingår i: 2021 35TH INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP) AND XVI INTERNATIONAL SYMPOSIUM ON LIGHTNING PROTECTION (SIPDA). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781665423465
-
Konferensbidrag (refereegranskat)abstract
- This paper reports the observation of microwave and very high frequency (VHF) radiation pulses associated with the first narrow (<10us) initial breakdown (IB) pulses of ten negative cloud-to-ground (-CG) flashes. The centre frequency of microwave and VHF sensors was 0.97 GHz and 60 MHz, respectively. We found that all microwave pulses were the initiation event led the first VHF pulses ranging between 0.03187 and 2.57968 mu s and led the first narrow IB pulses ranging between 0.02382 and 2.70202 mu s. Half of the VHF pulses were observed to lead the first narrow IB pulses ranging between 0.03453 and 0.128 mu s. Moreover, polarity of microwave radiation pulses was always positive while the polarity of the first narrow IB pulses always negative. On the other hand, half of VHF radiation pulses had the same polarity as microwave radiation pulses.
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| 12. |
- Baharin, Shamsul Ammar Shamsul, et al.
(författare)
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Microwave radiation associated with positive narrow bipolar events
- 2023
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Ingår i: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier. - 1364-6826 .- 1879-1824. ; 242
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we examined seven isolated positive Narrow Bipolar Events (NBEs), one positive NBE that initiated an IC flash progressed to a single-stroke Cloud-to-Ground (CG) flash, and one positive NBE that initiated an IC flash. Seven NBEs have been accompanied by significant Very-High Frequency (VHF) and microwave radiation pulses. We recorded all NBEs from two measurement stations (ST1 and ST2) separated at 13.3 km apart which consisted of fast antenna (FA) and slow antenna (SA) sensors, a magnetic field (B-field) sensor, a VHF sensor (60 MHz), and a microwave sensor (0.97 GHz). The waveforms were sampled at 2.5 GHz (400 ps). The key finding is that all microwave radiation pulses have been found to precede both the VHF radiation pulses and NBEs with average lead time of 63 +/- 39 ns and 122 +/- 143 ns, respectively. In comparison to stepped leader pulses or SLPs (conventional breakdown), the average lead time of microwave to VHF for NBEs (fast breakdown) was 88% faster compared to the average lead time of microwave to VHF for SLPs. Moreover, the average lead time of VHF to NBEs was 56% faster when compared to the average lead time of VHF to SLPs. The VHF interferometer map for an isolated NBE (NBE6) showed upward propagation of VHF radiation sources (fast negative breakdown) with initiation altitude, total length of the VHF radiation sources propagation, and estimated velocity were 10.2 +/- 0.3 km, 2.9 +/- 0.6 km, and 1.8 x 108 and 2.8 x 108 ms-1, respectively. On the other hand, interferometer map for an NBE that initiated a single-stroke CG (NBE3) showed bidirectional fast streamers propagation with initiation altitude, total length of the VHF radiation sources propagation, and estimated velocity were 14.0 +/- 0.4 km, 2.9 +/- 0.82 km, and 1.6 x 108 and 2.8 x 108 ms-1, respectively. Clearly, the microwave and VHF radiation pulses associated with positive NBEs have been emitted by different processes of fast breakdown mechanism. Therefore, it can be suggested that the microwave radiation is emitted by electron avalanches/corona while the VHF ra-diation is emitted by fast propagating streamers.
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| 13. |
- Baharin, Shamsul Ammar Shamsul, et al.
(författare)
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Microwave radiation associated with stepped leaders of negative cloud-to-ground flashes
- 2022
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Ingår i: Atmospheric research. - : Elsevier. - 0169-8095 .- 1873-2895. ; 270
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, Very-High Frequency (VHF) and microwave radiation pulses associated with stepped leader pulses (conventional breakdown) are examined. A total of 100 stepped leader pulses (SLPs) with the associated 100 quiet periods (QPs) from ten negative cloud-to-ground (CG) flashes within the reversal distance (<8 km) have been analyzed. The QP is defined as the period between two SLPs when no electrical activity within the fast antenna sensor bandwidth was detected. The measurement system is made up of fast antenna (FA) and slow antenna (SA) sensors, a VHF sensor (60 MHz center frequency with 40 MHz bandwidth), and a microwave sensor (0.97 GHz center frequency with 20 MHz bandwidth). The waveforms were sampled at 2.5 GHz (400 ps). The total durations of the SLPs and QPs were 2.648 +/- 1.152 mu s and 2.708 +/- 1.670 mu s, respectively. All microwave and VHF radiation waveforms have been detected as clear individual oscillating pulses. The key finding is that the microwave radiation can be classified into three categories based on the total number of detected individual oscillating pulses during the QP. Two microwave pulses detected during the QP (Category 1) are suggested to be associated with the electron avalanche/corona process at the tip of an existing negative leader and a space stem. The VHF pulses associated with the microwave pulses are suggested to be emitted by propagating streamers. On the other hand, a single microwave pulse detected during the QP (Category 2) is suggested to be emitted by the electron avalanche/corona process of a space stem. The VHF pulses associated with the microwave pulse are suggested to be emitted by propagating streamers. In both categories, 70% of the microwave radiation pulses have been observed to precede VHF radiation pulses with an average lead time of 0.848 +/- 1.336 mu s. The head-on collision of a downward propagating negative streamer and an upward propagating positive streamer (from space stem) emitted significant microwave radiation. A new negative leader was formed when the head-on collision took place. The microwave radiation pulses emitted by the head-on collision process were observed to precede SLPs with an average lead time of 0.423 +/- 0.378 mu s. Around 80% of the microwave radiation pulses preceded VHF radiation pulses with average lead time of 0.540 +/- 0.596 mu s. Therefore, microwave and VHF radiation pulses are suggested to be emitted by different processes of the electrical breakdown mechanism. The microwave radiation is emitted by electron avalanche/corona/head-on collision while the VHF radiation is emitted by propagating streamers.
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| 14. |
- Baharin, Shamsul Ammar Shamsul, et al.
(författare)
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Very high frequency radiation emitted by negative narrow bipolar events occurred over malacca strait
- 2024
-
Ingår i: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier. - 1364-6826 .- 1879-1824. ; 259
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, Very -High Frequency (VHF) radiation pulses associated with 11 negative Narrow Bipolar Events (NBEs) produced by a tropical storm over Malacca Strait are examined. The lightning data were recorded from a measurement station (ST) which consisted of a fast antenna (FA) and three VHF sensors (two 5 m perpendicular baselines interferometer). The average rise time (RT), average zero -crossing time (ZCT), average pulse duration (PD), and range of peak currents of the negative NBEs were 1.4 +/- 0.4 mu s, 2.7 +/- 1.0 mu s, 12.0 +/- 6.9 mu s, and -10 to -64 kA, respectively. The key finding is that all VHF radiation pulses have been found to precede the negative NBEs with an average lead time of 0.7 +/- 0.3 mu s. An interferometer map for one negative NBE (labelled as NBE10) detected at 35.7 km from ST has shown a characteristic of mixed propagation direction of fast streamers. The first VHF radiation source was detected at 12.4 +/- 0.4 km above sea level. The total length and estimated velocity of the main propagation of the VHF radiation sources were 2.2 +/- 0.7 km and between 1.4 x 10 8 and 2.8 x 10 8 ms -1 , respectively. Moreover, based on the Himawari satellite image, the maximum extent of the cloud top height was estimated to be around 20.9 km over sea level (over Malacca Strait). All the VHF radiation sources associated with NBE10 were suggested to be detected above the main negative charge region (6 km altitude that corresponds to -10 degrees C). Thus, it could be suggested that NBE10 was initiated most likely in the environment of the ice crystals alone, based on the first altitude of the VHF radiation source and maximum extent of cloud top height.
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| 15. |
- Chandimal, Lasantha, et al.
(författare)
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A field study on the energy dissipation associated with step and touch voltage in earthing systems encased in earth enhancing compounds
- 2024
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Ingår i: Electric power systems research. - : Elsevier. - 0378-7796 .- 1873-2046. ; 231
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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.
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| 16. |
- Cooray, Vernon, 1952-, et al.
(författare)
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A Self-Consistent Return Stroke Model That Includes the Effect of the Ground Conductivity at the Strike Point
- 2022
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Ingår i: Atmosphere. - : MDPI AG. - 2073-4433. ; 13:4
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Tidskriftsartikel (refereegranskat)abstract
- A current generation type return stroke model which can take into account the possible modifications of the return stroke properties by the soil conductivity at the strike point of the lightning flash is introduced. The model is also capable of incorporating the reflection of the current at the ground end of the return stroke channel. In this paper, this return stroke model is used to investigate (a) the effect of the ground conductivity at the strike point on the source electromagnetic fields generated by return strokes and (b) the effect of current reflection at ground level on the electromagnetic field generated by return strokes. The source electromagnetic fields are the electromagnetic fields generated by lightning flashes calculated in such a way that they are not distorted by propagation effects. The results obtained show that the ground conductivity at the strike point does not significantly influence the return stroke current peak or the radiation field peak for ground conductivities higher than about 0.001 S/m. However, strike points with very poor conductivities (lower than 0.001 S/m) would result in a decrease of the peak electric field. In contrast to the peak values of the lightning current and the electric field, the peak values of the time derivatives of the lightning current and electric field are significantly reduced when the strike point of the lightning flash is located over a finitely conducting ground. The inclusion of the current reflection at ground level influences significantly the saturation of the close electric fields. The current reflection also gives rise to residual electric fields, a difference in the field levels generated by the dart leader and the return stroke. The residual field decreases as the fraction of the reflected current decreases.
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| 17. |
- Cooray, Vernon, 1952-, et al.
(författare)
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Current propagation type self-consistent leader-return stroke model
- 2023
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Ingår i: Electric power systems research. - : Elsevier. - 0378-7796 .- 1873-2046. ; 217
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Tidskriftsartikel (refereegranskat)abstract
- A current propagation type return stroke model which is consistent with the estimated distribution of the charge on the leader channel is described. The model takes into account the dispersion of the return stroke current along the return stroke channel. The model is capable of generating lightning return stroke electromagnetic fields that are in close agreement with experimental observations. The model could also be used to estimate the electric fields from the leader-return stroke combination at any given distance.
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| 18. |
- Cooray, Vernon, 1952-, et al.
(författare)
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Field-to-Transmission Line Coupling Models With Special Attention to the Cooray-Rubinstein Approximation
- 2021
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Ingår i: IEEE transactions on electromagnetic compatibility (Print). - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9375 .- 1558-187X. ; 63:2, s. 484-493
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Tidskriftsartikel (refereegranskat)abstract
- There are three equivalent procedures to evaluate the voltages induced by lightning on power lines, namely, the Agrawal-Price-Gurbaxani model, the Taylor-Satterwhite-Harrison model, and the Rachidi model. The Cooray-Rubinstein approximation is a procedure used by scientists and engineers to estimate the horizontal electric field from the lightning that is used in the induced voltage calculations for lines located over a finitely conducting ground. The Cooray-Rubinstein approximation is usually incorporated in calculating the induced overvoltages using the Agrawal-Price-Gurbaxani model. In this article, it is shown how this approximation could be incorporated into the other two coupling models. The resulting coupling equations are compared to each other by calculating the voltages induced on two idealized overhead transmission lines.
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| 19. |
- Cooray, Vernon, 1952-, et al.
(författare)
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Latitude and Topographical Dependence of Lightning Return Stroke Peak Current in Natural and Tower-Initiated Negative Ground Flashes
- 2020
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Ingår i: Atmosphere. - : MDPI. - 2073-4433. ; 11:6
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Tidskriftsartikel (refereegranskat)abstract
- Experimental data show that the peak currents of first and subsequent lightning return strokes in negative ground flashes increase with decreasing latitude. In this paper, the reason for this dependence of peak return stroke current on latitude is explained using the fact that the height of the charge centers increases with decreasing latitude. Results show that in tropical regions where the height to the negative charge center is about 8 km, the median values of the first and the subsequent return stroke peak currents are about 42 kA and 15 kA, respectively. If the height to the charge center is larger than 8 km, the peak currents will also become larger. For example, if the location of the charge center is increased to about 9 km, the median values of the first and subsequent return stroke peak currents will increase to about 45 kA and 16 kA respectively. The same reasoning shows that, even in the same geographical region, the peak return stroke current may decrease as the elevation of the ground where the lightning strikes take place increases. The results also indicate that the peak subsequent return stroke current in tower-initiated negative lightning flashes decreases as the height of the tower increases. These theoretical predictions are in general agreement with the available experimental data.
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| 20. |
- Cooray, Vernon, 1952-, et al.
(författare)
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Modified Transmission Line Model with a Current Attenuation Function Derived from the Lightning Radiation Field-MTLD Model
- 2021
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Ingår i: Atmosphere. - : MDPI. - 2073-4433. ; 12:2
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Tidskriftsartikel (refereegranskat)abstract
- In return strokes, the parameters that can be measured are the channel base current and the return stroke speed. For this reason, many return stroke models have been developed with these two parameters, among others, as inputs. Here, we concentrate on the current propagation type engineering return stroke models where the return stroke is represented by a current pulse propagating upwards along the leader channel. In the current propagation type return stroke models, in addition to the channel base current and the return stroke speed, the way in which the return stroke current attenuates along the return stroke channel is specified as an input parameter. The goal of this paper is to show that, within the confines of current propagation type models, once the channel base current and the return stroke speed are known, the measured radiation field can be used to evaluate how the return stroke current attenuates along the channel. After giving the mathematics necessary for this inverse transformation, the procedure is illustrated by extracting the current attenuation curve from the typical wave shape of the return stroke current and from the distant radiation field of subsequent return strokes. The derived attenuation curve is used to evaluate both the subsequent and first return stroke electromagnetic fields at different distances. It is shown that all the experimentally observed features can be reproduced by the derived attenuation curve, except for the subsidiary peak and long zero-crossing times. In order to obtain electromagnetic fields of subsequent return strokes that are in agreement with measurements, one has to incorporate the current dispersion into the model. In the case of first return strokes, both current dispersion and reduction in return stroke speed with height are needed to obtain the desired features.
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| 21. |
- Cooray, Vernon, 1952-, et al.
(författare)
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The Energy, Momentum, and Peak Power Radiated by Negative Lightning Return Strokes
- 2020
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Ingår i: Atmosphere. - : MDPI AG. - 2073-4433. ; 11:12
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Tidskriftsartikel (refereegranskat)abstract
- Electromagnetic radiation fields generated by return strokes transport both energy and momentum from the return stroke to outer space. The momentum transported by the radiation field has only a vertical or z component due to azimuthal symmetry (cylindrical symmetry) associated with a vertical return stroke. In this paper, the energy, momentum, and peak power radiated by return strokes as a function of the return stroke current, return stroke speed, and the zero-crossing time of the radiation fields are studied. The results obtained by numerical simulations for the energy, vertical momentum, and the peak power radiated by lightning return strokes (all parameters normalized by dividing them by the square of the radiation field peak at 100 km) are the following: A typical first return stroke generating a radiation field having a 50 μs zero-crossing time will dissipate field normalized energy of about (1.7–2.5) × 103 J/(V/m)2 and field-normalized vertical momentum of approximately (2.3–3.1) × 10−6 Kg m/s/(V/m)2. A radiation field with a zero-crossing time of 70 μs will dissipate about (2.6–3.4) × 103 J/(V/m)2 in field-normalized energy and (3.2–4.3) × 10−6 Kg m/s/(V/m)2 in field-normalized vertical momentum. The results show that, for a given peak radiation field, the radiated energy and momentum increase with increasing zero-crossing time of the radiation field. The normalized peak power generated by a first return stroke radiation field is about 1.2 × 108 W/(V/m)2 and the peak power is generated within about 5–6 μs from the beginning of the return stroke. Conversely, a typical subsequent return stroke generating a radiation field having a 40 μs zero-crossing time will dissipate field-normalized energy of about (6–9) × 102 J/(V/m)2 and field-normalized vertical momentum of approximately (7.5–11) × 10−7 Kg m/s/(V/m)2. The field-normalized peak power generated by a subsequent return stroke radiation field is about 1.26 × 108 W/(V/m)2 and the peak power is generated within about 0.7–0.8 μs from the beginning of the return stroke. In addition to these parameters, the possible upper bounds for the energy and momentum radiated by return strokes are also presented.
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| 22. |
- Cooray, Vernon, 1952-, et al.
(författare)
-
The Geometry and Charge of the Streamer Bursts Generated by Lightning Rods under the Influence of High Electric Fields
- 2022
-
Ingår i: Atmosphere. - : MDPI. - 2073-4433. ; 13:12
-
Tidskriftsartikel (refereegranskat)abstract
- The streamer bursts generated during the initiation and propagation of leaders play an important role in the creation and maintenance of hot discharge channels in air. The most important parameters related to streamer bursts in this respect are the length of the streamer bursts, their lateral extent and the charge associated with them. The lateral extent of the streamer bursts may play a significant role in deciding the path and the tortuosity of the discharge channels of laboratory discharges and lightning. The charges associated with the streamer bursts are needed in understanding the physical processes associated with the streamer-to-leader transition. In this paper, the length, the lateral extension and the charge of the streamer regions generated by grounded conductors when exposed to external electric fields are estimated. This estimation is based on two assumptions: (i) once a streamer is incepted, the streamer head follows the direction of maximum background electric field at the location of the streamer head and (ii) the streamer continues to extend along this direction until the potential drop along the streamer channel matches the potential drop caused by the background electric field between the initial and end points of the streamer channel. The same technique could be used to estimate the streamer bursts generated in laboratory discharges and lightning stepped leaders. It is shown that in estimating the geometry of the streamer region, it is necessary to include the spread of streamers caused by branching. Moreover, the charge associated with the streamer region increases as the frequency of branching increases. The results obtained confirm that the charge in the streamer region can significantly change the potential ahead of the streamer region from the background potential and this has to be taken into account in any study that simulates the initiation and propagation of lightning leaders. Since the streamer bursts of leaders control the direction and speed of the leaders, the technique we have used here could be implemented in lightning leader progression models.
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| 23. |
- Cooray, Vernon, 1952-
(författare)
-
Unification of engineering return stroke models
- 2021
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Ingår i: Electric power systems research. - : Elsevier. - 0378-7796 .- 1873-2046. ; 195
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Tidskriftsartikel (refereegranskat)abstract
- Engineering models burrow various features from transmission line theory and combine them using empirical data to create models that can predict the electromagnetic fields of lightning return strokes in space and time. At present, engineering models are the most successful in predicting the features of lightning electromagnetic fields in close agreement with the experimental data. Today, most scientists who are interested in lightning protection use engineering models in their studies. A large number of engineering return stroke models exist in the literature. Depending on the assumptions made they can be categorized as Current Propagation models (CP-models), Current Generation models (CG-models) and Current Dissipation models (CD-models). The goal of this paper is to describe the different approximations used in constructing these engineering return stroke models and to show that all these models are a special case of a more general model which we call Current model (C-model). We will show how various return stroke models can be precipitated from the C-model by neglecting different features associated with it.
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| 24. |
- Frost, Anna E., 1988-, et al.
(författare)
-
Do pre-recorded lessons in combination with formative assessments fulfil the learning necessity of engineering students?
- 2022
-
Ingår i: Bidrag från 8:e Utvecklingskonferensen för Sveriges ingenjörsutbildningar. - : Karlstads universitet. - 9789178672813 ; , s. 21-25
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- As an effort to increase digitization of education during the ongoing pandemic in Spring 2021, the course ”Electromagnetism II with electric circuits” at Uppsala University has been conducted in a blended form with both pre-recorded sessions and live online sessions. About half of the lectures were live sessions, and the rest were pre-recorded. Among the lessons, more than 75 % were pre-recorded. When the teaching is pre-recorded, the teachers do not get reactions directly from the students, either verbally or from facial expressions. Therefore,self-correcting quizzes were implemented for every lecture, and short formative evaluations were implemented for every lesson. The main objective was to increase the number of students participating in the lessons, which hopefully would lead to more students passing the course. More students watched the pre-recorded lessons than attended the lessons on campus previous years on the course. More students passed the exam on the course compared to previous years, but it cannot be excluded that this is partially or completely due to the exam being different due to the pandemic. The short formative evaluations had at least seven respondents during the first four lessons, but from lesson five and onward, the number of respondents was two or fewer. The quizzes which most students attempted were right after or right before the pre-exams (”duggor” in Swedish), but otherwise relatively few students answered the quizzes. When asked in the course evaluation, it varied a lot whether the students liked, disliked, or were neutral to have pre-recorded lessons, with slightly more students saying they preferred live sessions.
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| 25. |
- Guo, Jun, et al.
(författare)
-
Investigation of Electromagnetic Field Coupling to a Transmission Line Terminated with Non-Vertical Risers
- 2020
-
Ingår i: 2020 XXXIIIRD General Assembly And Scientific Symposium Of The International Union Of Radio Science. - : IEEE.
-
Konferensbidrag (refereegranskat)abstract
- Recently, a simple and efficient method was proposed to take into account non-vertical risers at the end of transmission lines through an equivalent partial inductance. This paper evaluates the frequency above which the inductance needs to be taken into account. In addition, the proposed method is validated in the time domain.
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| 26. |
- Guo, Jun, et al.
(författare)
-
Lightning-Induced Voltage on an Overhead Transmission Line Terminated with Non-veritical Risers
- 2021
-
Ingår i: 2021 35TH INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP) AND XVI INTERNATIONAL SYMPOSIUM ON LIGHTNING PROTECTION (SIPDA). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781665423465
-
Konferensbidrag (refereegranskat)abstract
- T Recently, a simple and efficient method was proposed to take into account non-vertical risers for transmission lines excited by external fields. In this paper, the proposed method is used to investigate the effect of non-vertical risers on lightning-induced voltages.
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| 27. |
- Houard, Aurélien, et al.
(författare)
-
Laser-guided lightning
- 2023
-
Ingår i: Nature Photonics. - : Springer Nature. - 1749-4885 .- 1749-4893. ; 17:3, s. 231-235
-
Tidskriftsartikel (refereegranskat)abstract
- Lightning discharges between charged clouds and the Earth's surface are responsible for considerable damages and casualties. It is therefore important to develop better protection methods in addition to the traditional Franklin rod. Here we present the first demonstration that laser-induced filaments-formed in the sky by short and intense laser pulses-can guide lightning discharges over considerable distances. We believe that this experimental breakthrough will lead to progress in lightning protection and lightning physics. An experimental campaign was conducted on the Santis mountain in north-eastern Switzerland during the summer of 2021 with a high-repetition-rate terawatt laser. The guiding of an upward negative lightning leader over a distance of 50 m was recorded by two separate high-speed cameras. The guiding of negative lightning leaders by laser filaments was corroborated in three other instances by very-high-frequency interferometric measurements, and the number of X-ray bursts detected during guided lightning events greatly increased. Although this research field has been very active for more than 20 years, this is the first field-result that experimentally demonstrates lightning guided by lasers. This work paves the way for new atmospheric applications of ultrashort lasers and represents an important step forward in the development of a laser based lightning protection for airports, launchpads or large infrastructures. A terawatt laser filament is shown to be able to guide lightning over a distance of 50 m in field trials on the Santis mountain in the Swiss Alps.
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| 28. |
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| 29. |
- Kereszy, Istvan, et al.
(författare)
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Energetic Radiation from Subsequent-Stroke Leaders : The Role of Reduced Air Density in Decayed Lightning Channels
- 2022
-
Ingår i: Applied Sciences. - : MDPI AG. - 2076-3417. ; 12:15
-
Tidskriftsartikel (refereegranskat)abstract
- Featured Application Electric fields produced by lightning subsequent stroke leaders are sufficiently high for acceleration of electrons to relativistic speeds, leading to generation of X-rays/gamma-rays as a result of Bremsstrahlung emissions. Leaders of subsequent strokes in negative cloud-to-ground lightning are known to produce X-ray/gamma-ray emissions detectable at distances of a few kilometers or less from the lightning channel. These leaders usually develop in decayed but still warm channels of preceding strokes. We computed electric field waveforms at different points along the path of subsequent leader as those points are traversed by the leader tip. For a typical subsequent leader, the electric field peak is a few MV/m, which is sufficient for production of energetic radiation in a warm (reduced air density) channel. We examined the dependence of electric field peak on the leader model input parameters, including the prospective return-stroke peak current (a proxy for the leader tip potential) and leader propagation speed, and compared model predictions with measurements.
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| 30. |
- Mohammad, S. A., et al.
(författare)
-
Azimuth and elevation factors correction for single station lightning electromagnetic field sensor
- 2021
-
Ingår i: Geografia. - : Penerbit Universiti Kebangsaan Malaysia (UKM Press). - 2180-2491. ; 17:4, s. 378-392
-
Tidskriftsartikel (refereegranskat)abstract
- This study aims to find the location of lightning return strokes using a single station electromagnetic field sensor with the implementation of magnetic field Factor B correction to best match with a reliable lightning strike location reference from TNB Research (TNBR) that uses Vaisala lightning detector with +/- 500m tolerance. A parallel plate antenna was used to measure the electric fields while two orthogonal loop antennas were used to measure the magnetic fields from thunderstorms in Melaka. Based on the type of Cloud-to-Ground flash and its recorded magnetic field peak amplitude polarities, the general direction of the lightning source could be determined in four quadrants divided equally between the cardinal directions. Measurement of return stroke peak amplitudes from electromagnetic field waveforms, distance between lightning measurement station and lightning strike was determined. Factor B corrections varied between 53M to 69M where the separation distance between compared strikes averaged 3.22 km. From the varied Factor B, it was averaged to 60.1M that yield a separation distance between the same compared strikes between 0.75 to 15.02 km. From all the strikes compared, the average separation distance between compared strikes was 7.64 km. It was determined that the accuracy of our lightning measurement system lightning location were between 7.14 and 8.14 km.
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| 31. |
- Mohammad, Sulaiman Ali, et al.
(författare)
-
Characteristics of Lightning Electromagnetic Fields Produced by Antarctica Storms
- 2022
-
Ingår i: Atmosphere. - : MDPI AG. - 2073-4433. ; 13:4
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents the temporal characteristics of electromagnetic fields produced by cloud-to-ground (CG) lightning flashes associated with Antarctica storms. A total of 51 positive CG (+CG) and 103 negative CG (-CG) flashes have been recorded by a magnetic direction finder (MDF) sensor in King Sejong Station, King George Island. In total, 47 positive and 107 negative return strokes were located, ranges from 32 to 569 km. All CG flashes were detected to occur over the ocean. The return strokes characteristics include the observations of slow front, fast rising, rise time, and pulse duration with geometric mean values of 3.2, 0.53, 3.21, 13.12, and 67.09 mu s for +CG flashes, while 3.9, 0.57, 3.72, 20.75, and 69.86 mu s for -CG flashes, respectively. Additionally, the average peak currents of +CG and -CG flashes were 4.13 kA and 3.14 kA, respectively. The temporal characteristics of the return strokes of Antarctica storms are comparable to other geographical regions. The smaller peak currents might be due to small magnitude of Antarctica cloud charges when compared to other geographical regions.
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| 32. |
- Mohammad, Sulaiman Ali, et al.
(författare)
-
Observation of Lightning Occurrence Surrounding Antarctica Peninsula
- 2021
-
Ingår i: 2021 35TH INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP) AND XVI INTERNATIONAL SYMPOSIUM ON LIGHTNING PROTECTION (SIPDA). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781665423465
-
Konferensbidrag (refereegranskat)abstract
- In this study, we present the observation of cloud-to-ground (CG) flashes detected surrounding Antarctica Peninsula. Lightning sensors had been setup and deployed at King Sejong station in King George Island, Antarctica Peninsula. The lightning sensors consist of fast and slow electric field sensors that uses parallel plate antenna accompanied with respective buffer circuits. A magnetic field sensor was also deployed with two orthogonal loops antennas. The lightning data were collected between 11th and 31st January 2020. 20 storms have been identified with a total of 176 CG flashes detected. From the total CG, 116 were identified as negative CG flashes while 60 were identified as positive CG flashes.
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| 33. |
- Sabri, Muhammad Haziq Mohammad, et al.
(författare)
-
A study of cloud-to-ground lightning flashes initiated by fast positive breakdown
- 2022
-
Ingår i: Atmospheric research. - : Elsevier. - 0169-8095 .- 1873-2895. ; 276
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, we examine the initiation event of two tropical negative cloud to ground (CG) lightning flashes within reversal distance (<8 km) detected on 12 (CG1) and 24 (CG2) November 2019, respectively. The CG flashes were recorded using a fast antenna (FA), slow antenna (SA), magnetic field (B-field), and very high frequency (VHF) sensors located at two observation stations (ST1 and ST2) 13.26 km apart. The key finding is that CG1 flash was initiated by a short VHF pulse followed by a VHF burst (fast positive breakdown) while CG2 flash was initiated by a VHF burst (fast positive breakdown) not preceded by a short VHF pulse. The VHF burst was a precursor for initiation of a narrow bipolar event (NBE)-like pulse and initial electric field changes (IECs). Based on the VHF interferometer map, the VHF sources of NBE-like pulses have been propagated upward predominantly vertical. The initiation altitude, total length of the VHF sources propagation, estimated velocity of NBE-like pulse for CG1 flash were 4.5 +/- 0.5 km, 1.9-3.8 km, and 2.4 x 108 to 4.8 x 108 ms-1, respectively, and for CG2 flash were 5.1 +/- 0.8 km, 0.2-3.0 km, and 2.7 x 107 to 4.1 x 108 ms-1, respectively. It is evident that IECs process has been initiated during fast positive streamers propagation. It can be suggested that the IECs process resulted from charge transfer during a fast positive breakdown. The durations and magnitudes of IECs for CG1 flash were 248.5 mu s and 27.97 V/m, respectively, and for CG2 flash were 265.8 mu s and 2.31 V/m, respectively.
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| 34. |
- Sabri, Muhammad Haziq Mohammad, et al.
(författare)
-
Microwave Radiation Associated with Lightning Initiation Events of Negative Cloud-to-Ground Flashes
- 2022
-
Ingår i: Atmosphere. - : MDPI. - 2073-4433. ; 13:9
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, we examined the initiation events of ten negative cloud-to-ground (CG) flashes detected close to measurement stations on 12 November (CG-1 to CG-5) and 24 November (CG-6 to CG-10), 2019. All CG flashes were accompanied by microwave and very-high frequency (VHF) radiation pulses. We recorded all the CG flashes from two measurement stations (ST1 and ST2), which are separated by 13.3 km and consist of fast and slow antenna (FA and SA) sensors, a magnetic field (B-field) sensor, a VHF sensor (60 MHz), and a microwave sensor (similar to 1 GHz). The key finding is that all of the microwave radiation pulses detected before the onset of initial electric field changes (IECs) preceded all VHF radiation pulses with an average lead time of 1.53 mu s, ranging between 0.3 and 3.0 mu s (for all CG flashes within reversal distance). A total of 50%, 17%, and 33% CG flashes were initiated by a single radiation pulse, two radiation pulses, and three radiation pulses, respectively, and were followed by IECs. Some VHF pulses are classified as short VHF radiation pulses (pulse duration less than 0.5 mu s). The average duration from the first microwave and VHF pulses to the onset of IECs were 53.4 mu s and 32.78 mu s, respectively. The VHF radiation pulses detected before the IECs are suggested to be emitted by short-length positive streamers. Because the microwave radiation pulses were detected earlier (average lead time of 1.53 mu s) than VHF radiation pulses, it is most likely that the microwave pulses were emitted by an electron avalanche process.
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| 35. |
- Sabri, Muhammad Haziq Mohammad, et al.
(författare)
-
Observation of tropical positive cloud-to-ground flashes accompanied by chaotic and regular pulse trains
- 2024
-
Ingår i: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier. - 1364-6826 .- 1879-1824. ; 261
-
Tidskriftsartikel (refereegranskat)abstract
- This study investigates the occurrence of chaotic pulse trains (CPTs) and regular pulse trains (RPTs) in tropical positive cloud-to-ground (CG) lightning flashes. These flashes are categorized into four types based on the initial polarity of the initial breakdown (IB) pulses and their relationship to the first return stroke (RS). A total of 71 positive CG flashes from five thunderstorm events were analyzed. The analysis reveals instances of CPTs and RPTs both before and after the first positive RS, along with the occurrence of mixed polarities in RPTs. Variations in IB pulse polarities and the presence of CPTs and RPTs before the first positive RS were observed, contrasting with previous findings in negative CG flashes. All positive CG flashes have been detected when cloud top height occurrences were between 12 and 18 km. In contrast, for negative CG flashes with CPTs and RPTs the cloud top height occurrences were between 5 and 12 km. It is interesting that CPTs and RPTs can be detected during IB process of positive CG flashes at relatively high altitude in the thundercloud. Perhaps due to low pressure at higher altitudes in the cloud, electrical process associated with CPTs and RPTs are easily discharged before the occurrence first positive return stroke. The altitudes of cloud top heights for the inverse polarity of IB pulses were located between 16 and 18 km. This research enhances the understanding of positive CG lightning initiation process and their relationship with CPTs and RPTs, as well as the occurrence of recoil leaders.
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| 36. |
- Sabri, Muhammad Haziq Mohammad, et al.
(författare)
-
Temporal characteristics of positive cloud-to-ground flashes from tropical thunderstorms
- 2024
-
Ingår i: Atmospheric research. - : Elsevier. - 0169-8095 .- 1873-2895. ; 309
-
Tidskriftsartikel (refereegranskat)abstract
- The occurrence of positive cloud-to-ground (CG) lightning flashes proves to be a challenging task when compared to the negative CG flash which common happen in tropical region. This due to the positively charged clouds to reach higher altitudes to enable the transfer of electrical charges to the Earth's surface. With several sensors that deployed in the Malacca region (2.314077 degrees N, 102.318282 degrees E) such as the wide band fast and slow antenna, magnetic field sensors, and the electric field mill (EFM-100). This research study focuses on the temporal characteristics of positive CG lightning activity in the tropical region during September and October 2021. A total of 203 positive cloud-to-ground flashes were meticulously analyzed in the context of 16 thunderstorm events. Key findings highlight the consistent initiation of positive cloud-to-ground flashes through initial breakdown (IB) pulses, followed by the development of stepped leaders and subsequent return strokes. Notably, most positive cloud-to-ground events (72%) were observed as single strokes and the maximum multiplicity recorded being four subsequent return strokes. Furthermore, the analysis focuses into the temporal aspects of these lightning events, revealing average durations for various parameters, including rise-time (6.26 mu s), zero-crossing (26.43 mu s), pulse duration of the first RS (139.76 mu s), and the interval from the first IB to the first return stroke (134.19 ms). Additionally, the recorded data from the Electric Field Mill (EFM) instruments together with Constant Altitude Plan Position Indicator (CAPPI) radar demonstrate a notable correlation. Specifically, the electric field (E-field) values exhibit a discernible increase when positive cloud-to-ground lightning events are detected near the lightning sensor.
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| 37. |
- Sabri, Muhammad Haziq Mohammad, et al.
(författare)
-
Very High Frequency and Microwave Radiation Associated with Initial Breakdown Process in CG Lightning Flashes from Tropical Storms
- 2021
-
Ingår i: 2021 35TH INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP) AND XVI INTERNATIONAL SYMPOSIUM ON LIGHTNING PROTECTION (SIPDA). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781665423465
-
Konferensbidrag (refereegranskat)abstract
- We present the observation of VHF and microwave radiation pulses associated with initial breakdown process of five negative cloud-to-ground (-CG) flashes from two tropical storms. The -CG flashes were detected within and beyond reversal distances with the locations of the first return stroke were less than 10 km. Out of five flashes, only one detected with initial electric field change (IEC) process. Both VHF and microwave pulses were detected before the first classic IB pulse and the first microwave pulses were found to lead the first VHF pulses ranging between 0.03 and 23.9 mu s.
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| 38. |
- Sapumanage, N., et al.
(författare)
-
Comparison of energy presence in IEC and real transient impulses
- 2021
-
Ingår i: 2021 35TH INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP) AND XVI INTERNATIONAL SYMPOSIUM ON LIGHTNING PROTECTION (SIPDA). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781665423465
-
Konferensbidrag (refereegranskat)abstract
- This study disclosed that the IEC impulse is not an appropriate candidate to benchmark real transient over-voltages owing to have many discrepancies between them in terms of energy localization and frequencies that host such energies. However, the total energy content of the comparable IEC impulse is higher than the real transient voltages. Thus, once tested and passed the endurance at laboratories such an energy absorbing device would not fail at the field applications against single real transient voltage. However the same cannot be guaranteed against the swarm of impulses as the same cannot be tested at the test bench due to many practical constraints. The study revealed that IEC impulses can accommodate only 2.31% of the total energy until it reaches to 90% of the peak voltage, whereas the selected real transient impulses have shown that they could accommodate nearly 6% to 18% of the total incident energy before they reach to 90 % of the peak voltage. Moreover, when IEC impulse reaches to the peak, it can incident only a 9.71% of the total energy, but real transient voltages demonstrated that they have a capacity to incident nearly 30% to 45 % total energy embedded in the impulse.
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| 39. |
- Sapumanage, N., et al.
(författare)
-
Map SPD clamping voltages on to spectral clusters generated by Wavelet transformation
- 2021
-
Ingår i: 2021 35TH INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP) AND XVI INTERNATIONAL SYMPOSIUM ON LIGHTNING PROTECTION (SIPDA). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781665423465
-
Konferensbidrag (refereegranskat)abstract
- This study employed wavelet transformation to disclose the spectrograms of IEC standard impulses and real transient voltages generated by the cloud to ground discharges. The spectral details of each impulse were subdivided into different spectral clusters and the outcome was mapped into respective voltage levels and time to develop correlations. Eventually different protection voltage levels of commercially available surge protection devices (SPDs) and the voltage levels of different spectral clusters were compared to determine whether harmful energy infringements could be possible when the spectral clusters are wrapped by SPDs. This study revealed that all IEC impulses have identical spectral clusters whereas real transient voltages demonstrated that they are inherited with much random spectral distributions. Thus, planning for foolproof through benchmarking real transient impulses against IEC impulses would not produce guaranteed outcomes. Hence, a poor selection of clamping voltages may create a permanent window to infringing a small quantum of harmful energy on a constant basis into sensitive systems to trigger silent killing of basic functional units.
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| 40. |
- Sharma, S. R., et al.
(författare)
-
Frequency spectra of various events pertinent to lightning cloud flashes obtained from wavelet transform technique and ratified by narrow band measurement technique
- 2021
-
Ingår i: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier. - 1364-6826 .- 1879-1824. ; 220
-
Tidskriftsartikel (refereegranskat)abstract
- In the present study, frequency spectra of the electric field corresponding to the various cloud events, such as, initial breakdown process, regular pulse bursts, chaotic pulse trains and recoil streamers have been analysed. For the purpose, electric field radiated by cloud flashes were obtained simultaneously by a wide bandwidth antenna system and two narrow bandwidth antenna systems tuned at 3 MHz and 30 MHz. The frequency spectra of the broad band electric field signatures were obtained by using the wavelet transform technique and were compared with the magnitudes of the narrow band signals at the given central frequencies. To the best of our knowledge, it is the first study in which frequency spectra is obtained by transforming the time domain signal using wavelet transform technique and ratified by narrow bandwidth system for the cloud flashes. Fifteen cloud flashes pertinent to the Swedish thunderstorms were selected for the purpose. It is found that, the cloud flashes radiate at frequencies as low as 3 kHz to as high as a few tens of Mega Hertz (MHz). Electric field radiation corresponding to the initial breakdown process were found to radiate in the frequency range of 50 kHz to 5 MHz on the average, maximum energy is being radiated in the frequency range of 500 kHz to 5 MHz. Similarly, the final stage corresponding to the regular pulse bursts was found to radiate in the frequency range of 50 kHz to 5 MHz and that corresponding to the chaotic pulse trains was found to be in the range of 100 kHz to 5 MHz. Whereas, the very narrow pulses at the final stage, that can be termed as pulses corresponding recoil streamers (or Q-streamers) were found to radiate in the frequency range of 50 kHz to well above 10 MHz. Q-streamers can be considered as the strongest source of very high frequency and is justified by the simultaneous measurement of the electric fields at very high frequency (30 MHz) narrow bandwidth system. Rectification of the biasness of the conventional wavelet power spectrum has also been performed, however, no significant change in the spectrum was observed. Therefore, this study provides a strong basis for applying the wavelet transform technique without employing large number of narrowband system to acquire frequency domain information of lightning phenomena.
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| 41. |
- Srinivasan, Venkatesh, et al.
(författare)
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Modeling and Assessment of Lightning Hazards to Humans in Heritage Monuments in India and Sri Lanka
- 2020
-
Ingår i: IEEE Access. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2169-3536. ; 8, s. 228032-228048
-
Tidskriftsartikel (refereegranskat)abstract
- Lightning is one of the inevitable disastrous phenomena which in addition to damaging tall edifices, might also consequently endanger humans due to lightning-human interactions. This research focuses on analyzing lightning hazards to humans in the vicinity of heritage monuments in India and Sri Lanka. Five monuments which include three giant stupas namely Ruwanweliseya, Jethawanaramaya and Abayagiriya from Sri Lanka and two large temples namely Brihadishvara Temple and Gangaikonda Cholapuram from India have been chosen for investigation. Lightning-human interaction mechanisms namely direct strike, side flash, aborted upward leader, step and touch voltages have been investigated for the most onerous scenario on humans in the vicinity of the monuments. Firstly, the electro-geometric model as stipulated in standards has been implemented to ascertain the effectiveness of lightning protection to the structures. Subsequently, the study has been extended to the computation of step and touch voltages utilizing lightning current and electrostatic models based on Finite Element Method (FEM) using COMSOL Multi-physics(R). Detailed plots of electric field and voltage distribution of lightning on humans due to a typical lightning current of 30 kA have been obtained. The final study involves assessment of current through humans which is estimated based on lumped R-C human model representation using OrCAD Cadence(R). The analyses reveal that humans are invariably shielded against direct strikes whereas effects due to side flashes are minimal. During strikes to the monuments, high voltage may appear due to step and touch potential under dry conditions, though such effects could be mitigated by appropriate earthing system.
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| 42. |
- Sunjerga, Antonio, et al.
(författare)
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On the Initiation of Upward Negative Lightning by Nearby Lightning Activity : An Analytical Approach
- 2021
-
Ingår i: Journal of Geophysical Research - Atmospheres. - : American Geophysical Union (AGU). - 2169-897X .- 2169-8996. ; 126:5
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Tidskriftsartikel (refereegranskat)abstract
- Upward lightning occurs generally from tall structures. The mechanism of the initiation of upward lightning is not yet fully understood. Upward lightning can be classified into two categories based on either the absence or the presence of other lightning activity prior to the upward flash. This work proposes an explanation of how upward lightning flashes can be triggered by nearby lightning activity. It is generally thought that the lightning activity prior to the flash will intensify the electric field at the tip of the tall structures. However, to the best of our knowledge, no attempt has been made to evaluate theoretically this hypothesis. In this paper, we derive analytically the electric field enhancement on the ground (or at the top of tall structures) based on different triggering scenarios. These fields are later used in a simplified corona model to evaluate if they are able to trigger upward lightning. It is shown that both slow processes such as leader propagation and faster return strokes can trigger an upward negative flash from relatively short structures of a few tens of meters, even without any slowly varying background electric field. This study confirms theoretically experimental observations and it provides new insights into the mechanisms of initiation of upward flashes from tall structures.
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| 43. |
- Wooi, Chin-Leong, et al.
(författare)
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Observations of X-rays in 4-meters long laboratory sparks under positive lightning impulse
- 2021
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Ingår i: 2021 35TH INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP) AND XVI INTERNATIONAL SYMPOSIUM ON LIGHTNING PROTECTION (SIPDA). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781665423465
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Konferensbidrag (refereegranskat)abstract
- In this paper, the observation of X-rays in 4-meters long laboratory sparks is presented for the first time. In this study, a total of 20 standard positive lightning impulse voltages (1.2/50 mu s) with measured peak voltages between 3.0 to 3.2 MV were applied across 4-m long horizontal air gap of sphere-sphere configuration with 50-cm spheres. The results show that most of the X-ray emission were detected at about 12 mu s after the applications of the lightning impulse voltage during the rising part of the voltage or at around the peak of the voltage. Compared to previous shorter gaps studies, the longer air gaps seem leads to a delay in X-ray occurrence time. X-rays appeared at about 1-2 mu s after the applications of lightning impulse voltage which is slightly delayed compared to some of the previous shorter gap's studies. This study also finds an increase in the X-ray emission rate and deposited energies of Xrays in the case of higher applied peak voltages. Higher applied peak voltages seemed to change the X-rays appearance time as well. Additionally, multiple peaks X-rays pulses were observed near to the peak of the voltage in this study.
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