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  • 1. Ahmad, M R
    et al.
    Esa, M R M
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Measurement of bit error rate at 2,4 GHz due to lightning interference2012In: Proceeding of the 31st International Conference on Lightning Protection ICLP 2012, 2012Conference paper (Refereed)
    Abstract [en]

    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.

  • 2.
    Ahmad, Mohd Riduan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Universiti Teknikal Malaysia Melaka.
    Interaction of Lightning Flashes with Wireless Communication Networks: Special Attention to Narrow Bipolar Pulses2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    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.

    List of papers
    1. Signatures of Narrow Bipolar Pulses as Part of Cloud-to-Ground Flashes in Tropical Thunderstorms
    Open this publication in new window or tab >>Signatures of Narrow Bipolar Pulses as Part of Cloud-to-Ground Flashes in Tropical Thunderstorms
    2014 (English)In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824Article in journal (Refereed) Submitted
    Keywords
    Narrow bipolar pulse; Return stroke; Tropical thunderstorm.
    National Category
    Meteorology and Atmospheric Sciences Engineering and Technology
    Research subject
    Engineering Science with specialization in Atmospheric Discharges
    Identifiers
    urn:nbn:se:uu:diva-233624 (URN)
    Available from: 2014-10-07 Created: 2014-10-07 Last updated: 2017-12-05
    2. Narrow bipolar pulses and associated microwave radiation
    Open this publication in new window or tab >>Narrow bipolar pulses and associated microwave radiation
    2013 (English)Conference paper, Published paper (Refereed)
    Place, publisher, year, edition, pages
    Stockholm: , 2013
    National Category
    Engineering and Technology
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-212898 (URN)
    Conference
    Progress in Electromagnetics Research Symposium
    Available from: 2013-12-16 Created: 2013-12-16 Last updated: 2015-01-23
    3. Electric Field Signature of Narrow Bipolar Pulse Observed in Sweden
    Open this publication in new window or tab >>Electric Field Signature of Narrow Bipolar Pulse Observed in Sweden
    Show others...
    2014 (English)In: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895Article in journal (Refereed) Submitted
    Keywords
    Electric field; Narrow bipolar pulse; Sweden.
    National Category
    Meteorology and Atmospheric Sciences Engineering and Technology
    Research subject
    Engineering Science with specialization in Atmospheric Discharges
    Identifiers
    urn:nbn:se:uu:diva-233636 (URN)
    Available from: 2014-10-07 Created: 2014-10-07 Last updated: 2017-12-05
    4. Latitude Dependence of Narrow Bipolar Pulse Emissions
    Open this publication in new window or tab >>Latitude Dependence of Narrow Bipolar Pulse Emissions
    Show others...
    2015 (English)In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 128, p. 40-45Article in journal (Refereed) Published
    Keywords
    Latitude; Narrow bipolar pulse; Thunderstorm.
    National Category
    Meteorology and Atmospheric Sciences Engineering and Technology
    Research subject
    Engineering Science with specialization in Atmospheric Discharges
    Identifiers
    urn:nbn:se:uu:diva-233638 (URN)10.1016/j.jastp.2015.03.005 (DOI)000355717500005 ()
    Available from: 2014-10-07 Created: 2014-10-07 Last updated: 2017-12-05Bibliographically approved
    5. Similarity between the Initial Breakdown Pulses of Negative Ground Flash and Narrow Bipolar Pulses
    Open this publication in new window or tab >>Similarity between the Initial Breakdown Pulses of Negative Ground Flash and Narrow Bipolar Pulses
    2014 (English)In: 2014 INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP), IEEE conference proceedings, 2014, p. 810-813Conference paper, Published paper (Refereed)
    Abstract [en]

    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.

    Place, publisher, year, edition, pages
    IEEE conference proceedings, 2014
    Keywords
    Narrow bipolar pulse; Preliminary breakdown pulse; Relativistic runaway electron avalanches.
    National Category
    Meteorology and Atmospheric Sciences Engineering and Technology
    Research subject
    Engineering Science with specialization in Atmospheric Discharges
    Identifiers
    urn:nbn:se:uu:diva-233639 (URN)000358572100153 ()978-1-4799-3544-4 (ISBN)
    Conference
    International Conference on Lightning Protection (ICLP), OCT 11-18, 2014, Tsinghua Univ, Shanghai, PEOPLES R CHINA
    Available from: 2014-10-07 Created: 2014-10-07 Last updated: 2015-09-03Bibliographically approved
    6. Lightning interference in multiple antennas wireless communication systems
    Open this publication in new window or tab >>Lightning interference in multiple antennas wireless communication systems
    Show others...
    2012 (English)In: Journal of Lightning Research, ISSN 1652-8034, Vol. 4, p. 155-165Article in journal (Refereed) Published
    Abstract [en]

    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.

    Place, publisher, year, edition, pages
    Bentham open, 2012
    National Category
    Meteorology and Atmospheric Sciences Engineering and Technology
    Research subject
    Engineering Science with specialization in Atmospheric Discharges
    Identifiers
    urn:nbn:se:uu:diva-190902 (URN)
    Available from: 2013-01-09 Created: 2013-01-09 Last updated: 2016-02-03
    7. Interference from cloud-to-ground and cloud flashes in wireless communication system
    Open this publication in new window or tab >>Interference from cloud-to-ground and cloud flashes in wireless communication system
    2014 (English)In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 113, p. 237-246Article in journal (Refereed) Published
    Abstract [en]

    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.

    Keywords
    Bit error rate, Cloud flash, Cloud-to-ground flash, Interference, Microwave radiation, Wireless system
    National Category
    Electrical Engineering, Electronic Engineering, Information Engineering
    Identifiers
    urn:nbn:se:uu:diva-228679 (URN)10.1016/j.epsr.2014.03.022 (DOI)000337554200032 ()
    Available from: 2014-07-22 Created: 2014-07-21 Last updated: 2017-12-05Bibliographically approved
  • 3.
    Ahmad, Mohd Riduan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Esa, Mona Riza Binti Mohd
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Narrow bipolar pulses and associated microwave radiation2013Conference paper (Refereed)
  • 4.
    Ahmad, Mohd Riduan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Esa, Mona Riza Binti Mohd
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Dutkiewicz, Eryk
    Interference from cloud-to-ground and cloud flashes in wireless communication system2014In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 113, p. 237-246Article in journal (Refereed)
    Abstract [en]

    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.

  • 5.
    Ahmad, Mohd Riduan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Esa, Mona Riza Binti Mohd
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Dutkiewicz, Eryk
    Performance analysis of audio streaming over lightning-interfered MIMO channels2012Conference paper (Refereed)
  • 6.
    Ahmad, Mohd Riduan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Esa, Mona Riza Binti Mohd
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Dutkiewicz, E.
    Wireless Communications and Networking Lab, Macquarie University, Sydney, Australien.
    Lightning interference in multiple antennas wireless communication systems2012In: Journal of Lightning Research, ISSN 1652-8034, Vol. 4, p. 155-165Article in journal (Refereed)
    Abstract [en]

    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.

  • 7.
    Ahmad, Mohd Riduan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Mohd Esa, Mona Riza Binti
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hettiarachchi, Pasan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Preliminary Observations of Lightning Signature At 2400 MHz in Sweden Thunderstorm2012In: / [ed] BinSulaiman, HA; Jaafar, A, NEW YORK: IEEE , 2012, p. 88-91Conference paper (Refereed)
    Abstract [en]

    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.

  • 8.
    Ahmad, Mohd Riduan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Mohd Esa, Mona Riza
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Occurrence of Narrow Bipolar Event as Part of Cloud-to-Ground Flash in Tropical Thunderstorms2014Conference paper (Refereed)
  • 9.
    Ahmad, Mohd Riduan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Mohd Esa, Mona Riza
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Similarity between the Initial Breakdown Pulses of Negative Ground Flash and Narrow Bipolar Pulses2014In: 2014 INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP), IEEE conference proceedings, 2014, p. 810-813Conference paper (Refereed)
    Abstract [en]

    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.

  • 10.
    Ahmad, Mohd Riduan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Mohd Esa, Mona Riza
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Baharudin, Zikri Abadi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Universiti Teknikal Malaysia Melaka.
    Hettiarachchi, Pasan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Latitude Dependence of Narrow Bipolar Pulse Emissions2015In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 128, p. 40-45Article in journal (Refereed)
  • 11.
    Ahmad, Mohd Riduan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Mohd Esa, Mona Riza
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hettiarachchi, Pasan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Baharudin, Zikri Abadi
    Universiti Teknikal Malaysia Melaka.
    Electric Field Signature of Narrow Bipolar Pulse Observed in Sweden2014In: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895Article in journal (Refereed)
  • 12.
    Ahmad, Mohd Riduan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Mohd Esa, Mona Riza
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Johari, Dalina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ismail, Mohd Muzafar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Chaotic Pulse Train in Cloud-to-Ground and Cloud Flashes of Tropical Thunderstorms2014Conference paper (Refereed)
    Abstract [en]

    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.

  • 13.
    Ahmad, Mohd Riduan
    et al.
    UTEM, Durian Tunggal, Melaka, Malaysia.
    Periannan, Dinesh
    UTEM, Durian Tunggal, Melaka, Malaysia.
    Sabri, Muhammad Haziq Mohammad
    UTEM, Durian Tunggal, Melaka, Malaysia.
    Abd Aziz, Mohamad Zoinol Abidin
    UTEM, Durian Tunggal, Melaka, Malaysia.
    Esa, Mona Riza Mohd
    UTM, Inst Voltan Tinggi & Arus Tinggi IVAT, Johor Bharu, Malaysia.
    Lu, Gaopeng
    Chinese Acad Sci, Beijing, Peoples R China.
    Zhang, Hongbo
    Chinese Acad Sci, Beijing, Peoples R China.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Emission Heights of Narrow Bipolar Events in a Tropical Storm over the Malacca Strait2017In: 2017 International Conference On Electrical Engineering And Computer Science (Icecos), IEEE , 2017, p. 305-309Conference paper (Refereed)
    Abstract [en]

    Emission heights for narrow bipolar events (NBEs) have been reported mostly from observations at mid latitudes but none have been reported from tropical regions. In this paper, we are reporting for the first time the heights of NBE emissions from a tropical storm over the Malacca Strait, a narrow water passage between the Malay Peninsula and Sumatra Island. A total of 49 positive NBEs (+NBEs) were detected from the storm. The NBE activity can be divided into two stages according to the emission heights and radar reflectivity data. The first stage (or S1) lasted for only 6 minutes, started with the first detected NBE, and produced 20 NBEs (41%). The emission heights ranged between 12.0 and 16.7 km. Radar reflectivity data showed that the storm reached maximum values at 55 dBZ within the period S1. In contrast, the second stage (S2) lasted longer (32 minutes) and produced 29 NBEs (59%). The emission heights were lower and ranged from 8.5 to 13.7 km. Radar reflectivity data showed that the storm reached maximum values at 50 dBZ within the period S2.

  • 14.
    Ahmad, M.R.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rashid, M.
    Aziz, M.H.A.
    Esa, M.R.M.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Dutkiewicz, E.
    Analysis of Lightning-induced Transient in 2.4 GHz Wireless Communication System2011In: Proceeding of IEEE International Conference on Space Science and Communication (IconSpace), Penang, Malaysia, pp225-230, 2011Conference paper (Refereed)
  • 15.
    Ahmad, Noor Azlinda
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Broadband and HF Radiation from Cloud Flashes and Narrow Bipolar Pulses2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    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 -1 frequency dependence within the interval of 10 kHz to approximately 10 MHz. This is in contrast to the standard -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.

    List of papers
    1. The first electric field pulse of cloud and cloud-to-ground lightning discharges
    Open this publication in new window or tab >>The first electric field pulse of cloud and cloud-to-ground lightning discharges
    Show others...
    2010 (English)In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 72, no 2-3, p. 143-150Article in journal (Refereed) Published
    Abstract [en]

    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.

    Keywords
    Cloud discharges, Electromagnetic field, Lightning, Electric field pulses
    National Category
    Meteorology and Atmospheric Sciences Engineering and Technology
    Research subject
    Engineering Science with specialization in Atmospheric Discharges
    Identifiers
    urn:nbn:se:uu:diva-140337 (URN)10.1016/j.jastp.2009.11.001 (DOI)
    Available from: 2011-01-05 Created: 2011-01-05 Last updated: 2017-12-11
    2. Radiation Field Spectra of Long-duration Cloud Flashes
    Open this publication in new window or tab >>Radiation Field Spectra of Long-duration Cloud Flashes
    (English)In: IEEE transactions on electromagnetic compatibility (Print), ISSN 0018-9375, E-ISSN 1558-187XArticle in journal (Refereed) Submitted
    Abstract [en]

    The radiation electric fields produced by long-duration cloud flashes have been Fourier analyzed to determined the frequency spectrum in the range of 10 kHz to 10 MHz. The flashes were recorded within a distance of less than 20 km. The spectrum was normalized to 50 km distance and it shows a f-1 dependence within the entire frequency range.

    Identifiers
    urn:nbn:se:uu:diva-150952 (URN)
    Available from: 2011-04-08 Created: 2011-04-08 Last updated: 2017-12-11
    3. Characteristics of narrow bipolar pulses observed in Malaysia
    Open this publication in new window or tab >>Characteristics of narrow bipolar pulses observed in Malaysia
    Show others...
    2010 (English)In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 72, no 5-6, p. 534-540Article in journal (Refereed) Published
    Abstract [en]

    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.

    Keywords
    Narrow bipolar pulses, Lightning, Cloud discharges, Electric field
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-137067 (URN)10.1016/j.jastp.2010.02.006 (DOI)000276428600020 ()
    Available from: 2010-12-15 Created: 2010-12-15 Last updated: 2017-12-11Bibliographically approved
    4. Some features of electric field waveform of Narrow Bipolar Pulses
    Open this publication in new window or tab >>Some features of electric field waveform of Narrow Bipolar Pulses
    (English)In: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895Article in journal (Refereed) Submitted
    Abstract [en]

    Narrow Bipolar Pulses (NBPs) are generated by intra-cloud discharge processes and they are of interest due to their strong broadband and high frequency (HF) emissions. In this study, we present some features of electric field waveform of NBPs which have not been reported in the literature.  The HF emission was observed to begin simultaneously with the onset of NBPs indicating no streamers or stepped-leader process was taking place before the initiation of NBPs. The electric field waveforms of NBPs were characterized by many fine peaks embedded intermittently on the rising and decaying edge of NBPs suggesting that some small scale electrical discharges were involved during the formation of NBPs.

     

    Identifiers
    urn:nbn:se:uu:diva-150953 (URN)
    Available from: 2011-04-08 Created: 2011-04-08 Last updated: 2017-12-11
  • 16. Ahmad, Noor Azlinda
    et al.
    Baharudin, Zikri A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fernando, M.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Radiation field spectra of long-duration cloud flashes2015In: Atmospheric Science Letters, ISSN 1530-261X, E-ISSN 1530-261X, Vol. 16, no 2, p. 91-95Article in journal (Refereed)
    Abstract [en]

    The preliminary results of radiation electric fields produced by long-duration cloud flashes have been Fourier analyzed to determine the frequency spectrum in the range of 10kHz-10MHz. The flashes were recorded within a distance of less than 20km. The spectrum was normalized to 50km distance and it shows a f(-1) dependence within the entire frequency range.

  • 17.
    Ahmad, Noor Azlinda
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology.
    Baharudin, Zikri Abadi
    Uppsala University, Disciplinary Domain of Science and Technology, För teknisk-naturvetenskapliga fakulteten gemensamma enheter.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, För teknisk-naturvetenskapliga fakulteten gemensamma enheter.
    Fernando, Mahendra
    Department of Physics.
    Radiation Field Spectra of Long-duration Cloud FlashesIn: IEEE transactions on electromagnetic compatibility (Print), ISSN 0018-9375, E-ISSN 1558-187XArticle in journal (Refereed)
    Abstract [en]

    The radiation electric fields produced by long-duration cloud flashes have been Fourier analyzed to determined the frequency spectrum in the range of 10 kHz to 10 MHz. The flashes were recorded within a distance of less than 20 km. The spectrum was normalized to 50 km distance and it shows a f-1 dependence within the entire frequency range.

  • 18.
    Ahmad, Noor Azlinda
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology.
    Baharudin, Zikri Abadi
    Uppsala University, Disciplinary Domain of Science and Technology, För teknisk-naturvetenskapliga fakulteten gemensamma enheter.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, För teknisk-naturvetenskapliga fakulteten gemensamma enheter.
    Fernando, Mahendra
    Some features of electric field waveform of Narrow Bipolar PulsesIn: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895Article in journal (Refereed)
    Abstract [en]

    Narrow Bipolar Pulses (NBPs) are generated by intra-cloud discharge processes and they are of interest due to their strong broadband and high frequency (HF) emissions. In this study, we present some features of electric field waveform of NBPs which have not been reported in the literature.  The HF emission was observed to begin simultaneously with the onset of NBPs indicating no streamers or stepped-leader process was taking place before the initiation of NBPs. The electric field waveforms of NBPs were characterized by many fine peaks embedded intermittently on the rising and decaying edge of NBPs suggesting that some small scale electrical discharges were involved during the formation of NBPs.

     

  • 19.
    Ahmad, Noor Azlinda
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fernando, Mahendra
    Baharudin, Z. A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Saleh, Ziad
    Dwyer, Joseph R.
    Rassoul, Hamid K.
    The first electric field pulse of cloud and cloud-to-ground lightning discharges2010In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 72, no 2-3, p. 143-150Article in journal (Refereed)
    Abstract [en]

    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.

  • 20.
    Ahmad, Noor Azlinda
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fernando, Mahendra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Baharudin, Zikri A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ahmad, H.
    Malek, Z. Abdul
    Characteristics of narrow bipolar pulses observed in Malaysia2010In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 72, no 5-6, p. 534-540Article in journal (Refereed)
    Abstract [en]

    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.

  • 21.
    Ahmad, Noor Azlinda
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fernando, Mahendra
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    ON THE DERIVATIVES OF NARROW BIPOLAR PULSES2010Conference paper (Refereed)
  • 22. Akyuz, Mose
    et al.
    Cortet, P.P.
    Cooray, Vernon
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Electricity. Avdelningen för elektricitetslära och åskforskning.
    Positive Streamer Discharges along Liquid Dielectric Surfaces: Effect of Dielectric Constant and Surface Properties2005In: IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 12, no 3, p. 579-585Article in journal (Refereed)
  • 23.
    Akyuz, Mose
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Larsson, Anders
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Franke, Axel
    Characteristics of Laser-triggered Electric Discharges in Air2005In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 12, no 5, p. 1060-1070Article in journal (Refereed)
  • 24. Amarasinghe, Dulan
    et al.
    Sonnadara, Upul
    Berg, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Channel tortuosity of long laboratory sparks2007In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 65, no 8, p. 521-526Article in journal (Refereed)
    Abstract [en]

    Channel tortuosity of 50 cm long laboratory sparks were measured by analyzing a set of images taken by three cameras. The cameras were placed at a radial distance of 200 cm from the spark gap. The angle between any two cameras was 120 degrees. The sparks were generated between a steel rod and. a plane electrode. The distribution of the direction change of the channel was found to be Gaussian with a standard deviation of 15.3 degrees. The average tortuosity of the channel defined as the mean absolute value of the direction change was 11.8 +/- 1.4 degrees, which is smaller than the average tortuosity of natural lightning and close to the tortuosity of triggered lightning. The average tortuosity is dependent on the segment length used in calculating the direction change. A gradual increase in the average tortuosity (0.08 degrees/cm) was seen when the sparks propagated towards the plane electrode.

  • 25. Amarasinghe, Dulan
    et al.
    Sonnadara, Upul
    Berg, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Correlation between brightness and channel currents of electrical discharges2007In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 14, no 5, p. 1154-1160Article in journal (Refereed)
    Abstract [en]

    Channel brightness of 500 mm long electrical discharges were measured by analyzing a set of digitized images taken by 3 cameras placed symmetrically around a discharge gap at a radial distance of 200 cm from the axis of the spark. The sparks were generated between a steel rod and a plane electrode. The distribution of the brightness across the channel represented a Gaussian distribution. A linear correlation was seen between the channel brightness measured by different cameras looking at the same spark channel. No correlation was seen between the channel brightness and the channel depth (direction perpendicular to the camera plane). The measured peak current and the brightness of the main spark channel show a high degree of correlation (R-2=0.97). The sum of brightness of branches was equal to the brightness of the parent channel. One can use this result to calculate the relative distribution of branch currents in complex electrical discharges including natural lightning flashes. If the current in the parent channel is known, branch currents can be calculated by measuring the optical intensities using photographic techniques.

  • 26. Amarasinghe, Dulan
    et al.
    Sonnadara, Upul
    Berg, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fractal dimension of long electrical discharges2015In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 73, p. 33-37Article in journal (Refereed)
    Abstract [en]

    The fractal dimension of 500 mm long electrical discharges is presented by analyzing a set of photographic images. Three popular fractal dimension estimation techniques, box counting, sandbox and correlation function methods were used to estimate the fractal dimension of the discharge channels. To remove the apparent thickness due to varying magnitudes of current in the discharge channels, edge detection algorithms were utilized. The estimated fractal dimensions for box counting, sandbox and correlation function for long laboratory sparks were 1.20 +/- 0.06,1.66 +/- 0.05 and 1.52 +/- 0.12 respectively. Within statistical uncertainties, the estimated fractal dimensions of positive and negative polarities agreed very well. (C) 2014 Elsevier B.V. All rights reserved.

  • 27. Arevalo, L.
    et al.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Corona charge produced by thundercloud fields in grounded rods2012In: 31st International Conference on Lightning Protection ICLP 2012, 2012, p. 6344365-Conference paper (Refereed)
    Abstract [en]

    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.

  • 28.
    Arevalo, L.
    et al.
    ABB Power Syst HVDC, R&D Dept, Ludvika, Sweden..
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    The mesh method in lightning protection analyzed from a lightning attachment model2016In: 2016 33RD INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP), 2016Conference paper (Refereed)
    Abstract [en]

    Based on the well-known rolling sphere method, international standards recommend the location of the external lightning protection system of structures. The design of the external lightning protection system of structures of height of less than 60 m can be done by installing a mesh on top of a roof of the structure or by creating a mesh with wires at certain distance from the roof of the structure. The prospective downward leader current that the mesh can incept depends on the size of the mesh and the current magnitude is given as recommendation in the international standards. This paper analyses the relation prospective negative downward leader current vs. mesh size from a lightning attachment model. The model is applied to a perfectly grounded structure with maximum height of 50 m protected by two different external lightning protection systems recommended by the international standards. The results showed difference on magnitude of the prospective downward leader current the standards recommend and the ones obtained using the lightning attachment model for meshes of shorter size. Discrepancies concerning the minimum downward leader current that can be incepted by a mesh made by wires located at certain distance from the ground structure and a mesh located on top of the building are obtained.

  • 29.
    Arevalo, Liliana
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Numerical Simulations of Long Spark and Lightning Attachment2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    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.

    List of papers
    1. Modelling of Positive Discharges in Laboratory Gaps under Switching impulses
    Open this publication in new window or tab >>Modelling of Positive Discharges in Laboratory Gaps under Switching impulses
    2008 (English)Conference paper, Published paper (Refereed)
    Place, publisher, year, edition, pages
    Cardiff, UK: , 2008
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-113403 (URN)
    Conference
    XVII International Conference on Gas Discharges and Their applications
    Available from: 2010-01-28 Created: 2010-01-28 Last updated: 2016-04-12Bibliographically approved
    2. Breakdown effect on long gaps under switching impulses statistical variation
    Open this publication in new window or tab >>Breakdown effect on long gaps under switching impulses statistical variation
    2008 (English)Conference paper, Published paper (Refereed)
    Place, publisher, year, edition, pages
    Uppsala, Sweden: , 2008
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-113402 (URN)
    Conference
    29th International Conference on Lightning Protection
    Available from: 2010-01-28 Created: 2010-01-28 Last updated: 2016-04-12Bibliographically approved
    3. Breakdown times and voltages probability calculation using a simplified numerical methodology
    Open this publication in new window or tab >>Breakdown times and voltages probability calculation using a simplified numerical methodology
    2008 (English)Conference paper, Published paper (Refereed)
    Place, publisher, year, edition, pages
    Florianopolis Brazil: , 2008
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-113401 (URN)
    Conference
    International Conference on Grounding and Earthing and 3rd International Conference on Lightning Physics and Effects
    Available from: 2010-01-28 Created: 2010-01-28 Last updated: 2016-04-12Bibliographically approved
    4. Numerical simulation of long laboratory sparks generated by positive switching impulses
    Open this publication in new window or tab >>Numerical simulation of long laboratory sparks generated by positive switching impulses
    2009 (English)In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 67, no 2-3, p. 228-234Article in journal (Refereed) Published
    Abstract [en]

    A numerical methodology using two different leader channel criteria has been implemented. The methodology is based on Bondiou and Gallimberti's proposition [A. Bondiou, I. Gallimberti, Theoretical modelling of the development of the positive spark in long spark, J. Phys. D: Appl. Phys. 27 (1994) 1252-1266]. The leader channel criteria used are Rizk engineering criterion [Rizk, A model for switching impulse leader inception and breakdown of long air gaps, IEEE Trans. Power Deliv., 4(1) (1989)] and Local thermodynamic - L.T.E. - physical concept [I. Gallimberti, The mechanism of the long spark formation, Colloque C7, J. Phys. (supplement au nro 7, Tome 40) (July 1979) C7-193]. The methodology was tested in three different cases; a deterministic case, a statistical variation and a typical constant level test. Deterministic calculation considered corona inception using stabilization corona electric field criterion of Gallimberti [I. Gallimberti, The mechanism of the long spark formation, Colloque C7, J. Phys. (supplement au nro 7, Tome 40) (July 1979) C7-193] and the leader moving as segments. The statistical simulation has two different statistical delays, one at inception and the other due to the tortuous characteristics of the leader channel. The constant level test consists of 200 positive switching impulses with the same characteristics such as maximum applied voltage, time to crest and time to fall. Time to breakdown and breakdown voltage were found based on the results obtained from the constant level test characteristics. All the numerical results presented are based on experimental conditions reported in [Les Renardières Group, Research on long gap discharges at Les Renardières, Electra N 35 (1973)] from the world class research group namely Les Renardieres Group.

    Keywords
    Discharge, Leader, Modeling, Switching
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-113133 (URN)10.1016/j.elstat.2008.12.022 (DOI)000266019500029 ()0304-3886 (ISBN)
    Available from: 2010-01-25 Created: 2010-01-25 Last updated: 2017-12-12Bibliographically approved
    5. LABORATORY LONG GAPS SIMULATION CONSIDERING A VARIABLE CORONA REGION
    Open this publication in new window or tab >>LABORATORY LONG GAPS SIMULATION CONSIDERING A VARIABLE CORONA REGION
    2010 (English)Conference paper, Published paper (Refereed)
    Place, publisher, year, edition, pages
    Cagliary, Italy: , 2010
    National Category
    Engineering and Technology
    Research subject
    Engineering Science with specialization in Atmospheric Discharges
    Identifiers
    urn:nbn:se:uu:diva-140390 (URN)
    Conference
    30TH International Conference on Lightning Protection, ICLP
    Available from: 2011-01-05 Created: 2011-01-05 Last updated: 2016-03-03
    6. A RELIABLE NUMERICAL METHOD FOR THE CALCULATION OF BREAKDOWN VOLTAGES
    Open this publication in new window or tab >>A RELIABLE NUMERICAL METHOD FOR THE CALCULATION OF BREAKDOWN VOLTAGES
    2010 (English)Conference paper, Published paper (Refereed)
    Place, publisher, year, edition, pages
    Cagliary, Italy: , 2010
    National Category
    Engineering and Technology
    Research subject
    Engineering Science with specialization in Atmospheric Discharges
    Identifiers
    urn:nbn:se:uu:diva-140391 (URN)
    Conference
    30TH International Conference on Lightning Protection, ICLP
    Available from: 2011-01-05 Created: 2011-01-05 Last updated: 2014-12-10
    7. A new static calculation of the streamer region for long spark gaps
    Open this publication in new window or tab >>A new static calculation of the streamer region for long spark gaps
    2012 (English)In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 70, no 1, p. 15-19Article in journal (Refereed) Published
    Abstract [en]

    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.

    Keywords
    charge, leader, Streamer, Electrical charge, Electric field, Corona inception, Discharge
    National Category
    Electrical Engineering, Electronic Engineering, Information Engineering
    Research subject
    Electricity, Esp The Study Of Transients and Discharges; Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-150528 (URN)10.1016/j.elstat.2011.07.013 (DOI)000300804300003 ()
    Available from: 2011-03-31 Created: 2011-03-31 Last updated: 2017-12-11Bibliographically approved
    8. The development of long spark gaps: Simulation including a variable streamer region
    Open this publication in new window or tab >>The development of long spark gaps: Simulation including a variable streamer region
    (English)Article in journal (Refereed) Submitted
    Keywords
    Breakdown, streamer, discharge
    National Category
    Other Electrical Engineering, Electronic Engineering, Information Engineering
    Research subject
    Engineering Science with specialization in Atmospheric Discharges
    Identifiers
    urn:nbn:se:uu:diva-150531 (URN)
    Available from: 2011-03-31 Created: 2011-03-31 Last updated: 2016-03-03
    9. Reliable model for the calculation of negative leader discharges under switching impulses
    Open this publication in new window or tab >>Reliable model for the calculation of negative leader discharges under switching impulses
    2010 (English)Conference paper, Published paper (Refereed)
    Keywords
    negative streamer, space leader, breakdown
    National Category
    Other Electrical Engineering, Electronic Engineering, Information Engineering
    Research subject
    Engineering Science with specialization in Atmospheric Discharges
    Identifiers
    urn:nbn:se:uu:diva-150533 (URN)
    Conference
    36th grounding and 4th Lightning Physics conference GND&LPE
    Available from: 2011-03-31 Created: 2011-03-31 Last updated: 2016-04-18
    10. A preliminary model to simulate negative leader discharges
    Open this publication in new window or tab >>A preliminary model to simulate negative leader discharges
    (English)In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463Article in journal (Refereed) Submitted
    Keywords
    Negative streamer, pilot system, breakdown
    National Category
    Other Electrical Engineering, Electronic Engineering, Information Engineering
    Research subject
    Engineering Science with specialization in Atmospheric Discharges
    Identifiers
    urn:nbn:se:uu:diva-150532 (URN)
    Available from: 2011-03-31 Created: 2011-03-31 Last updated: 2017-12-11
    11. On the interception of lightning flashes by power transmission lines
    Open this publication in new window or tab >>On the interception of lightning flashes by power transmission lines
    2011 (English)In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 69, no 3, p. 220-227Article in journal (Refereed) Published
    Abstract [en]

    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.

    Keywords
    power system, lightning attachment, breakdown, downward leader
    National Category
    Other Electrical Engineering, Electronic Engineering, Information Engineering
    Research subject
    Engineering Science with specialization in Atmospheric Discharges
    Identifiers
    urn:nbn:se:uu:diva-150534 (URN)10.1016/j.elstat.2011.03.013 (DOI)000292230300012 ()
    Available from: 2011-03-31 Created: 2011-03-31 Last updated: 2017-12-11
    12. 'The mesh method' in lightning protection standards - Revisited
    Open this publication in new window or tab >>'The mesh method' in lightning protection standards - Revisited
    2010 (English)In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 68, no 4, p. 311-314Article in journal (Refereed) Published
    Abstract [en]

    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.

    Keywords
    Dynamic leader, Electro-geometrical method, Lightning inception, Mesh method, Upward leader, Standards
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-135183 (URN)10.1016/j.elstat.2010.03.003 (DOI)000281211700004 ()
    Available from: 2010-12-06 Created: 2010-12-06 Last updated: 2017-12-12Bibliographically approved
    13. Influence of multiple upward connecting leaders initiated from the same structure on the lightning attachment process
    Open this publication in new window or tab >>Influence of multiple upward connecting leaders initiated from the same structure on the lightning attachment process
    2009 (English)Conference paper, Published paper (Refereed)
    Keywords
    electric field, inhibit discharge, breakdown, streamer, lightning, attachment
    National Category
    Other Electrical Engineering, Electronic Engineering, Information Engineering
    Research subject
    Engineering Science with specialization in Atmospheric Discharges
    Identifiers
    urn:nbn:se:uu:diva-150535 (URN)
    Conference
    X International symposium on lightning protection - SIPDA
    Available from: 2011-03-31 Created: 2011-03-31 Last updated: 2016-04-14
    14. Interaction of multiple connecting leaders issued from a grounded structure simulated using a self consistent leader inception and propagation model SLIM
    Open this publication in new window or tab >>Interaction of multiple connecting leaders issued from a grounded structure simulated using a self consistent leader inception and propagation model SLIM
    2010 (English)In: 30TH International Conference on Lightning Protection, ICLP, Cagliary, Italy, 2010Conference paper, Published paper (Refereed)
    Place, publisher, year, edition, pages
    Cagliary, Italy: , 2010
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-142452 (URN)
    Conference
    30TH International Conference on Lightning Protection, ICLP
    Available from: 2011-01-14 Created: 2011-01-14 Last updated: 2016-04-19Bibliographically approved
  • 30.
    Arevalo, Liliana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    A preliminary model to simulate negative leader dischargesIn: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463Article in journal (Refereed)
  • 31.
    Arevalo, Liliana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    A RELIABLE NUMERICAL METHOD FOR THE CALCULATION OF BREAKDOWN VOLTAGES2010Conference paper (Refereed)
  • 32.
    Arevalo, Liliana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Influence of multiple upward connecting leaders initiated from the same structure on the lightning attachment process2009Conference paper (Refereed)
  • 33.
    Arevalo, Liliana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    LABORATORY LONG GAPS SIMULATION CONSIDERING A VARIABLE CORONA REGION2010Conference paper (Refereed)
  • 34.
    Arevalo, Liliana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    On the interception of lightning flashes by power transmission lines2011In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 69, no 3, p. 220-227Article in journal (Refereed)
    Abstract [en]

    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.

  • 35.
    Arevalo, Liliana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Preliminary study on the modelling of negative leader discharges2011In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 44, no 31, p. 315204-Article in journal (Refereed)
    Abstract [en]

    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.

  • 36.
    Arevalo, Liliana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Reliable model for the calculation of negative leader discharges under switching impulses2010Conference paper (Refereed)
  • 37. Arevalo, Liliana
    et al.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Streamer to leader transition criteria for propagation of long sparks and lightning leaders2014In: 2014 INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP), IEEE conference proceedings, 2014, p. 480-483Conference paper (Refereed)
    Abstract [en]

    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.

  • 38.
    Arevalo, Liliana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    'The mesh method' in lightning protection standards - Revisited2010In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 68, no 4, p. 311-314Article in journal (Refereed)
    Abstract [en]

    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.

  • 39.
    Arevalo, Liliana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Ludvika ULHC, ABB Power Grids Grid Integrat HVDC, Dept Res & Dev, Lyviksvagen 3, S-77180 Lyviksvagen, Sweden..
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Unstable Leader Inception Criteria of Atmospheric Discharges2017In: Atmosphere, ISSN 2073-4433, E-ISSN 2073-4433, Vol. 8, no 9, article id 156Article in journal (Refereed)
    Abstract [en]

    In the literature, there are different criteria to represent the formation of a leader channel in short and long gap discharges. Due to the complexity of the physics of the heating phenomena, and the limitations of the computational resources, a simplified criterion for the minimum amount of electrical charge required to incept an unstable leader has recently been used for modeling long gap discharges and lightning attachments. The criterion is based on the assumption that the total energy of the streamer is used to heat up the gas, among other principles. However, from a physics point of view, energy can also be transferred to other molecular processes, such as rotation, translation, and vibrational excitation. In this paper, the leader inception mechanism was studied based on fundamental particle physics and the energy balance of the gas media. The heating process of the plasma is evaluated with a detailed two-dimensional self-consistent model. The model is able to represent the streamer propagation, dark period, and unsuccessful leaders that may occur prior to the heating of the channel. The main processes that participate in heating the gas are identified within the model, indicating that impact ionization and detachment are the leading sources of energy injection, and that recombination is responsible for loss of electrons and limiting the energy. The model was applied to a well-known experiment for long air gaps under positive switching impulses reported in the literature, and used to validate models for lightning attachments and long gap discharges. Results indicate that the streamer-leader transition depends on the amount of energy transferred to the heating process. The minimum electric charge required for leader inception varies with the gap geometry, the background electric field, the reduction of electric field due to the space charge, the energy expended on the vibrational relation, and the environmental conditions, among others.

  • 40. Arevalo, Liliana
    et al.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Upward leader inception caused by a sudden change of cloud electric field2014In: 2014 INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP), IEEE conference proceedings, 2014, p. 484-487Conference paper (Refereed)
    Abstract [en]

    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.
    Arevalo, Liliana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Montano, Raul
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Breakdown times and voltages probability calculation using a simplified numerical methodology2008Conference paper (Refereed)
  • 42.
    Arevalo, Liliana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Montano, Raul
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Numerical simulation of long laboratory sparks generated by positive switching impulses2009In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 67, no 2-3, p. 228-234Article in journal (Refereed)
    Abstract [en]

    A numerical methodology using two different leader channel criteria has been implemented. The methodology is based on Bondiou and Gallimberti's proposition [A. Bondiou, I. Gallimberti, Theoretical modelling of the development of the positive spark in long spark, J. Phys. D: Appl. Phys. 27 (1994) 1252-1266]. The leader channel criteria used are Rizk engineering criterion [Rizk, A model for switching impulse leader inception and breakdown of long air gaps, IEEE Trans. Power Deliv., 4(1) (1989)] and Local thermodynamic - L.T.E. - physical concept [I. Gallimberti, The mechanism of the long spark formation, Colloque C7, J. Phys. (supplement au nro 7, Tome 40) (July 1979) C7-193]. The methodology was tested in three different cases; a deterministic case, a statistical variation and a typical constant level test. Deterministic calculation considered corona inception using stabilization corona electric field criterion of Gallimberti [I. Gallimberti, The mechanism of the long spark formation, Colloque C7, J. Phys. (supplement au nro 7, Tome 40) (July 1979) C7-193] and the leader moving as segments. The statistical simulation has two different statistical delays, one at inception and the other due to the tortuous characteristics of the leader channel. The constant level test consists of 200 positive switching impulses with the same characteristics such as maximum applied voltage, time to crest and time to fall. Time to breakdown and breakdown voltage were found based on the results obtained from the constant level test characteristics. All the numerical results presented are based on experimental conditions reported in [Les Renardières Group, Research on long gap discharges at Les Renardières, Electra N 35 (1973)] from the world class research group namely Les Renardieres Group.

  • 43.
    Arevalo, Liliana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Montano, Raul
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Roman, Franscisco
    Breakdown effect on long gaps under switching impulses statistical variation2008Conference paper (Refereed)
  • 44.
    Arevalo, Liliana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Wu, Dong
    ABB AB, Power systems HVDC, Ludvika.
    Jacobson, Björn
    ABB AB, Power Systems HVDC, Ludvika.
    A new static calculation of the streamer region for long spark gaps2012In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 70, no 1, p. 15-19Article in journal (Refereed)
    Abstract [en]

    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.

  • 45.
    Arevalo, Liliana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Wu, Dong
    Jacobson, Björn
    The development of long spark gaps: Simulation including a variable streamer regionArticle in journal (Refereed)
  • 46.
    Arevalo, Liliana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Montano, Raul
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Modelling of Positive Discharges in Laboratory Gaps under Switching impulses2008Conference paper (Refereed)
  • 47.
    Baharudin, Zikri A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ahmad, Noor Azlinda
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fernando, M.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Makela, J. S.
    Comparative study on preliminary breakdown pulse trains observed in Johor, Malaysia and Florida, USA2012In: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895, Vol. 117, p. 111-121Article in journal (Refereed)
    Abstract [en]

    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.

  • 48.
    Baharudin, Zikri A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ahmad, Noor Azlinda
    Makela, J. S.
    Fernando, Mahendra
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Negative cloud-to-ground lightning flashes in Malaysia2014In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 108, p. 61-67Article in journal (Refereed)
    Abstract [en]

    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.

  • 49.
    Baharudin, Zikri A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fernando, M.
    Dept of Physics, University of Colombo, Sri Lanka.
    Ahmad, Noor Azlinda
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Mäkelä, J. S.
    Nokia OY, Salo, Finland.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Electric field changes generated by the preliminary breakdown for the negative cloud-to-ground lightning flashes in Malaysia and Sweden2012In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 84-85, p. 15-24Article in journal (Refereed)
    Abstract [en]

    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.

  • 50.
    Baharudin, Zikri Abadi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Characterizations of ground flashes from tropic to northern region2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    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.

    List of papers
    1. Comparative study on preliminary breakdown pulse trains observed in Johor, Malaysia and Florida, USA
    Open this publication in new window or tab >>Comparative study on preliminary breakdown pulse trains observed in Johor, Malaysia and Florida, USA
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    2012 (English)In: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895, Vol. 117, p. 111-121Article in journal (Refereed) Published
    Abstract [en]

    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.

    Keywords
    Preliminary breakdown pulses, PB/RS ratio, PB-RS separation
    National Category
    Engineering and Technology
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-184450 (URN)10.1016/j.atmosres.2012.01.012 (DOI)000309300100015 ()
    Available from: 2012-11-09 Created: 2012-11-07 Last updated: 2017-12-07Bibliographically approved
    2. Electric field changes generated by the preliminary breakdown for the negative cloud-to-ground lightning flashes in Malaysia and Sweden
    Open this publication in new window or tab >>Electric field changes generated by the preliminary breakdown for the negative cloud-to-ground lightning flashes in Malaysia and Sweden
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    2012 (English)In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 84-85, p. 15-24Article in journal (Refereed) Published
    Abstract [en]

    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.

    Keywords
    Initiation position, Slow field changes, Close ground flashes, Preliminary breakdown process
    National Category
    Meteorology and Atmospheric Sciences Engineering and Technology
    Research subject
    Engineering Science with specialization in Atmospheric Discharges
    Identifiers
    urn:nbn:se:uu:diva-182547 (URN)10.1016/j.jastp.2012.04.009 (DOI)000308512100003 ()
    Available from: 2012-10-11 Created: 2012-10-11 Last updated: 2017-12-07
    3. Electric field changes generated by preliminary breakdown pulse for positive lightning ground flashes in Sweden
    Open this publication in new window or tab >>Electric field changes generated by preliminary breakdown pulse for positive lightning ground flashes in Sweden
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    (English)Manuscript (preprint) (Other academic) [Artistic work]
    Abstract [en]

    This is the new study of the electric field changes generated by the preliminary breakdown for positive cloud-to-ground flashes which concerning on the association of slow field changes in preliminary breakdown process. In this study, a 107 positive cloud-to-ground lightning flashes recorded from the total of 14 thunderstorms generated by the whole flash were examined. The electric fields were measured with nanosecond resolution by using the slow electric field, fast electric field and narrowband radiation field at 3 and 30 MHz signals simultaneously. Our result shows 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 mean – 3.0 ms and geometric mean – 1.8 ms, ranging from 0.3 to 21.7 ms. This study is consistent with the latest finding for the slow field changes in negative ground flashes where the slow field changes never start before the preliminary breakdown process.

    Keywords
    Positive cloud-to-ground lightning flashes, Initiation position, slow field changes, close ground flashes, preliminary breakdown process
    National Category
    Other Electrical Engineering, Electronic Engineering, Information Engineering
    Research subject
    Engineering Science with specialization in Atmospheric Discharges
    Identifiers
    urn:nbn:se:uu:diva-222826 (URN)
    Funder
    Swedish Research Council, 621-2006-4299Swedish Foundation for Strategic Research , IG2004–2031
    Available from: 2014-04-15 Created: 2014-04-14 Last updated: 2017-11-09Bibliographically approved
    4. Negative cloud-to-ground lightning flashes in Malaysia
    Open this publication in new window or tab >>Negative cloud-to-ground lightning flashes in Malaysia
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    2014 (English)In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 108, p. 61-67Article in journal (Refereed) Published
    Abstract [en]

    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.

    Keywords
    Negative cloud-to-ground lightning flashes, Number of strokes per flash and interstroke interval
    National Category
    Natural Sciences Engineering and Technology
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-221965 (URN)10.1016/j.jastp.2013.12.001 (DOI)000331684900007 ()
    Available from: 2014-04-10 Created: 2014-04-07 Last updated: 2017-12-05Bibliographically approved
    5. On the characteristics of positive lightning ground flashes in Sweden
    Open this publication in new window or tab >>On the characteristics of positive lightning ground flashes in Sweden
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    2016 (English)In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 138, p. 106-111Article in journal (Refereed) Published
    Abstract [en]

    In this study the stroke characteristics of positive cloud-to-ground flashes in Sweden were obtained from the electric field records measured from 14 thunderstorms. The electric fields were measured with nanosecond resolution. Together with the fast and the slow electric field records, the narrowband radiation field at 3 and 30 MHz signals were also measured simultaneously. Out of a total of 107 flashes, 30 flashes had two strokes, 7 had three strokes and 3 flashes had four strokes. The arithmetic and geometric means of the interstroke intervals were found to be 116 and 70 ms, respectively. The arithmetic and geometric mean ratio between the peak electric field of the Subsequent Return Stroke (SRS) and the first Return Stroke (RS) were 0.48 and 0.36, respectively. Of the 40 positive multiple-stroke ground flashes, 5% have at least one SRS with field peak higher than the first RS. The percentage of SRS with field peaks greater than the first RS was 6%. In our best of our knowledge, this is the first time a large sample of positive return strokes in Sweden was analysed. It was found to be statistically more significant than the previous studies.

    Keywords
    Lightning flashes, Positive ground flashes, Positive return strokes, Electromagnetic fields
    National Category
    Meteorology and Atmospheric Sciences Engineering and Technology
    Research subject
    Engineering Science with specialization in Atmospheric Discharges
    Identifiers
    urn:nbn:se:uu:diva-274994 (URN)10.1016/j.jastp.2015.12.014 (DOI)000370769900011 ()
    Funder
    Swedish Research Council, 621-2006-4299
    Available from: 2016-01-27 Created: 2016-01-27 Last updated: 2017-11-30Bibliographically approved
    6. Comparative Study on Preliminary Breakdown Pulse Trains Observed in Malaysia and Florida
    Open this publication in new window or tab >>Comparative Study on Preliminary Breakdown Pulse Trains Observed in Malaysia and Florida
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    2010 (English)Conference paper, Published paper (Refereed)
    Place, publisher, year, edition, pages
    Cagliary, Italy: , 2010
    National Category
    Engineering and Technology
    Research subject
    Engineering Science with specialization in Atmospheric Discharges
    Identifiers
    urn:nbn:se:uu:diva-140393 (URN)
    Conference
    30TH International Conference on Lightning Protection, ICLP
    Available from: 2011-01-05 Created: 2011-01-05 Last updated: 2018-05-28
    7. The first electric field pulse of cloud and cloud-to-ground lightning discharges
    Open this publication in new window or tab >>The first electric field pulse of cloud and cloud-to-ground lightning discharges
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    2010 (English)In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 72, no 2-3, p. 143-150Article in journal (Refereed) Published
    Abstract [en]

    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.

    Keywords
    Cloud discharges, Electromagnetic field, Lightning, Electric field pulses
    National Category
    Meteorology and Atmospheric Sciences Engineering and Technology
    Research subject
    Engineering Science with specialization in Atmospheric Discharges
    Identifiers
    urn:nbn:se:uu:diva-140337 (URN)10.1016/j.jastp.2009.11.001 (DOI)
    Available from: 2011-01-05 Created: 2011-01-05 Last updated: 2017-12-11
    8. Radiation Field Spectra of Long-duration Cloud Flashes
    Open this publication in new window or tab >>Radiation Field Spectra of Long-duration Cloud Flashes
    (English)In: IEEE transactions on electromagnetic compatibility (Print), ISSN 0018-9375, E-ISSN 1558-187XArticle in journal (Refereed) Submitted
    Abstract [en]

    The radiation electric fields produced by long-duration cloud flashes have been Fourier analyzed to determined the frequency spectrum in the range of 10 kHz to 10 MHz. The flashes were recorded within a distance of less than 20 km. The spectrum was normalized to 50 km distance and it shows a f-1 dependence within the entire frequency range.

    Identifiers
    urn:nbn:se:uu:diva-150952 (URN)
    Available from: 2011-04-08 Created: 2011-04-08 Last updated: 2017-12-11
    9. Characteristics of narrow bipolar pulses observed in Malaysia
    Open this publication in new window or tab >>Characteristics of narrow bipolar pulses observed in Malaysia
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    2010 (English)In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 72, no 5-6, p. 534-540Article in journal (Refereed) Published
    Abstract [en]

    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.

    Keywords
    Narrow bipolar pulses, Lightning, Cloud discharges, Electric field
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-137067 (URN)10.1016/j.jastp.2010.02.006 (DOI)000276428600020 ()
    Available from: 2010-12-15 Created: 2010-12-15 Last updated: 2017-12-11Bibliographically approved
    10. Some features of electric field waveform of Narrow Bipolar Pulses
    Open this publication in new window or tab >>Some features of electric field waveform of Narrow Bipolar Pulses
    (English)In: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895Article in journal (Refereed) Submitted
    Abstract [en]

    Narrow Bipolar Pulses (NBPs) are generated by intra-cloud discharge processes and they are of interest due to their strong broadband and high frequency (HF) emissions. In this study, we present some features of electric field waveform of NBPs which have not been reported in the literature.  The HF emission was observed to begin simultaneously with the onset of NBPs indicating no streamers or stepped-leader process was taking place before the initiation of NBPs. The electric field waveforms of NBPs were characterized by many fine peaks embedded intermittently on the rising and decaying edge of NBPs suggesting that some small scale electrical discharges were involved during the formation of NBPs.

     

    Identifiers
    urn:nbn:se:uu:diva-150953 (URN)
    Available from: 2011-04-08 Created: 2011-04-08 Last updated: 2017-12-11
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