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Ismail, Mohd Muzafar
Alternative names
Publications (9 of 9) Show all publications
Johari, D., Cooray, V., Rahman, M., Hettiarachchi, P. & Ismail, M. M. (2017). Characteristics of leader pulses in positive ground flashes in Sweden. Electric power systems research, 153, 3-9
Open this publication in new window or tab >>Characteristics of leader pulses in positive ground flashes in Sweden
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2017 (English)In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 153, p. 3-9Article in journal (Refereed) Published
Abstract [en]

This paper presents the characteristics of the electric field pulses observed during leader propagation in positive ground flashes. We analysed in detail the electric field changes occurring just before the first return stroke in 51 positive ground flashes during 2014 summer thunderstorms in Uppsala, Sweden. Pronounced leader pulses (having the same polarity as the return stroke) were observed in 22% of the cases. They were observed to occur within 1.4 ms before the first return stroke. Interpulse duration ranged from 13.3 to 50.3 μs with a mean value of 24.7 μs. The peak amplitude of the leader pulses relative to the return stroke peak ranged from 2.7 to 17.8%. The presence of these pulses shows that the leaders propagate in a stepped manner. Based on the leader pulses’ time of initiation and average speed of the leader, the distance travelled by the leader was also estimated. One case of positive ground flash preceded by opposite polarity leader pulses just before the return stroke is also reported. To the best of our knowledge, this is the first time that such a case in positive ground flashes is reported. We suggest that these opposite polarity leader pulses are due to the negatively-charged leader branch of a bi-directional leader inside the cloud that propagates towards observation point.

National Category
Meteorology and Atmospheric Sciences Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Atmospheric Discharges
Identifiers
urn:nbn:se:uu:diva-293059 (URN)10.1016/j.epsr.2016.11.026 (DOI)000413380500002 ()
Available from: 2016-05-11 Created: 2016-05-11 Last updated: 2019-07-16Bibliographically approved
Johari, D., Cooray, V., Rahman, M., Hettiarachchi, P. & Ismail, M. M. (2017). Features of the First and Subsequent Return Strokes in Positive Ground Flashes based on Electric Field Measurements. Electric power systems research, 150, 55-62
Open this publication in new window or tab >>Features of the First and Subsequent Return Strokes in Positive Ground Flashes based on Electric Field Measurements
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2017 (English)In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 150, p. 55-62Article in journal (Refereed) Published
Abstract [en]

This paper presents the characteristics of the electric fields produced by the first and the subsequent return strokes observed in positive ground flashes in Sweden. Fifty one positive ground flashes containing 60 return strokes recorded during 2014 summer thunderstorms were analyzed. In our analysis, only 12% of the cases were multiple-stroke while 88% were single-stroke. On average, the number of strokes per flash was 1.20 and the highest number of strokes per flash recorded was four. The geometric mean (GM) value of the interstroke interval was 60 ms while the distance between the first and the subsequent strokes ranged between 4.9 and 46.4km. We found that the average duration of the subsequent strokes parameters were smaller than that of the first strokes. For the first strokes, the GM values of the slow front duration, the fast transition 10-to-90% risetime, the zero crossing time, the zero-to-peak risetime and the 10-to-90% risetime were 8.7 mu s, 1.4 mu s, 29 mu s, 11 mu s and 5.7 mu s, respectively while for the subsequent strokes, the values were 4.0 mu s 0.91 mu s, 11 mu s 5.8 mu s and 3.2 mu s, respectively. Possible reasons for the shorter duration of the subsequent return strokes parameters were discussed.

National Category
Meteorology and Atmospheric Sciences Engineering and Technology
Research subject
Engineering Science with specialization in Atmospheric Discharges
Identifiers
urn:nbn:se:uu:diva-317450 (URN)10.1016/j.epsr.2017.04.031 (DOI)000403744100006 ()
Available from: 2017-03-14 Created: 2017-03-14 Last updated: 2017-10-20Bibliographically approved
Ismail, M. M., Rahman, M., Cooray, V., Fernando, M., Hettiarachchi, P. & Johari, D. (2017). On the possible origin of chaotic pulse trains in lightning flashes. Atmosphere, 8(2), Article ID 29.
Open this publication in new window or tab >>On the possible origin of chaotic pulse trains in lightning flashes
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2017 (English)In: Atmosphere, ISSN 2073-4433, E-ISSN 2073-4433, Vol. 8, no 2, article id 29Article in journal (Refereed) Published
Abstract [en]

In this study, electromagnetic field radiation bursts known as chaotic pulse trains (CPTs) and regular pulse trains (RPTs) generated by lightning flashes were analyzed. Through a numerical analysis it was found that a typical CPT could be generated by superimposing several RPTs onto each other. It is suggested that the chaotic pulse trains are created by a superposition of several regular pulse trains. Since regular pulse trains are probably created by dart or dart-stepped leaders or K-changes inside the cloud, chaotic pulse trains are caused by the superposition of electric fields caused by more than one of these leaders or K-changes propagating simultaneously. The hypothesis is supported by the fact that one can find regular pulse trains either in the beginning, middle or later stages of chaotic pulse trains.

Keywords
regular pulse train, chaotic pulse train, numerical superposition, HF radiation
National Category
Meteorology and Atmospheric Sciences Engineering and Technology
Research subject
Engineering Science with specialization in Atmospheric Discharges
Identifiers
urn:nbn:se:uu:diva-313561 (URN)10.3390/atmos8020029 (DOI)000396166200007 ()
Available from: 2017-01-20 Created: 2017-01-20 Last updated: 2017-11-29Bibliographically approved
Johari, D., Cooray, V., Rahman, M., Hettiarachchi, P. & Ismail, M. (2016). Characteristics of preliminary breakdown pulses in positive ground flashes during summer thunderstorms in Sweden. Atmosphere, 7(3), Article ID 39.
Open this publication in new window or tab >>Characteristics of preliminary breakdown pulses in positive ground flashes during summer thunderstorms in Sweden
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2016 (English)In: Atmosphere, ISSN 2073-4433, E-ISSN 2073-4433, Vol. 7, no 3, article id 39Article in journal (Refereed) Published
Abstract [en]

This paper presents the characteristics of the preliminary breakdown pulses (PBP) in 51 positive ground flashes recorded during 2014 summer thunderstorms in Sweden. Electric field measurements were conducted remotely using a broadband antenna system (up to 100 MHz) for a recording length of 1 s with 200 ms trigger time. In the analysis, PBP trains were observed in 86% of the cases. Based on the number of trains preceding the first return stroke, the PBP were classified into single and multiple train PBP. Characteristics of the first PBP train were determined and based on the initial polarity of the pulses, three types of PBP were identified. Characteristics of the subsequent PBP trains in the multiple train PBP were also analyzed and they were compared with the first PBP train. Based on the conceptual charge cloud configuration, we found that the inverted dipole is consistent with our observation. We also found that PBP in positive ground flashes during summer thunderstorms in Sweden are weak since the average ratios of the PBP peak to the first return stroke peak lie only between 0.21 and 0.26. Possible reasons for no detection of PBP and the different types of PBP observed were also discussed.

National Category
Meteorology and Atmospheric Sciences Engineering and Technology
Research subject
Engineering Science with specialization in Atmospheric Discharges
Identifiers
urn:nbn:se:uu:diva-280866 (URN)10.3390/atmos7030039 (DOI)000373529700002 ()
Available from: 2016-03-15 Created: 2016-03-15 Last updated: 2017-11-30Bibliographically approved
Ismail, M. M., Rahman, M., Cooray, V., Sharma, S., Hettiarachchi, P. & Johari, D. (2015). Electric field signatures in wideband, 3 MHz and 30 MHz of negative ground flashes pertinent to Swedish thunderstorms. Atmosphere, 6(12), 1904-1925
Open this publication in new window or tab >>Electric field signatures in wideband, 3 MHz and 30 MHz of negative ground flashes pertinent to Swedish thunderstorms
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2015 (English)In: Atmosphere, ISSN EISSN 2073-4433, Vol. 6, no 12, p. 1904-1925Article in journal (Refereed) Published
Abstract [en]

In this study, the electric field signatures of negative ground flashes pertinent to the Swedish thunderstorms were recorded simultaneously during the summer of 2014 using wide (up to 100 MHz) and narrow (at 3 MHz and 30 MHz as central frequencies) bandwidth antenna systems. The electric field signatures were recorded for a time duration of 250 ms. In the analysis, the whole flash was considered and a total of 98 flashes were chosen where electric field signatures of all wideband, 3 MHz and 30 MHz signals were present. It is observed that preliminary breakdown pulses are stronger radiators at 3 and 30 MHz compared to the return strokes. A comparison of our results with those of the previous studies obtained from different geographical regions clearly shows that the strength of preliminary breakdown pulses is higher in the temperate region (Sweden for instance) and is a function of latitude.

Keywords
Lightning negative ground flashes, 3 MHz and 30 MHz radiations
National Category
Meteorology and Atmospheric Sciences Engineering and Technology
Research subject
Engineering Science with specialization in Atmospheric Discharges
Identifiers
urn:nbn:se:uu:diva-268851 (URN)10.3390/atmos6121837 (DOI)000367443100004 ()
Available from: 2015-12-10 Created: 2015-12-10 Last updated: 2017-08-02Bibliographically approved
Ismail, M. M., Sharma, S. R., Cooray, V., Hettiarachchi, P., Rahman, M. & Johari, D. (2015). HF and VHF electric field radiation produced by preliminary breakdown process pertinent to Swedish thunderstorms. In: 2015 Asia-Pacific International Conference on Lightning (APL), Nagoya, Japan: . Paper presented at 2015 Asia-Pacific International Conference on Lightning (APL), Nagoya, Japan.
Open this publication in new window or tab >>HF and VHF electric field radiation produced by preliminary breakdown process pertinent to Swedish thunderstorms
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2015 (English)In: 2015 Asia-Pacific International Conference on Lightning (APL), Nagoya, Japan, 2015Conference paper, Published paper (Refereed)
National Category
Meteorology and Atmospheric Sciences Engineering and Technology
Research subject
Engineering Science with specialization in Atmospheric Discharges
Identifiers
urn:nbn:se:uu:diva-285837 (URN)
Conference
2015 Asia-Pacific International Conference on Lightning (APL), Nagoya, Japan
Available from: 2016-04-19 Created: 2016-04-19 Last updated: 2016-04-22
Ismail, M. M., Cooray, V., Hettiarachchi, P., Rahman, M., Fernando, M. & Johari, D. (2015). On the possible origin of chaotic pulse trains in lightning flashes. In: 2015 International Symposium on Lightning Protection (XIII SIPDA), Balneário Camboriú, Brazil, 28th Sept. – 2nd Oct. 2015.: . Paper presented at 2015 International Symposium on Lightning Protection (XIII SIPDA), Balneário Camboriú, Brazil, 28th Sept. – 2nd Oct. 2015. (pp. 409-412).
Open this publication in new window or tab >>On the possible origin of chaotic pulse trains in lightning flashes
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2015 (English)In: 2015 International Symposium on Lightning Protection (XIII SIPDA), Balneário Camboriú, Brazil, 28th Sept. – 2nd Oct. 2015., 2015, p. 409-412Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

it is suggested that the chaotic pulse trains observed in lightning flashes are created as a result of the superposition of several regular pulse bursts produced by dart leader type discharge processes in the cloud. The similarity between the individual pulses in both chaotic and regular pulse bursts strengthen this suggestion.

Keywords
regular pulse; chaotic pulse train; superposition
National Category
Meteorology and Atmospheric Sciences Engineering and Technology
Research subject
Engineering Science with specialization in Atmospheric Discharges
Identifiers
urn:nbn:se:uu:diva-284729 (URN)000382966700052 ()9781479987542 (ISBN)
Conference
2015 International Symposium on Lightning Protection (XIII SIPDA), Balneário Camboriú, Brazil, 28th Sept. – 2nd Oct. 2015.
Available from: 2016-04-19 Created: 2016-04-19 Last updated: 2016-10-28Bibliographically approved
Johari, D., Cooray, V., Hettiarachchi, P., Rahman, M. & Ismail, M. M. (2015). Some characteristics of leader pulses in positive cloud-to-ground flashes. In: 2015 International Symposium On Lightning Protection (Xiii SIPDA): . Paper presented at 2015 International Symposium on Lightning Protection (XIII SIPDA) (pp. 283-287).
Open this publication in new window or tab >>Some characteristics of leader pulses in positive cloud-to-ground flashes
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2015 (English)In: 2015 International Symposium On Lightning Protection (Xiii SIPDA), 2015, p. 283-287Conference paper, Published paper (Refereed)
Abstract [en]

Compared to negative ground flashes, not much is known about the characteristics of leaders in positive ground flashes. This paper presents some characteristics of the electric field pulses observed during leader propagation in positive ground flashes. We analyzed in detail the electric field changes produced by 50 positive ground flashes during 2014 summer thunderstorms in Uppsala, Sweden. Pronounced leader pulses were observed in 22% of the cases. They were observed to occur 1.4 ms or less before the first return stroke. Interpulse duration ranged from 13.3-50.3 mu s with a mean value of 24.7 mu s. The largest relative amplitude ranged from 2.7-17.8 % of the return stroke peak. No dependence of the pulses occurrence were observed with distance. However, the relative amplitude were found to decrease with distance. The presence of these pulses suggests that the leaders propagate in a stepped manner. One case of positive ground flashes preceded by negative polarity pulses just before the return stroke is also reported.

Keywords
positive ground flash; positive leader; stepped-leader
National Category
Meteorology and Atmospheric Sciences Engineering and Technology
Research subject
Engineering Science with specialization in Atmospheric Discharges
Identifiers
urn:nbn:se:uu:diva-286607 (URN)10.1109/SIPDA.2015.7339281 (DOI)000382966700050 ()9781479987542 (ISBN)
Conference
2015 International Symposium on Lightning Protection (XIII SIPDA)
Available from: 2016-04-21 Created: 2016-04-21 Last updated: 2016-10-28Bibliographically approved
Ahmad, M. R., Mohd Esa, M. R., Johari, D., Ismail, M. M. & Cooray, V. (2014). Chaotic Pulse Train in Cloud-to-Ground and Cloud Flashes of Tropical Thunderstorms. In: : . Paper presented at 2014 International Conference on Lightning Protection (ICLP), OCT 11-18, 2014, Tsinghua Univ, Shanghai, PEOPLES R CHINA (pp. 808-809). IEEE conference proceedings
Open this publication in new window or tab >>Chaotic Pulse Train in Cloud-to-Ground and Cloud Flashes of Tropical Thunderstorms
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2014 (English)Conference paper, Published 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.

Place, publisher, year, edition, pages
IEEE conference proceedings, 2014
Keywords
Chaotic pulse; Cloud flash.
National Category
Meteorology and Atmospheric Sciences Engineering and Technology
Research subject
Engineering Science with specialization in Atmospheric Discharges
Identifiers
urn:nbn:se:uu:diva-233651 (URN)000358572100152 ()978-1-4799-3544-4 (ISBN)
Conference
2014 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
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