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Cooray, Vernon
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Publications (10 of 328) Show all publications
Cooray, V. & Cooray, G. (2019). A Novel Interpretation of the Electromagnetic Fields of Lightning Return Strokes. Atmosphere, 10(1), Article ID 22.
Open this publication in new window or tab >>A Novel Interpretation of the Electromagnetic Fields of Lightning Return Strokes
2019 (English)In: Atmosphere, ISSN 2073-4433, E-ISSN 2073-4433, Vol. 10, no 1, article id 22Article in journal (Refereed) Published
Abstract [en]

Electric and/or magnetic fields are generated by stationary charges, uniformly moving charges and accelerating charges. These field components are described in the literature as static fields, velocity fields (or generalized Coulomb field) and radiation fields (or acceleration fields), respectively. In the literature, the electromagnetic fields generated by lightning return strokes are presented using the field components associated with short dipoles, and in this description the one-to-one association of the electromagnetic field terms with the physical process that gives rise to them is lost. In this paper, we have derived expressions for the electromagnetic fields using field equations associated with accelerating (and moving) charges and separated the resulting fields into static, velocity and radiation fields. The results illustrate how the radiation fields emanating from the lightning channel give rise to field terms varying as <mml:semantics>1/r</mml:semantics> and <mml:semantics>1/r2</mml:semantics>, the velocity fields generating field terms varying as <mml:semantics>1/r2</mml:semantics>, and the static fields generating field components varying as <mml:semantics>1/r2</mml:semantics> and <mml:semantics>1/r3</mml:semantics>. These field components depend explicitly on the speed of propagation of the current pulse. However, the total field does not depend explicitly on the speed of propagation of the current pulse. It is shown that these field components can be combined to generate the field components pertinent to the dipole technique. However, in this conversion process the connection of the field components to the physical processes taking place at the source that generate these fields (i.e., static charges, uniformly moving charges and accelerating charges) is lost.

Place, publisher, year, edition, pages
MDPI, 2019
Keywords
Electromagnetic fields, return strokes, dipole fields, accelerating charges, radiation fields, static fields, velocity fields
National Category
Mathematical Analysis
Identifiers
urn:nbn:se:uu:diva-378742 (URN)10.3390/atmos10010022 (DOI)000459133000022 ()
Funder
Swedish Research Council, VR-2015-05026
Available from: 2019-03-11 Created: 2019-03-11 Last updated: 2019-03-11Bibliographically approved
Sabri, M. H., Ahmad, M. R., Esa, M. R., Periannan, D., York, S. B., Mohammad, S. A., . . . Yahaya, M. P. (2019). Environmental Analysis of Quasi-Static Electric Field Changes of Tropical Lightning Flashes. Ekoloji, 28(107), 373-378, Article ID UNSP e107013.
Open this publication in new window or tab >>Environmental Analysis of Quasi-Static Electric Field Changes of Tropical Lightning Flashes
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2019 (English)In: Ekoloji, ISSN 1300-1361, Vol. 28, no 107, p. 373-378, article id UNSP e107013Article in journal (Refereed) Published
Abstract [en]

The environmental conditions leading to the bouncing-wave discharge and the subsequent electron beam remain to be investigated in more detailed future studies. The analysis of quasi-static initial electric field changes (IECs) were found at the beginning of all 24 lightning flashes detected within reversal distance (22 Negative Cloud-to-Ground (–CG) and 2 normal Intra-Cloud (IC) flashes) in a tropical storm on June 15th, 2017 close to our station in Malacca, Malaysia (2.314077° N, 102.318282° E). The IECs durations averaged 4.28 ms for –CG flashes (range 1.48 to 9.45 ms) and averaged 11.30 ms for normal ICs flashes (range 7.24 to 15.35 ms). In comparison to Florida storms, the duration of IECs for –CG and IC flashes were 0.18 ms (range 0.08 to 0.33 ms) and 1.53 ms (range 0.18 to 5.70 ms), respectively. Moreover, the magnitudes of E-change for tropical thunderstorm were 0.13 V/m (range 0.03 to 0.44 V/m) for –CG flashes and -0.20 V/m (range -0.13 to -0.27 V/m) for IC flashes. The E-change magnitudes of tropical flashes are significantly larger than Florida flashes.

Keywords
breakdown pulse, cloud to ground flash, intra-cloud flash, lightning initiation, quasi-static electric field, environmental factors
National Category
Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:uu:diva-381389 (URN)000461678300045 ()
Available from: 2019-04-09 Created: 2019-04-09 Last updated: 2019-04-09Bibliographically approved
Rahman, M., Hettiarachchi, P., Cooray, V., Dwyer, J., Rakov, V. & Rassoul, H. (2019). Observations of X-rays from Laboratory Sparks in Air at Atmospheric Pressure under Negative Switching Impulse Voltages. Atmosphere, 10(4)
Open this publication in new window or tab >>Observations of X-rays from Laboratory Sparks in Air at Atmospheric Pressure under Negative Switching Impulse Voltages
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2019 (English)In: Atmosphere, ISSN 2073-4433, E-ISSN 2073-4433, Vol. 10, no 4Article in journal (Refereed) Published
National Category
Meteorology and Atmospheric Sciences
Research subject
Engineering Science with specialization in Atmospheric Discharges
Identifiers
urn:nbn:se:uu:diva-338135 (URN)10.3390/atmos10040169 (DOI)
Funder
The Swedish Foundation for International Cooperation in Research and Higher Education (STINT), IG2004-2031Swedish Research Council, 621-2009-2697Swedish Research Council, 621-2006-4299Swedish Research Council, 621-2012-3300
Available from: 2018-01-08 Created: 2018-01-08 Last updated: 2019-04-01
He, L., Azadifar, M., Rachidi, F., Rubinstein, M., Rakov, V. A., Cooray, V., . . . Xing, H. (2018). An Analysis of Current and Electric Field Pulses Associated With Upward Negative Lightning Flashes Initiated from the Santis Tower. Journal of Geophysical Research - Atmospheres, 123(8), 4045-4059
Open this publication in new window or tab >>An Analysis of Current and Electric Field Pulses Associated With Upward Negative Lightning Flashes Initiated from the Santis Tower
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2018 (English)In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 123, no 8, p. 4045-4059Article in journal (Refereed) Published
Abstract [en]

We present a study on the characteristics of current and electric field pulses associated with upward lightning flashes initiated from the instrumented Santis Tower in Switzerland. The electric field was measured 15km from the tower. Upward flashes always begin with the initial stage composed of the upward-leader phase and the initial-continuous-current (ICC) phase. Four types of current pulses are identified and analyzed in the paper: (1) return-stroke pulses, which occur after the extinction of the ICC and are preceded by essentially no-current time intervals; (2) mixed-mode ICC pulses, defined as fast pulses superimposed on the ICC, which have characteristics very similar to those of return strokes and are believed to be associated with the reactivation of a decayed branch or the connection of a newly created channel to the ICC-carrying channel at relatively small junction heights; (3) classical M-component pulses superimposed on the continuing current following some return strokes; and (4) M-component-type ICC pulses, presumably associated with the reactivation of a decayed branch or the connection of a newly created channel to the ICC-carrying channel at relatively large junction heights. We consider a data set consisting of 9 return-stroke pulses, 70 mixed-mode ICC pulses, 11 classical M-component pulses, and 19 M-component-type ICC pulses (a total of 109 pulses). The salient characteristics of the current and field waveforms are analyzed. A new criterion is proposed to distinguish between mixed-mode and M-component-type pulses, which is based on the current waveform features. The characteristics of M-component-type pulses during the initial stage are found to be similar to those of classical M-component pulses occurring during the continuing current after some return strokes. It is also found that about 41% of mixed-mode ICC pulses were preceded by microsecond-scale pulses occurring in electric field records some hundreds of microseconds prior to the onset of the current, very similar to microsecond-scale electric field pulses observed for M-component-type ICC pulses and which can be attributed to the junction of an in-cloud leader channel to the current-carrying channel to ground. Classical M-component pulses and M-component-type ICC pulses tend to have larger risetimes ranging from 6.3 to 430s. On the other hand, return-stroke pulses and mixed-mode ICC pulses have current risetimes ranging from 0.5 to 28s. Finally, our data suggest that the 8-s criterion for the current risetime proposed by Flache et al. is a reasonable tool to distinguish between return strokes and classical M-components. However, mixed-mode ICC pulses superimposed on the ICC can sometimes have considerably longer risetimes, up to about 28s, as observed in this study.

Keywords
lightning, upward lightning, return stroke, tall structures, charge transfer mode, lightning electric field
National Category
Meteorology and Atmospheric Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-357584 (URN)10.1029/2018JD028295 (DOI)000433071200013 ()
Funder
EU, Horizon 2020, 737033-LLR
Available from: 2018-08-17 Created: 2018-08-17 Last updated: 2018-08-20Bibliographically approved
Perera, C., Fernando, M. & Cooray, V. (2018). Analysis of Channel Tortuosity using 8 m Long Laboratory Sparks. In: : . Paper presented at 34th International Conference on Lightning Protection, September 2 - September 7, 2018,Rzeszow, Poland.
Open this publication in new window or tab >>Analysis of Channel Tortuosity using 8 m Long Laboratory Sparks
2018 (English)Conference paper, Published paper (Refereed)
National Category
Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:uu:diva-368795 (URN)
Conference
34th International Conference on Lightning Protection, September 2 - September 7, 2018,Rzeszow, Poland
Available from: 2018-12-07 Created: 2018-12-07 Last updated: 2019-03-06Bibliographically approved
Abegunawardana, S., Bodhika, J. A., Nanayakkara, S., Sonnadara, U., Fernando, M. & Cooray, V. (2018). Audible Frequency Analysis of Ground Flashes. In: : . Paper presented at 34th International Conference on Lightning Protection, September 2 - Friday, September 7, 2018, Rzeszow, Poland.
Open this publication in new window or tab >>Audible Frequency Analysis of Ground Flashes
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2018 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Thunder signatures categorized into three types based on peak pressure and variation in fundamental frequency, have been studied by using acoustic spectrum of thunder. S-transformation has been used to estimate the dominant frequency variation around the peak pressure. The mean fundamental frequencies of type 3 ground and cloud flashes are 160 Hz and 98 Hz respectively. The mean frequencies of type 2 ground and cloud flashes are 108 Hz and 82 Hz respectively.

National Category
Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:uu:diva-368747 (URN)
Conference
34th International Conference on Lightning Protection, September 2 - Friday, September 7, 2018, Rzeszow, Poland
Available from: 2018-12-07 Created: 2018-12-07 Last updated: 2019-03-06Bibliographically approved
Bodhika, J. A., Dharmarathna, W., Fernando, M. & Cooray, V. (2018). Characteristics of thunder pertinent to tropical lightning. In: : . Paper presented at 34th International Conference on Lightning Protection, 2-7 September, 2018, Rzeszow, Poland.
Open this publication in new window or tab >>Characteristics of thunder pertinent to tropical lightning
2018 (English)Conference paper, Published paper (Refereed)
National Category
Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:uu:diva-368792 (URN)
Conference
34th International Conference on Lightning Protection, 2-7 September, 2018, Rzeszow, Poland
Available from: 2018-12-07 Created: 2018-12-07 Last updated: 2019-03-06Bibliographically approved
Cooray, V., Fernando, M., Gunasekara, L. & Nanayakkara, S. (2018). Effects of Propagation of Narrow Bipolar Pulses, Generated by Compact Cloud Discharges, over Finitely Conducting Ground. Atmosphere, 9(5), Article ID 193.
Open this publication in new window or tab >>Effects of Propagation of Narrow Bipolar Pulses, Generated by Compact Cloud Discharges, over Finitely Conducting Ground
2018 (English)In: Atmosphere, ISSN 2073-4433, E-ISSN 2073-4433, Vol. 9, no 5, article id 193Article in journal (Refereed) Published
Abstract [en]

Propagation effects on the narrow bipolar pulses (NBPs) or the radiation fields generated by compact cloud discharges as they propagate over finitely conducting ground are presented. The results were obtained using a sample of NBPs recorded with high time resolution from close thunderstorms in Sri Lanka. The results show that the peak amplitude and the temporal features such as the full width at half maximum (FWHM), zero-crossing time, and the time derivative of NBPs can be significantly distorted by propagation effects. For this reason, the study of peak amplitudes and temporal features of NBPs and the remote sensing of current parameters of compact cloud discharges should be conducted using NBPs recorded under conditions where the propagation effects are minimal.

Place, publisher, year, edition, pages
MDPI, 2018
Keywords
compact cloud discharges, narrow bipolar pulses, propagation effects, finitely conducting ground
National Category
Meteorology and Atmospheric Sciences Communication Systems
Identifiers
urn:nbn:se:uu:diva-358099 (URN)10.3390/atmos9050193 (DOI)000435190300036 ()
Funder
Swedish Research Council, 621-2003-3465Swedish Research Council, 621-2006-4299
Available from: 2018-08-24 Created: 2018-08-24 Last updated: 2018-08-24Bibliographically approved
Gunasekara, T. A., Fernando, M., Sonnadara, U. & Cooray, V. (2018). Horizontal electric fields of lightning return strokes and narrow bipolar pulses observed in Sri Lanka. Journal of Atmospheric and Solar-Terrestrial Physics, 173, 57-65
Open this publication in new window or tab >>Horizontal electric fields of lightning return strokes and narrow bipolar pulses observed in Sri Lanka
2018 (English)In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 173, p. 57-65Article in journal (Refereed) Published
Abstract [en]

Simultaneous measurement of both vertical and horizontal electric field signatures of lightning was carried out in an elevated location in Colombo, Sri Lanka. The experimental setup used in this work was similar to an earlier study carried out by a different group in the late 1980s. To our knowledge, this is the first instance that such a study is conducted in this region. Data were acquired during the active months (April-May) of the southwest monsoon period in 2014. Lightning flashes from the most active thunderstorm was analyzed by selecting 65 Return Strokes (RS), 50 Negative Narrow Bipolar Pulses (NNBP) and 40 Positive Narrow Bipolar Pulses (PNBP). The wave shapes were initially validated against results of a previous study and subsequently via a theoretical method as well. Since the direction and the distance information was not available, rather than the amplitudes, ratios of the peak amplitudes of vertical electric field (Ev) and corresponding horizontal electric field (Eh) were compared. The average ratio for the return stroke was 0.024 +/- 0.008. The same for the NNBP was 0.041 +/- 0.004. The PNBP had a ratio of 0.031 +/- 0.006. The average 10%-90% rise times (Tr) for Ev for RS, NNBP and PNBP was 2.124 +/- 1.088 mu s, 0.734 +/- 0.077 is and 1.141 +/- 0.311 mu s respectively. The Tr values for Eh for RS, NNBP and PNBP were 1.865 +/- 1.200 mu s, 0.538 +/- 0.061 mu s and 1.086 +/- 0.423 mu s.

National Category
Meteorology and Atmospheric Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-357677 (URN)10.1016/j.jastp.2018.04.010 (DOI)000433653800007 ()
Available from: 2018-08-20 Created: 2018-08-20 Last updated: 2018-08-23Bibliographically approved
Sapumanage, N., Nanayakkara, S., Abegunawardena, S., Fernando, M. & Cooray, V. (2018). How physical attributes of transient voltages limits the efficiency of SPD array. In: : . Paper presented at 34th International Conference on Lightning Protection,2-7 September, 2018, Rzeszow, Poland.
Open this publication in new window or tab >>How physical attributes of transient voltages limits the efficiency of SPD array
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2018 (English)Conference paper, Published paper (Refereed)
National Category
Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:uu:diva-368801 (URN)
Conference
34th International Conference on Lightning Protection,2-7 September, 2018, Rzeszow, Poland
Available from: 2018-12-07 Created: 2018-12-07 Last updated: 2019-03-07Bibliographically approved
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