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Cooray, Vernon
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Publications (10 of 309) Show all publications
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
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
Diaz, O., Cooray, V. & Arevalo, L. (2018). Numerical Modeling of Electrical Discharges in Long Air Gaps Tested With Positive Switching Impulses. IEEE Transactions on Plasma Science, 46(3), 611-621
Open this publication in new window or tab >>Numerical Modeling of Electrical Discharges in Long Air Gaps Tested With Positive Switching Impulses
2018 (English)In: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 46, no 3, p. 611-621Article in journal (Refereed) Published
Abstract [en]

The numerical modeling of electrical discharges occurring in atmospheric air has been in continuous development during the past decades in different fields, such as high-voltage techniques and lightning protection. Different methodologies have been proposed to represent the physical phenomena taking place at a single full discharge event, departing both from experimental and theoretical approaches. The implementation of these methodologies in numerical routines combined with the use of numerical methods to determine the electric potential distribution permits the creation of models whose predictions closely agree with the real case situations, where electrode arrangements might have nonsymmetric geometries. In this paper, we present an improved version of a simulation methodology for representing electrical discharges in long air gaps. This simulation methodology includes new elements like: 1) the 3-D leader channel tortuosity based on laboratory experimental measurements and 2) two new methods for the estimation of the electric charge contained in the so-called leader-corona region based on the electrostatic potential of fictitious potential rings representing the active region in front of the leader tip. Results from the simulation were compared with experimental records and a reasonably good agreement is found between them.

Keywords
Gas discharge, electric breakdown, EHV insulation, UHV insulation
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Atmospheric Discharges
Identifiers
urn:nbn:se:uu:diva-298356 (URN)10.1109/TPS.2018.2802039 (DOI)000427127000022 ()
Note

Title in thesis list of papers: Numerical modeling of long air gaps tested with positive switching impulses

Available from: 2016-07-04 Created: 2016-07-04 Last updated: 2018-05-28Bibliographically approved
Vayanganie, S. P., Fernando, M., Sonnadara, U., Cooray, V. & Perera, C. (2018). Optical observations of electrical activity in cloud discharges. Journal of Atmospheric and Solar-Terrestrial Physics, 172, 24-32
Open this publication in new window or tab >>Optical observations of electrical activity in cloud discharges
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2018 (English)In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 172, p. 24-32Article in journal (Refereed) Published
Abstract [en]

Temporal variation of the luminosity of seven natural cloud-to-cloud lightning channels were studied, and results were presented. They were recorded by using a high-speed video camera with the speed of 5000 fps (frames per second) and the pixel resolution of 512 x 512 in three locations in Sri Lanka in the tropics. Luminosity variation of the channel with time was obtained by analyzing the image sequences. Recorded video frames together with the luminosity variation were studied to understand the cloud discharge process. Image analysis techniques also used to understand the characteristics of channels. Cloud flashes show more luminosity variability than ground flashes. Most of the time it starts with a leader which do not have stepping process. Channel width and standard deviation of intensity variation across the channel for each cloud flashes was obtained. Brightness variation across the channel shows a Gaussian distribution. The average time duration of the cloud flashes which start with non stepped leader was 180.83 ms. Identified characteristics are matched with the existing models to understand the process of cloud flashes. The fact that cloud discharges are not confined to a single process have been further confirmed from this study. The observations show that cloud flash is a basic lightning discharge which transfers charge between two charge centers without using one specific mechanism.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2018
Keywords
Cloud lightning, High-speed photography, Luminosity variation
National Category
Meteorology and Atmospheric Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-356441 (URN)10.1016/j.jastp.2018.03.007 (DOI)000432501500003 ()
Available from: 2018-07-31 Created: 2018-07-31 Last updated: 2018-08-15Bibliographically approved
Cooray, V. (2018). Origin of the Fine Scale Tortuosity in Sparks and Lightning Channels. Atmosphere, 9(6), Article ID 205.
Open this publication in new window or tab >>Origin of the Fine Scale Tortuosity in Sparks and Lightning Channels
2018 (English)In: Atmosphere, ISSN 2073-4433, E-ISSN 2073-4433, Vol. 9, no 6, article id 205Article in journal (Refereed) Published
Abstract [en]

The physical reason for the small-scale tortuosity observed in sparks and lightning channels is unknown at present. In this paper, it is suggested that the small-scale tortuosity of the discharge channels is caused by the natural tendency for subsequent leader streamer bursts to avoid each other but at the same time to align as much as possible along the direction of the background electric field. This process will give rise to a discharge channel that re-orients in space during each streamer burst creating the small scale tortuosity.

Place, publisher, year, edition, pages
MDPI, 2018
Keywords
lightning, spark discharges, tortuosity, streamer bursts, leaders
National Category
Meteorology and Atmospheric Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-358701 (URN)10.3390/atmos9060205 (DOI)000436271900003 ()
Available from: 2018-09-03 Created: 2018-09-03 Last updated: 2018-09-06Bibliographically approved
Cooray, V. (2018). The Similarity of the Action of Franklin and ESE Lightning Rods under Natural Conditions. Atmosphere, 9(6), Article ID 225.
Open this publication in new window or tab >>The Similarity of the Action of Franklin and ESE Lightning Rods under Natural Conditions
2018 (English)In: Atmosphere, ISSN 2073-4433, E-ISSN 2073-4433, Vol. 9, no 6, article id 225Article in journal (Refereed) Published
Abstract [en]

In the lightning rods categorized as Early Streamer Emission (ESE) types, an intermittent voltage impulse is applied to the lightning rod to modulate the electric field at its tip in an attempt to speed up the initiation of a connecting leader from the lightning rod when it is under the influence of a stepped leader moving down from the cloud. In this paper, it is shown that, due to the stepping nature of the stepped leader, there is a natural modulation of the electric field at the tip of any lightning rod exposed to the lightning stepped leaders and this modulation is much more intense than any artificial modulation that is possible under practical conditions. Based on the results, it is concluded that artificial modulation of the electric field at the tip of lightning rods by applying voltage pulses is an unnecessary endeavor because the nature itself has endowed the tip of the lightning rod with a modulating electric field. Therefore, as far as the effectiveness of artificial modulation of the tip electric field is concerned, there could be no difference in the lightning attachment efficiency between ESE and Franklin lightning rods.

Place, publisher, year, edition, pages
MDPI, 2018
Keywords
Franklin lightning rod, Early Streamer Emission, ESE lightning rod, lightning attachment
National Category
Meteorology and Atmospheric Sciences Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-358700 (URN)10.3390/atmos9060225 (DOI)000436271900023 ()
Available from: 2018-09-03 Created: 2018-09-03 Last updated: 2018-09-03Bibliographically approved
Hettiarachchi, P., Cooray, V., Diendorfer, G., Pichler, H., Dwyer, J. & Rahman, M. (2018). X-ray observations at Gaisberg Tower. Atmosphere, 9(1), Article ID 20.
Open this publication in new window or tab >>X-ray observations at Gaisberg Tower
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2018 (English)In: Atmosphere, ISSN 2073-4433, E-ISSN 2073-4433, Vol. 9, no 1, article id 20Article in journal (Refereed) Published
Abstract [en]

We report the occurrence of X-rays at ground level due to cloud-to-ground flashes of upward initiated lightning from Gaisberg Tower in Austria which is located at a 1300 m altitude.  This is the first time that the X-rays from upward lightning from a tower top located in high altitude is observed. Measurement was carried out using scintillation detectors installed close to the tower top in two phases from 2011 to 2015. X-rays were recorded in three subsequent strokes of three flashes out of the total of 108 flashes recorded in the system during both phases. In contrast to the observations from downward natural or triggered lightning, X-rays were observed only within 10 µs before the subsequent return stroke. This shows that X-rays were emitted when the dart leader is in the vicinity of the tower top and hence during the most intense phase of the dart leader. Both the detected energy and the fluence of X-rays are far lower compared to X-rays from downward natural or rocket-triggered lightning. In addition to above 108 flashes, an interesting observation of X-rays produced by a nearby downward flash is also presented. The shorter dart-leader channels length in Gaisberg is suggested as a possible cause of this apparently weaker X-ray production.

National Category
Meteorology and Atmospheric Sciences Engineering and Technology
Research subject
Engineering Science with specialization in Atmospheric Discharges
Identifiers
urn:nbn:se:uu:diva-338132 (URN)10.3390/atmos9010020 (DOI)000424095100019 ()
Funder
Swedish Research Council, 2015-05026
Available from: 2018-01-08 Created: 2018-01-08 Last updated: 2018-03-19Bibliographically approved
Cooray, V. & Rachidi, F. (2017). Advances in lightning research. Journal of Atmospheric and Solar-Terrestrial Physics, 154, 181-181
Open this publication in new window or tab >>Advances in lightning research
2017 (English)In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 154, p. 181-181Article in journal, Editorial material (Refereed) Published
Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2017
National Category
Earth and Related Environmental Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-320996 (URN)10.1016/j.jastp.2016.10.014 (DOI)000395952000017 ()
Available from: 2017-04-28 Created: 2017-04-28 Last updated: 2017-12-29Bibliographically approved
Lobato, A., Cooray, V. & Arevalo, L. (2017). Attractive Zone of Lightning Rods Evaluated with a Leader Progression Model in a Common Building in Brazil. In: 2017 INTERNATIONAL SYMPOSIUM ON LIGHTNING PROTECTION (XIV SIPDA): . Paper presented at 2017 International Symposium on Lightning Protection (XIV SIPDA, 2-6 Oct. 2017,Natal, Brazil. (pp. 380-388). IEEE
Open this publication in new window or tab >>Attractive Zone of Lightning Rods Evaluated with a Leader Progression Model in a Common Building in Brazil
2017 (English)In: 2017 INTERNATIONAL SYMPOSIUM ON LIGHTNING PROTECTION (XIV SIPDA), IEEE, 2017, p. 380-388Conference paper, Published paper (Refereed)
Abstract [en]

Modeling the lightning attachment process is required on any method to design the air-termination elements of a lightning protection system. An attachment model that adopts the leader progression concept is used to evaluate the three-dimensional attractive zone of a lightning rod on a common 54-m tall building in Sao Paulo, Brazil. Electric field and scalar potential distributions are calculated numerically with a finite element method. The result is compared with the interception volume predicted by the electro-geometric model, as applied by the rolling sphere method. The results show that the electrogeometric theory underestimates the striking distance and the attractive radius. Moreover, in the presence of upward connecting leaders, the striking distance varies according to the field enhancement on the geometry of the structure and the lateral displacement of the stepped leader. The simulated propagated distances and speeds of the downward and upward leaders are compared with a recently published high-speed video analysis of a natural lightning attachment case observed on the evaluated lightning rod. A reasonable agreement between the simulated and measured leader characteristics has been found.

Place, publisher, year, edition, pages
IEEE, 2017
Keywords
leader progression model, lightning protection, lightning rod, finite element method
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-354386 (URN)10.1109/SIPDA.2017.8116956 (DOI)000427288000066 ()978-1-5090-6054-2 (ISBN)978-1-5090-6053-5 (ISBN)978-1-5090-6052-8 (ISBN)
Conference
2017 International Symposium on Lightning Protection (XIV SIPDA, 2-6 Oct. 2017,Natal, Brazil.
Available from: 2018-06-29 Created: 2018-06-29 Last updated: 2018-06-29Bibliographically approved
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