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Cooray, Vernon
Alternative names
Publications (10 of 294) Show all publications
Hettiarachchi, P., Cooray, V., Diendorfer, G., Pichler, H., Dwyer, J. & Rahman, M. (2018). X-ray observations at Gaisberg Tower. Atmosphere, 9(1), 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, 20- p.Article 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
Research subject
Engineering Science with specialization in Atmospheric Discharges
Identifiers
urn:nbn:se:uu:diva-338132 (URN)10.3390/atmos9010020 (DOI)
Funder
Swedish Research Council, 2015-05026
Available from: 2018-01-08 Created: 2018-01-08 Last updated: 2018-01-17
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, 181-181 p.Article 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
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, 3-9 p.Article in journal (Refereed) Published
National Category
Meteorology and Atmospheric Sciences Engineering and Technology
Research subject
Engineering Science with specialization in Atmospheric Discharges
Identifiers
urn:nbn:se:uu:diva-293059 (URN)
Available from: 2016-05-11 Created: 2016-05-11 Last updated: 2017-10-20
Cooray, V. & Cooray, G. (2017). Electromagnetic fields of accelerating charges: Applications in lightning protection. Electric power systems research, 145, 234-247.
Open this publication in new window or tab >>Electromagnetic fields of accelerating charges: Applications in lightning protection
2017 (English)In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 145, 234-247 p.Article in journal (Refereed) Published
Abstract [en]

Electromagnetic fields generated by accelerating charges can be utilized to evaluate the electromagnetic fields generated by systems where moving charges and/or propagating currents are present. The technique can be used easily to evaluate the electromagnetic fields generated by systems in which propagating currents are present. This is illustrated by utilizing the equations to derive expressions for the electromagnetic fields generated by systems in which current pulses injected by lightning flashes are propagating.

Keyword
Lightning, Electromagnetic fields, Accelerating charges, Return stroke models
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-320636 (URN)10.1016/j.epsr.2016.12.013 (DOI)000395223000024 ()
Available from: 2017-08-07 Created: 2017-08-07 Last updated: 2017-08-07Bibliographically 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, 55-62 p.Article 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
Cooray, V. & Cooray, G. (2017). On the Action of the Radiation Field Generated by a Traveling-Wave Element and Its Connection to the Time Energy Uncertainty Principle, Elementary Charge and the Fine Structure Constant [Letter to the editor]. Atmosphere, 8(3), Article ID 46.
Open this publication in new window or tab >>On the Action of the Radiation Field Generated by a Traveling-Wave Element and Its Connection to the Time Energy Uncertainty Principle, Elementary Charge and the Fine Structure Constant
2017 (English)In: Atmosphere, ISSN 2073-4433, E-ISSN 2073-4433, Vol. 8, no 3, 46Article in journal, Letter (Refereed) Published
Abstract [en]

Recently, we published two papers in this journal. One of the papers dealt with the action of the radiation fields generated by a traveling-wave element and the other dealt with the momentum transferred by the same radiation fields and their connection to the time energy uncertainty principle. The traveling-wave element is defined as a conductor through which a current pulse propagates with the speed of light in free space from one end of the conductor to the other without attenuation. The goal of this letter is to combine the information provided in these two papers together and make conclusive statements concerning the connection between the energy dissipated by the radiation fields, the time energy uncertainty principle and the elementary charge. As we will show here, the results presented in these two papers, when combined together, show that the time energy uncertainty principle can be applied to the classical radiation emitted by a traveling-wave element and it results in the prediction that the smallest charge associated with the current that can be detected using radiated energy as a vehicle is on the order of the elementary charge. Based on the results, an expression for the fine structure constant is obtained. This is the first time that an order of magnitude estimation of the elementary charge based on electromagnetic radiation fields is obtained. Even though the results obtained in this paper have to be considered as order of magnitude estimations, a strict interpretation of the derived equations shows that the fine structure constant or the elementary charge may change as the size or the age of the universe increases.

Place, publisher, year, edition, pages
MDPI AG, 2017
Keyword
traveling-wave element, radiation fields, momentum, action, elementary charge, time energy uncertainty principle, fine structure constant, age of the universe
National Category
Meteorology and Atmospheric Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-321159 (URN)10.3390/atmos8030046 (DOI)000398734800004 ()
Available from: 2017-05-02 Created: 2017-05-02 Last updated: 2017-11-29Bibliographically 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, 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.

Keyword
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
Arevalo, L. & Cooray, V. (2017). Unstable Leader Inception Criteria of Atmospheric Discharges. Atmosphere, 8(9), Article ID 156.
Open this publication in new window or tab >>Unstable Leader Inception Criteria of Atmospheric Discharges
2017 (English)In: Atmosphere, ISSN 2073-4433, E-ISSN 2073-4433, Vol. 8, no 9, 156Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
MDPI AG, 2017
Keyword
electric breakdown, discharges, ionization, modeling, plasma temperature, thermal stability
National Category
Meteorology and Atmospheric Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-336485 (URN)10.3390/atmos8090156 (DOI)000411527500001 ()
Available from: 2017-12-14 Created: 2017-12-14 Last updated: 2017-12-15Bibliographically approved
Hettiarachchi, P., Rahman, M., Cooray, V. & Dwyer, J. (2017). X-rays from negative laboratory sparks in air: Influence of the anode geometry. Journal of Atmospheric and Solar-Terrestrial Physics, 154, 190-194.
Open this publication in new window or tab >>X-rays from negative laboratory sparks in air: Influence of the anode geometry
2017 (English)In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 154, 190-194 p.Article in journal (Refereed) Published
Abstract [en]

In this experimental work, the influence of the grounded anode geometry is studied on the X-ray production from the laboratory sparks in air at atmospheric pressure when a negative impulse voltage is applied to a high voltage rod which served as a cathode. The result shows that the smaller the diameter of the anode, the higher the energy of X-ray bursts. This observation can be explained by the mechanism that the encounter of negative and positive streamer fronts just before the final breakdown is the event that accelerates electrons to X-ray generating energies, but may not be the only mechanism that generates X-rays.

Keyword
X-rays, laboratory sparks, electrodes, runaway electrons
National Category
Meteorology and Atmospheric Sciences Engineering and Technology
Research subject
Engineering Science with specialization in Atmospheric Discharges
Identifiers
urn:nbn:se:uu:diva-268859 (URN)10.1016/j.jastp.2016.07.012 (DOI)000395952000019 ()
Funder
Swedish Research Council, 621-2012-3300
Available from: 2015-12-10 Created: 2015-12-10 Last updated: 2018-01-08Bibliographically approved
Gunasekara, T. A., Fernando, M., Sonnadara, U. & Cooray, V. (2016). Characteristics of Narrow Bipolar Pulses observed from lightning in Sri Lanka. Journal of Atmospheric and Solar-Terrestrial Physics, 138, 66-73.
Open this publication in new window or tab >>Characteristics of Narrow Bipolar Pulses observed from lightning in Sri Lanka
2016 (English)In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 138, 66-73 p.Article in journal (Refereed) Published
Abstract [en]

A detailed study on electric field characteristics of Narrow Bipolar Pulses (NBP) observed in Sri Lanka is presented here. NBP5 analyzed in this work were recorded at a coastal location in the Southern part of Sri Lanka (Matara: 5.95 degrees N, 8.53 degrees E), from five highly active consecutive thunderstorm days during the month of May in 2013. The waveforms were recorded with a 10 ns resolution within a 100 ms time window. Both positive and negative NBP5 were observed in this study with the negative type being the most frequent. Parameters presented in this study were the rise time (Tr), zero crossing time (Tz), the duration of slow front (Ts), the full width of half maximum (FWHM), the pulse duration and the ratio of amplitude of overshoot to the corresponding peak amplitude (Os/Pa). The corresponding average values of negative NBP5 for these parameters were found to be 0.58 mu s, 3.01 mu s, 0.20 mu s, 138 mu s, 19.21 mu s and 0.19 respectively. Similarly, for positive events corresponding values were 1.38 mu s, 4.66 mu s, 0.48 mu s, 1.93 mu s, 16.42 mu s and 0.37 respectively. The above values conforms to a much narrower bipolar events when compared to previously reported values which is considered to be caused by the propagation effects of signals captured by the apparatus.

Keyword
Lightning, Electric field signatures, Narrow Bipolar Pulses, Sri Lanka
National Category
Meteorology and Atmospheric Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-281962 (URN)10.1016/j.jastp.2015.12.010 (DOI)000370769900007 ()
Available from: 2016-04-01 Created: 2016-04-01 Last updated: 2017-11-30Bibliographically approved
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