Change search
Refine search result
1234567 101 - 150 of 332
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 101.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    On the upper limit of peak current in return strokes of lightning flashes2009Conference paper (Refereed)
  • 102.
    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.
    On the validity of several approximate theories used in quantifying the propagation effects on lightning generated electromagnetic fields2005In: VIII International Symposium on LIghtning Protection, SIPDA, Sao Paulo, Brazil, November 21-25, 2005Conference paper (Refereed)
  • 103.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    On the various approximations to calculate lightning return stroke-generated electric and magnetic fields over finitely conducting ground2012In: Lightning Electromagnetics / [ed] Vernon Cooray, IET , 2012, p. 427-484Chapter in book (Refereed)
    Abstract [en]

    The exact solution to the electromagnetic fields generated by electric dipoles located above a finitely conducting ground plane was obtained by Sommerfeld. He presented his results in the form of a set of integrals. Since the numerical solutions of these integrals are time-consuming, attempts have been made to find approximate solutions to these integrals. In this chapter, various approximate solutions and procedures that have been used to calculate electromagnetic fields of return strokes over finitely conducting ground will be presented together with their limits of validity.

  • 104.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Origin of the Fine Scale Tortuosity in Sparks and Lightning Channels2018In: Atmosphere, ISSN 2073-4433, E-ISSN 2073-4433, Vol. 9, no 6, article id 205Article in journal (Refereed)
    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.

  • 105.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Power and energy dissipation in negative lightning return strokes2014In: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895, Vol. 149, p. 359-371Article in journal (Refereed)
    Abstract [en]

    In this paper the temporal variation of the electric field along the negative return stroke channel is calculated and this information in turn is used to evaluate the power and energy dissipation in negative return strokes. Moreover, by plugging in the results obtained here with the spark equation of Braginski, the temporal and spatial variations of the return stroke speed, the radius and the resistance of the return stroke channel were investigated. The results of the study showed that for a typical subsequent return stroke current pulse having a peak current of 12 kA in the return stroke channel: (a) The peak power dissipation is about 4 x 10(9) W/m; (ii) the energy dissipation over the first 70 mu s or so is about (2-3) x 10(3) J/m; (iii) the maximum channel radius is about 1 cm; and (iv) the resistance of the channel is about 0.5 Omega/m. The study also revealed that the speed of the return stroke is governed not only by the peak current, but also by the risetime of the current. The study shows that the speed of the return stroke increases with increasing peak current but it decreases with increasing current risetime. The results obtained using available experimental data on first return strokes indicate that the risetime of the return stroke current increases with increasing peak current. It is shown that this tendency for the first retum stroke current risetime to increase with return stroke peak current could completely mask the relationship between the first return stroke speed and return stroke peak current. It is suggested that the apparent absence of such a relationship in experimental data is caused by these variations.  

  • 106.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Propagation effects due to finitely conducting ground on lightning-generated magnetic fields evaluated using sommerfeld's integrals2009In: IEEE transactions on electromagnetic compatibility (Print), ISSN 0018-9375, E-ISSN 1558-187X, Vol. 51, no 3, p. 526-531Article in journal (Refereed)
    Abstract [en]

    The effects of finitely conducting ground on the signature of lightning-generated magnetic fields at ground level were evaluated by numerical solution of Sommerfeld's integrals. Results are presented for distances between 10 m to 1 km from the lightning channel and for ground conductivities in the range of 0.01 and 0.0001 S/m. The results obtained from the exact theory are compared with the predictions of two frequently used analytical approximations to Sommerfeld's equations. Based on that comparison, the limits of validity of these approximate theories are obtained.

  • 107.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Propagation effects on radiation field pulses generated by cloud lightning flashes2007In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 69, no 12, p. 1397-1406Article in journal (Refereed)
    Abstract [en]

    As the electromagnetic fields propagate over finitely conducting ground, selective attenuation of the high frequencies takes place. As a result. the signatures of broad-band electromagnetic radiation fields generated by lightning flashes change as they; propagate over such ground. In addition to being a function of the electrical parameters of the ground over which the electromagnetic fields propagate, these propagation effects depend on the height of their source above ground level. This makes the propagation effects on radiation fields from cloud flashes differ from those on the radiation fields generated by return strokes in ground flashes. In this paper the propagation effects on radiation field pulses of cloud flashes are illustrated and it is shown that these effects are not as severe as those of return strokes in ground flashes.

  • 108.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Return Stroke Model Based purely on the Current Dissipation Concept2014Conference paper (Refereed)
  • 109.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Return stroke models for engineering applications2012In: Lightning Electromagnetics / [ed] Vernon Cooray, The Institution of Engineering and Technology , 2012, p. 231-261Chapter in book (Refereed)
    Abstract [en]

    In this chapter, we will describe and discuss several engineering models that can be utilized either to evaluate electromagnetic fields from lightning flashes or to study the direct effects of lightning attachment to various structures including tall towers. We will start by describing the basic concepts of engineering return stroke models. This discussion will be followed by a description of various return stroke models and the equations necessary for the evaluation of electromagnetic fields using these return stroke models.

  • 110.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Return stroke models for engineering applications2009In: Lightning Protection, London: The Institution of Engineering and Technology, London, UK , 2009Chapter in book (Other (popular science, discussion, etc.))
  • 111.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Soil ionization2009In: Lightning Protection, London: The Institution of Engineering and Technology, London, UK , 2009Chapter in book (Other (popular science, discussion, etc.))
  • 112.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    The influence of lightning conductor radii on the attachment of lightning flashes2017In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 153, no SI, p. 138-143Article in journal (Refereed)
    Abstract [en]

    The influence of the tip radius of lightning conductors on their lightning attractive distance as predicted by the self-consistent leader inception and propagation model (SLIM) is presented. The results show that in the absence of any glow corona from the tip of the conductor a smaller tip radius gives rise to a larger attractive radius than a larger radius. It is suggested that the reason for the experimental observations which show that blunt conductors are more efficient lightning receptors than sharp ones is the presence of glow corona at the tip of the sharp ones during the time of lightning strikes. Moreover, in a given background electric field, the probability of the inception of glow corona at the conductor tip increases with increasing conductor height and decreasing conductor radius. Thus, in a given electric field, as the conductor height increases its radius has to be increased to avoid the inception of glow corona at the tip. For this reason, the conductor radius that performs best as a lightning interceptor depends on the height of the conductor and the best performance shift from smaller radii to larger ones with increasing height of the conductor.

  • 113.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    The Lightning Flash2014Collection (editor) (Refereed)
  • 114.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    The Similarity of the Action of Franklin and ESE Lightning Rods under Natural Conditions2018In: Atmosphere, ISSN 2073-4433, E-ISSN 2073-4433, Vol. 9, no 6, article id 225Article in journal (Refereed)
    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.

  • 115.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Arevalo, Liliana
    A Huristic Approach to Obtain the Electric Fields Necessary for the Initiation of Upward Lightning Flashes from Towers in the Presence of Glow Corona2014Conference paper (Refereed)
  • 116.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Arevalo, Liliana
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Modeling the Stepping Process of Negative Lightning Stepped Leaders2017In: Atmosphere, ISSN 2073-4433, E-ISSN 2073-4433, Vol. 8, no 12, article id 245Article in journal (Refereed)
    Abstract [en]

    A physical model based on the mechanism observed in experimental investigations is introduced to describe the formation of negative leader steps. Starting with a small length of a space leader located at the periphery of the negative streamer system of the stepped leader, the model simulates the growth and the subsequent formation of the leader step. Based on the model, the step length, the step forming time, and the propagation speed of stepped leaders as a function of the prospective return stroke peak current are estimated. The results show that the step length and the leader speed increase with increasing prospective return stroke current. The results also show that the speed of the stepped leader increases as it approaches the ground. For prospective return stroke currents in the range of 15 kA–60 kA, the step lengths lie within the range 5 m–100 m, the step forming times lie within the range 10 μs–250 μs, and the leader speed lies within the range 105 m/s −1.5 × 106 m/s. The results obtained are in reasonable agreement with the experimental observations.

  • 117.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Arevalo, Liliana
    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.
    Dwyer, Joseph
    Rassoul, Hamid
    On the possible origin of X-rays in long laboratory sparks2009In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 71, no 17-18, p. 1890-1898Article in journal (Refereed)
  • 118.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Becerra, Marley
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Attachment of lightning flashes to grounded conductors2009In: Lightning Protection, London: The Institution of Engineering and Technology, London, UK , 2009Chapter in book (Other (popular science, discussion, etc.))
  • 119.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Becerra, Marley
    Royal Technical College, Stockholm.
    Attractive radii of vertical and horizontal conductors evaluated using a self consistent leader inception and propagation model—SLIM2012In: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895, Vol. 117, no SI, p. 64-70Article in journal (Refereed)
    Abstract [en]

    A self consistent lightning connecting leader inception and propagation model (SLIM) is utilized to study the attachment of lightning flashes to grounded structures and hence to evaluate the lightning attractive radii of vertical cylindrical structures and horizontal conductors as a function of height of the structure and peak current of the first return stroke. The attractive radius is defined as the maximum lateral distance from where the structure would be able to attract a down-coming stepped leader. The results are compared with the ones that one would obtain using Electro-Geometrical Method (EGM). The results show that for structure heights of the order of 30 m or less the attractive radii obtain from SLIM do not deviate significantly (i.e. the error is less than about 20%) from the EGM values. However, for taller objects SLIM predicts significantly larger attractive radii than EGM and the error increases with increasing height.

  • 120.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Becerra, Marley
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Attractive radius and the volume of protection of vertical and horizontal conductors evaluated using a self consistent leader inception and propagation model (SLIM)2010In: 30TH International Conference on Lightning Protection, ICLP, Cagliary, Italy, 2010Conference paper (Refereed)
  • 121.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Becerra, Marley
    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.
    On the NOx generation in corona, streamer and low pressure electrical discharges2008In: The Open Atmospheric Science Journal, ISSN 1874-2823, E-ISSN 1874-2823, Vol. 2, p. 176-180Article in journal (Refereed)
  • 122.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Becerra, Marley
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    On the NOx generation in corona, streamer and low-pressure electrical discharges2012In: Lightning Electromagnetics / [ed] Vernon Corray, IET , 2012Chapter in book (Refereed)
    Abstract [en]

    An assessment of the global distribution of nitrogen oxides (NOx) is required for a satisfactory description of tropospheric chemistry and in the evaluation of the global impact of increasing anthropogenic emissions of NOx. In the mathematical models utilized for this purpose, it is necessary to have the natural as well as man-made sources of NOx in the atmosphere as inputs. Thunderstorms are a main natural source of NOx in the atmosphere and it may be the dominant source of NOx in the troposphere in equatorial and tropical South Pacific.

  • 123.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Becerra, Marley
    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.
    On the NOx production in ‘cold’ electrical discharges2007In: International Conference on Atmospheric Electricity, ICAE, Beijing, China, 2007Conference paper (Other academic)
  • 124.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. elektricitetslära och åskforskning.
    Becerra, Marley
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. elektricitetslära och åskforskning.
    Rakov, V
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. elektricitetslära och åskforskning.
    On the Electric field at the tip of dart leaders in lightning flashes2006In: Proceedings of the 28th Internat Conference on Lightning Protection, ICLP, Kanazawa, Japan, 2006, p. 339-344Conference paper (Refereed)
  • 125.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Becerra, Marley
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rakov, Vladimir
    On the electric field at the tip of dart leaders in lightning flashes2009In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 71, no 12, p. 1397-1404Article in journal (Refereed)
    Abstract [en]

    The results obtained in this study show that as the dart leader tip passes a given point on the defunct return stroke channel the electric field increases within a fraction of a microsecond to values larger than the critical electric field necessary for the initiation of cold electron runaway in low-density air comprising the channel. These results are in support of the hypothesis that cold runaway electron breakdown may play a role in the emission of X-ray bursts by dart leaders. The calculations also show that the peak power dissipated by a typical dart leader is about 300-500 MW/m and the energy dissipated within the first 10 [mu]s or so is about 500-600 J/m. Furthermore, the minimum resistance and the maximum radius of the core of a typical dart leader are estimated to be about 3 [Omega]/m and 0.003 m, respectively.

  • 126.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, C
    Andrews, C.
    Lightning caused injuries in humans2009In: Lightning Protection, London: The Institution of Engineering and Technology, London, UK , 2009Chapter in book (Other (popular science, discussion, etc.))
  • 127.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Cooray, C.
    Karolinska institutet.
    Andrews, C.J.
    Lightning caused injuries in humans2007In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 65, no 5-6, p. 386-394Article in journal (Refereed)
    Abstract [en]

    A lightning flash may interact with humans in several ways. The possible pathways of interactions are direct strike, side flash, touch voltage, step voltage, subsequent stroke, connecting leaders and shock waves. The permanent or the temporary injuries that a victim suffers depend, among other parameters, on the type of interaction through which the body is exposed to a lightning strike and the path and the strength of the electric current passing through the body. In addition to the effects of electric current passing through the body, strong light and shock waves may also interact with the body in various ways. In this paper, the different types of injuries that may result from a lightning strike are documented and they are summarized, from engineering rather than a medical perspective

  • 128.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, G.
    On the electric and magnetic fields below a single conductor overhead power line2012In: 2012 31st International Conference on Lightning Protection, ICLP 2012, 2012, p. 6344307-Conference paper (Refereed)
    Abstract [en]

    Electromagnetic fields associated with the electric current flowing along a overhead power line with a single conductor located over perfectly conducting ground are estimated using electromagnetic fields pertinent to acceleration of electric charges. It is shown that the electric and magnetic fields that exist below a long overhead power line are nothing but the radiation fields generated by the acceleration of charge at the point of injection of current into the power line.

  • 129.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, G.
    Marshall, T.
    Dwyer, J.
    Arabshahi, S.
    Electric field of a relativistic electron avalanche2012In: 2012 31st International Conference on Lightning Protection, ICLP 2012, 2012, p. 6344240-Conference paper (Refereed)
    Abstract [en]

    In the present study, electromagnetic fields of accelerating charges were utilized to evaluate the electromagnetic fields generated by a relativistic electron avalanche. In the analysis it is assumed that all the electrons in the avalanche are moving with the same speed. In other words, the growth or the decay of the number of electrons takes place only at the head of the avalanche. It is shown that the radiation is emanating only from the head of the avalanche where electrons are being accelerated. It is also shown that an analytical expression for the radiation field of the avalanche at any distance can be written directly in terms of the e-folding length of the avalanche. This makes it possible to extract directly the spatial variation of the e-folding length of the avalanche from the measured radiation fields.

  • 130.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Gerald
    Karolinska Inst, Stockholm, Sweden.
    A Novel Interpretation of the Electromagnetic Fields of Lightning Return Strokes2019In: Atmosphere, ISSN 2073-4433, E-ISSN 2073-4433, Vol. 10, no 1, article id 22Article in journal (Refereed)
    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.

  • 131.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Gerald
    A novel procedure to calculate the electromagnetic fields of lightning return strokes2010Conference paper (Refereed)
  • 132.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Gerald
    Karolinska Univ Hosp, Dept Clin Neurosci, Stockholm, Sweden..
    Electromagnetic fields of accelerating charges: Applications in lightning protection2017In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 145, p. 234-247Article in journal (Refereed)
    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.

  • 133.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Gerald
    Karolinska Institute, Stockholm.
    Electromagnetic radiation field of an electron avalanche2012In: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895, Vol. 117, no SI, p. 18-27Article in journal (Refereed)
    Abstract [en]

    Electron avalanches are the main constituent of electrical discharges in the atmosphere. However, the electromagnetic radiation field generated by a single electron avalanche growing in different field configurations has not yet been evaluated in the literature. In this paper, the electromagnetic radiation fields created by electron avalanches were evaluated for electric fields in pointed, co-axial and spherical geometries. The results show that the radiation field has a duration of approximately 1–2 ns, with a rise time in the range of 0.25 ns. The wave-shape takes the form of an initial peak followed by an overshoot in the opposite direction. The electromagnetic spectrum generated by the avalanches has a peak around 109 Hz.

  • 134.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Gerald
    Excitation of visual sensory experiences by electromagnetic fields of lightning2012In: Lightning Electromagnetics / [ed] Vernon Cooray, IET , 2012Chapter in book (Refereed)
    Abstract [en]

    In this chapter, we will consider the possible interactions, either direct or indirect, of the lightning-generated electromagnetic fields with the brain or the visual system of humans to induce visual sensations. Some of these visual sensations are known as phosphenes in the medical literature. Since some of these visual sensations could be misinterpreted as ball lightning, this subject is of interest for lightning researchers due to the still unsolved problem of the origin of ball lightning.

  • 135.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Gerald
    Karolinska Univ Hosp, Dept Clin Neurosci, S-17176 Stockholm, Sweden..
    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 Constant2017In: Atmosphere, ISSN 2073-4433, E-ISSN 2073-4433, Vol. 8, no 3, article id 46Article in journal (Refereed)
    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.

  • 136.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Gerald
    Karolinska Univ Hosp, Dept Clin Neurosci, S-17176 Stockholm, Sweden..
    On the Momentum Transported by the Radiation Field of a Long Transient Dipole and Time Energy Uncertainty Principle2016In: Atmosphere, ISSN 2073-4433, E-ISSN 2073-4433, Vol. 7, no 11, article id 151Article in journal (Refereed)
    Abstract [en]

    The paper describes the net momentum transported by the transient electromagnetic radiation field of a long transient dipole in free space. In the dipole a current is initiated at one end and propagates towards the other end where it is absorbed. The results show that the net momentum transported by the radiation is directed along the axis of the dipole where the currents are propagating. In general, the net momentum P transported by the electromagnetic radiation of the dipole is less than the quantity U/c, where U is the total energy radiated by the dipole and c is the speed of light in free space. In the case of a Hertzian dipole, the net momentum transported by the radiation field is zero because of the spatial symmetry of the radiation field. As the effective wavelength of the current decreases with respect to the length of the dipole (or the duration of the current decreases with respect to the travel time of the current along the dipole), the net momentum transported by the radiation field becomes closer and closer to U/c, and for effective wavelengths which are much shorter than the length of the dipole, P approximate to U/c. The results show that when the condition P approximate to U/c is satisfied, the radiated fields satisfy the condition Delta t Delta U >= h/4 pi where Delta t is the duration of the radiation, Delta U is the uncertainty in the dissipated energy and h is the Plank constant.

  • 137.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Gerald
    Karolinska Univ Hosp, Dept Clin Neurosci, S-17176 Stockholm, Sweden..
    On the Remarkable Features of the Lower Limits of Charge and the Radiated Energy of Antennas as Predicted by Classical Electrodynamics2016In: Atmosphere, ISSN 2073-4433, E-ISSN 2073-4433, Vol. 7, no 5, article id 64Article in journal (Refereed)
    Abstract [en]

    Electromagnetic energy radiated by antennas working in both the frequency domain and time domain is studied as a function of the charge associated with the current in the antenna. The frequency domain results, obtained under the assumption of sinusoidal current distribution, show that, for a given charge, the energy radiated within a period of oscillation increases initially with L/lambda and then starts to oscillate around a steady value when L/lambda>1. The results show that for the energy radiated by the antenna to be equal to or larger than the energy of one photon, the oscillating charge in the antenna has to be equal to or larger than the electronic charge. That is, U >= hv or UT >= h double right arrow q >= e, where U is the energy dissipated over a period, v is the frequency of oscillation, T is the period, h is Planck's constant, q is the rms value of the oscillating charge, and e is the electronic charge. In the case of antennas working in the time domain, it is observed that U Delta t >= h/4 pi double right arrow q >= e, where U is the total energy radiated, Delta t is the time over which the energy is radiated, and q is the charge transported by the current. It is shown that one can recover the time-energy uncertainty principle of quantum mechanics from this time domain result. The results presented in this paper show that when quantum mechanical constraints are applied to the electromagnetic energy radiated by a finite antenna as estimated using the equations of classical electrodynamics, the electronic charge emerges as the smallest unit of free charge in nature.

  • 138.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Gerald
    Karolinska Univ Hosp, Dept Clin Neurosci, S-17176 Stockholm, Sweden..
    The Deep Physics Hidden within the Field Expressions of the Radiation Fields of Lightning Return Strokes2016In: Atmosphere, ISSN 2073-4433, E-ISSN 2073-4433, Vol. 7, no 2, article id UNSP 21Article in journal (Refereed)
    Abstract [en]

    Based on the electromagnetic fields generated by a current pulse propagating from one point in space to another, a scenario that is frequently used to simulate return strokes in lightning flashes, it is shown that there is a deep physical connection between the electromagnetic energy dissipated by the system, the time over which this energy is dissipated and the charge associated with the current. For a given current pulse, the product of the energy dissipated and the time over which this energy is dissipated, defined as action in this paper, depends on the length of the channel, or the path, through which the current pulse is propagating. As the length of the channel varies, the action plotted against the length of the channel exhibits a maximum value. The location of the maximum value depends on the ratio of the length of the channel to the characteristic length of the current pulse. The latter is defined as the product of the duration of the current pulse and the speed of propagation of the current pulse. The magnitude of this maximum depends on the charge associated with the current pulse. The results show that when the charge associated with the current pulse approaches the electronic charge, the value of this maximum reaches a value close to h/8 where h is the Plank constant. From this result, one can deduce that the time-energy uncertainty principle is the reason for the fact that the smallest charge that can be detected from the electromagnetic radiation is equal to the electronic charge. Since any system that generates electromagnetic radiation can be represented by a current pulse propagating from one point in space to another, the result is deemed valid for electromagnetic radiation fields in general.

  • 139.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Gerald
    The Electromagnetic Fields of an Accelerating Charge: Applications in Lightning Return-Stroke Models2010In: IEEE transactions on electromagnetic compatibility (Print), ISSN 0018-9375, E-ISSN 1558-187X, Vol. 52, no 4, p. 944-955Article in journal (Refereed)
    Abstract [en]

    In the literature, three procedures have been used to calculate the electromagnetic fields from return strokes. In the first technique, the source is described only in terms of current density and the fields are expressed entirely in terms of the return-stroke current. In the second technique, the source is expressed in terms of the current and the charge densities and the fields are given in terms of both the current and the charge density. In the third technique, the fields are expressed in terms of the apparent charge density. The fields are connected to the source terms through the vector and scalar potentials. In this paper, the standard equations for the electromagnetic fields generated by an accelerating charge are utilized to evaluate the electromagnetic fields from lightning return strokes. It is shown that the total fields evaluated at any distance using these expressions are identical to those obtained using other techniques. However, the composition of the terms that vary as 1/R, 1/R2, and 1/R3 of the total electric field is different from those of other formulations. In the case of the transmission-line model, where the return stroke is described as a current pulse propagating with uniform velocity, radiation emanates only from the bottom of the channel where current is generated. When the speed of propagation is equal to the speed of light, the total field throughout the entire space becomes radiation. The procedure is also applied here to obtain the electric fields of the traveling-current-source model. The electric fields obtained for this case, too, agree with the previous study. It is also shown how the equations can be applied rather conveniently to evaluate: 1) the electromagnetic fields generated by current pulses propagating along overhead power lines; and 2) the electromagnetic fields generated by vertical conductors and towers during lightning strikes.

  • 140.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Gerald
    Becerra, Marley
    On the streamer discharges emitted from the head of a person located in the vicinity of lightning strikes and their possible consequences2013In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 71, no 3, p. 572-576Article in journal (Refereed)
    Abstract [en]

    In this paper the currents associated with the streamer discharges generated from the head of a person located in the vicinity of a lightning strike are investigated. In the analysis the location of the person with respect to the lightning strike is selected in such a way that only a streamer burst, without the formation of a connecting leader, is emitted from the head. The current associated with these streamer bursts could exceed several hundreds of mA and may last for several hundreds of microseconds. The results of the calculation show that the passage of the streamer currents through the body of the person could create electric fields in the brain large enough to excite neurons. Depending on the strength of lightning flash and the distance to the strike point these streamer bursts can give rise to phosphenes which are a form of visual experience that occurs when the visual cortex is stimulated by electric currents.

  • 141.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Gerald
    Dept of Clinical Neuroscience, Karolinska Institutet, Stockholm.
    Dwyer, Joseph
    Florida Institute of Technology, Melbourne, FL, USA.
    On the possibility of phosphenes being generated by the energetic radiation from lightning flashes and thunderstorms2011In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 375, no 42, p. 3704-3709Article in journal (Refereed)
    Abstract [en]

    After the first report of this phenomenon by Apollo 11 astronauts, experiments conducted in space and on the ground confirmed the creation of phosphenes by the interaction of energetic radiation with the human visual system. The aim of this Letter is to show that the energetic radiation generated in the form of X-rays, gamma rays, electrons and neutrons by thunderstorms and lightning is strong enough for the creation of phosphenes in humans. It is also pointed out that some of the visual observations reported during thunderstorms might be attributable to phosphenes excited by this energetic radiation.

  • 142.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Gerald K.
    Karolinska Univ Hosp, Dept Clin Neurosci, Stockholm, Sweden..
    Cooray, Charith
    Karolinska Univ Hosp, Dept Clin Neurosci, Stockholm, Sweden..
    On the possible mechanism of keraunographic markings on lightning victims2015In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 136, no Part A, p. 119-123Article in journal (Refereed)
    Abstract [en]

    During a lightning strike to a human the high electric field that exists at the point of contact of the lightning flash can generate electrical discharges known as streamer discharges along the skin. Previous research work has shown that the electric field at the head of these streamer discharges are large enough to accelerate electrons to relativistic speeds. In this paper it is shown that the streamers propagating along the skin will bombard the skin with energetic electrons. In this paper an estimation of the energy dissipated by these energetic electrons on the skin is estimated. Since beta radiation generated by radioactive substances consists of energetic electrons the effects of the energetic electrons generated by streamer discharges would be similar to the effects caused by low level beta radiation. It is suggested that the feather like marks, called keraunographical marks, that is sometimes observed on the skin of lightning victims is a result of superficial radiation injury with following inflammation in the epidermis and superficial layers of the dermis caused by energetic electrons.

  • 143.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Gerald
    Marshall, Thomas
    Arabshahi, Shahab
    Dwyer, Joseph
    Rassoul, Hamid
    Electromagnetic fields of a relativistic electron avalanche with special attention to the origin of lightning signatures known as narrow bipolar pulses2014In: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895, Vol. 149, p. 346-358Article in journal (Refereed)
    Abstract [en]

    In the present study, electromagnetic fields of accelerating charges were utilized to evaluate the electromagnetic fields generated by a relativistic electron avalanche. In the analysis it is assumed that all the electrons in the avalanche are moving with the same speed. In other words, the growth or the decay of the number of electrons takes place only at the head of the avalanche. It is shown that the radiation is emanating only from the head of the avalanche where electrons are being accelerated. It is also shown that an analytical expression for the radiation field of the avalanche at any distance can be written directly in terms of the e-folding length of the avalanche. This model of the avalanche was utilized to test the idea whether the source of the lightning signatures known as narrow bipolar pulses could be relativistic avalanches. The idea was tested by using the simultaneously measured electric fields of narrow bipolar pulses at two distances, one measured far away from the source and the other in the near vicinity. The avalanche parameters were extracted from the distant field and they are used to evaluate the close field. The results show that the source of the NBP can be modeled either as a single or a multiple burst of relativistic avalanches with speed of avalanches in the range of 2-3 x 10(8) m/s. The multiple avalanche model agrees better with the experimental data in that it can also generate the correct signature of the time derivatives and the HF and VHF radiation bursts of NBP. 

  • 144.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cummings, Ken
    Propagation effects caused by multi-section mixed paths on electric fields of lightning return strokes2009Conference paper (Refereed)
  • 145.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. elektricitetslära och åskforskning.
    Diendorfer, G
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. elektricitetslära och åskforskning.
    Nucci, C.A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. elektricitetslära och åskforskning.
    Pavanello, D
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. elektricitetslära och åskforskning.
    Rachidi, F
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. elektricitetslära och åskforskning.
    Becerra, Marley
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. elektricitetslära och åskforskning.
    Rubinstein, M
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. elektricitetslära och åskforskning.
    Schultz, W
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. elektricitetslära och åskforskning.
    On the effect of the finite ground conductivity on electromagnetic field radiated by lightning to tall towers2006In: Proceedings of the 28th Internat Conference on Lightning Protection, ICLP, Kanazawa, Japan, 2006, p. 267-272Conference paper (Refereed)
  • 146.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Diendorfer, Gerhard
    OVE Serv GmbH, Vienna, Austria..
    Merging of current generation and current dissipation lightning return stroke models2017In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 153, no SI, p. 10-18Article in journal (Refereed)
    Abstract [en]

    Current generation and current dissipation return stroke models are engineering models based on the theory associated with the propagation of current pulses along transmission lines undergoing corona. However, neither of these models incorporates the complete theory associated with the phenomenon. One can make the physical scenario complete by combining the current generation concept with the current dissipation concept. In this paper how this can be done is demonstrated by creating a return stroke model which is a combination of these two model types. The new model encompasses the full theory associated with the pulse propagation along transmission lines under corona. The paper provides a full description of the model together with a description of the spatial and temporal variation of the return stroke current and the electric and magnetic fields generated at different distances as predicted by the model.

  • 147.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Dwyer, J.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Rassoul, H.
    On the possibility of accelerating electrons to X-ray energies in the electric fields created during the meeting of positive and negative streamer fronts in laboratory electrical discharges2007Conference paper (Other academic)
  • 148.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Dwyer, Joseph
    Rakov, V.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    On the mechanism of X-ray production by dart leaders of lightning flashes2010In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 72, p. 848-855Article in journal (Refereed)
  • 149.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Farhad, Rachidi
    Guest Editorial2012In: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895, Vol. 117, p. 1-1Article in journal (Refereed)
  • 150.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fernando, M.
    Univ Colombo, Dept Phys, Colombo 03, Sri Lanka.
    Gunasekara, L.
    Univ Colombo, Dept Phys, Colombo 03, Sri Lanka.
    Nanayakkara, S.
    Univ Colombo, Dept Phys, Colombo 03, Sri Lanka.
    Effects of Propagation of Narrow Bipolar Pulses, Generated by Compact Cloud Discharges, over Finitely Conducting Ground2018In: Atmosphere, ISSN 2073-4433, E-ISSN 2073-4433, Vol. 9, no 5, article id 193Article in journal (Refereed)
    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.

1234567 101 - 150 of 332
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf