Vernon Cooray | Uppsala University (original) (raw)

Papers by Vernon Cooray

Research paper thumbnail of On the occurrence of ‘bead lightning’ phenomena in long laboratory sparks

Physics Letters A, 2016

Abstract The formation of bead lightning, where the lightning channel appears to break up into lu... more Abstract The formation of bead lightning, where the lightning channel appears to break up into luminous fragments, is still an object of speculation. Here we report similar observations in laboratory discharges. Analysis of time resolved photographs shows that the discharge channel exhibits a ‘bead pattern’ in the decaying stage of the discharge and the occurrence of loops in the channel sections where the bead pattern is observed. This result presents the first evidence that the rapid cooling of non-uniform channel sections could lead to the formation of beads. It is suggested that periodically occurring non-uniform channel sections could explain the bead pattern of lightning discharges.

Research paper thumbnail of Production of X-rays in air gaps stressed by switching impulse voltages

We present for the first time detection of X-rays from laboratory sparks created in air at atmosp... more We present for the first time detection of X-rays from laboratory sparks created in air at atmospheric pressure by applying an impulse voltage with slow rise time. It is in full analogy with the detection of X-rays from lightning stepped and

Research paper thumbnail of Direct measurement of NOx produced by lightning

Research paper thumbnail of A Universal Condition Satisfied by the Action of Electromagnetic Radiation Fields

Journal of Electromagnetic Analysis and Applications, 2017

Research paper thumbnail of Lightning parameters for engineering applications (keynote speech)

2010 Asia-Pacific International Symposium on Electromagnetic Compatibility, 2010

ABSTRACT

Research paper thumbnail of Identification of lightning vulnerability points on complex grounded structures

Journal of Electrostatics, 2007

Research paper thumbnail of An experimental quantification of the NOX production efficiency of energetic alpha particles in air

Journal of Atmospheric and Solar-Terrestrial Physics, 2006

ABSTRACT

Research paper thumbnail of On the Remarkable Features of the Lower Limits of Charge and the Radiated Energy of Antennas as Predicted by Classical Electrodynamics

Research paper thumbnail of Exact Expressions for Lightning Electromagnetic Fields: Application to the Rusck Field-to-Transmission Line Coupling Model

Atmosphere

An exact analytical expression for the electric field of the return stroke as excited by a propag... more An exact analytical expression for the electric field of the return stroke as excited by a propagating step current source is derived in this paper. This expression could be advantageously used to evaluate the disturbances caused by lightning on overhead lines. There are three equivalent procedures to evaluate the voltages induced by lightning on power lines, namely, the Agrawal–Price–Gurbaxani model, the Taylor–Satterwhite–Harrison model, and the Rachidi model. In the case of a vertical return stroke channel, the coupling model developed by Rusck becomes identical to these three coupling models. Due to its simplicity, the Rusck model is frequently used by engineers to study the effects of lightning on power distribution and transmission lines. In order to reduce the time involved in the electromagnetic field calculation, the Rusck model is incorporated with an analytical expression for the electromagnetic fields of the return stroke excited by a propagating step current pulse. Our ...

Research paper thumbnail of Effects of Propagation of Narrow Bipolar Pulses, Generated by Compact Cloud Discharges, Over Finitely Conducting Ground

Propagation effects on the Narrow Bipolar Pulses (NBPs) or the radiation fields generated by comp... more 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 are 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.

Research paper thumbnail of A theoretical study on the consequence of a direct lightning strike to electrified railway system in Sweden

Electric Power Systems Research, 2005

Direct lightning strike to a single-track electrified railway system in Sweden is modeled in this... more Direct lightning strike to a single-track electrified railway system in Sweden is modeled in this paper. Using this model, the induced voltages in each of the nine conductors at heights varying from 0.5m (tracks) to 10m above the ground are estimated. The effect of the finitely conducting ground is included using a time domain expression for the transient ground impedance

Research paper thumbnail of The Performance Evaluation of Capacitive Antenna with Various Structures and Permittivity Values

2018 International Conference on Electrical Engineering and Computer Science (ICECOS)

Research paper thumbnail of The Energy, Momentum, and Peak Power Radiated by Negative Lightning Return Strokes

Research paper thumbnail of Wavelet Analysis of the Onset of VHF and Microwave Radiation Emitted by Lightning

2018 International Conference on Electrical Engineering and Computer Science (ICECOS)

Research paper thumbnail of Time-frequency analysis of narrow bipolar pulses observed in Sri Lanka

2016 33rd International Conference on Lightning Protection (ICLP)

Research paper thumbnail of Modified Transmission Line Model with a Current Attenuation Function Derived from the Lightning Radiation Field—MTLD Model

Atmosphere

In return strokes, the parameters that can be measured are the channel base current and the retur... more In return strokes, the parameters that can be measured are the channel base current and the return stroke speed. For this reason, many return stroke models have been developed with these two parameters, among others, as inputs. Here, we concentrate on the current propagation type engineering return stroke models where the return stroke is represented by a current pulse propagating upwards along the leader channel. In the current propagation type return stroke models, in addition to the channel base current and the return stroke speed, the way in which the return stroke current attenuates along the return stroke channel is specified as an input parameter. The goal of this paper is to show that, within the confines of current propagation type models, once the channel base current and the return stroke speed are known, the measured radiation field can be used to evaluate how the return stroke current attenuates along the channel. After giving the mathematics necessary for this inverse ...

Research paper thumbnail of Some characteristics of subsequent return strokes in positive ground flash in Sweden

This paper presents the characteristics of the first and subsequent strokes observed in positive ... more This paper presents the characteristics of the first and subsequent strokes observed in positive ground flashes during 2014 summer thunderstorms in Uppsala, Sweden. We obtained the average number of strokes in the positive ground flashes and the relative amplitude of the subsequent stroke peak to the first stroke peak. We also determined the characteristics of the first and subsequent strokes, and compared the values between them. In our analysis, only 12% of the cases were multiple-stroke flashes while majority (88%) were single-stroke flashes. On average, the number of strokes per flash was 1.20 and the highest number of strokes per flash recorded was 4. The relative peak amplitude of the subsequent stroke to the first stroke peak was 0.83 with values ranging between 0.09 and 2.33. As for the stroke characteristics, we found that the average values for all parameters for the subsequent stroke were smaller than that of the first stroke. The average values for the slow front duratio...

Research paper thumbnail of VHF Emissions Prior to the Onset of Initial Electric Field Changes of Intracloud Flashes

2018 International Conference on Electrical Engineering and Computer Science (ICECOS)

Research paper thumbnail of Polarity Asymmetry in Lightning Return Stroke Speed Caused by the Momentum Associated with Radiation

Atmosphere

In positive lightning return strokes, the net momentum transported by the radiation field has the... more In positive lightning return strokes, the net momentum transported by the radiation field has the same direction as the momentum associated with electrons, whereas the momentum associated with electrons is in opposite direction to the momentum of radiation in negative return strokes. It is shown here that this polarity asymmetry could limit the maximum speed of positive return strokes with respect to the negative return strokes.

Research paper thumbnail of Nterference from Cloud-To-Ground and Cloud Flashes in Wireless Ommunication System Ohd

In this study, cloud-to-ground (CG) flash and intra-cloud (IC) flash events that interfere with t... more In this study, cloud-to-ground (CG) flash and intra-cloud (IC) flash events that interfere with the transmission of bits in wireless communication system operating at 2.4 GHz were analyzed. Bit error rate (BER) and consecutive lost datagram (CLD) measurement methods were used to evaluate BER and burst error from 3 tropical thunderstorms on November 27, 28, and 29 during 2012 northeastern monsoon in Malaysia. A total of 850 waveforms from the electric field change recording system were recorded and examined. Out of these, 94 waveforms of very fine structure were selected which matched perfectly with the timing information of the recorded BER. We found that both CG and IC flashes interfered significantly with the transmission of bits in wireless communication system. The severity of the interference depends mainly on two factors namely the number of pulses and the amplitude intensity of the flash. The interference level becomes worst when the number of pulses in a flash increases and ...

Research paper thumbnail of On the occurrence of ‘bead lightning’ phenomena in long laboratory sparks

Physics Letters A, 2016

Abstract The formation of bead lightning, where the lightning channel appears to break up into lu... more Abstract The formation of bead lightning, where the lightning channel appears to break up into luminous fragments, is still an object of speculation. Here we report similar observations in laboratory discharges. Analysis of time resolved photographs shows that the discharge channel exhibits a ‘bead pattern’ in the decaying stage of the discharge and the occurrence of loops in the channel sections where the bead pattern is observed. This result presents the first evidence that the rapid cooling of non-uniform channel sections could lead to the formation of beads. It is suggested that periodically occurring non-uniform channel sections could explain the bead pattern of lightning discharges.

Research paper thumbnail of Production of X-rays in air gaps stressed by switching impulse voltages

We present for the first time detection of X-rays from laboratory sparks created in air at atmosp... more We present for the first time detection of X-rays from laboratory sparks created in air at atmospheric pressure by applying an impulse voltage with slow rise time. It is in full analogy with the detection of X-rays from lightning stepped and

Research paper thumbnail of Direct measurement of NOx produced by lightning

Research paper thumbnail of A Universal Condition Satisfied by the Action of Electromagnetic Radiation Fields

Journal of Electromagnetic Analysis and Applications, 2017

Research paper thumbnail of Lightning parameters for engineering applications (keynote speech)

2010 Asia-Pacific International Symposium on Electromagnetic Compatibility, 2010

ABSTRACT

Research paper thumbnail of Identification of lightning vulnerability points on complex grounded structures

Journal of Electrostatics, 2007

Research paper thumbnail of An experimental quantification of the NOX production efficiency of energetic alpha particles in air

Journal of Atmospheric and Solar-Terrestrial Physics, 2006

ABSTRACT

Research paper thumbnail of On the Remarkable Features of the Lower Limits of Charge and the Radiated Energy of Antennas as Predicted by Classical Electrodynamics

Research paper thumbnail of Exact Expressions for Lightning Electromagnetic Fields: Application to the Rusck Field-to-Transmission Line Coupling Model

Atmosphere

An exact analytical expression for the electric field of the return stroke as excited by a propag... more An exact analytical expression for the electric field of the return stroke as excited by a propagating step current source is derived in this paper. This expression could be advantageously used to evaluate the disturbances caused by lightning on overhead lines. There are three equivalent procedures to evaluate the voltages induced by lightning on power lines, namely, the Agrawal–Price–Gurbaxani model, the Taylor–Satterwhite–Harrison model, and the Rachidi model. In the case of a vertical return stroke channel, the coupling model developed by Rusck becomes identical to these three coupling models. Due to its simplicity, the Rusck model is frequently used by engineers to study the effects of lightning on power distribution and transmission lines. In order to reduce the time involved in the electromagnetic field calculation, the Rusck model is incorporated with an analytical expression for the electromagnetic fields of the return stroke excited by a propagating step current pulse. Our ...

Research paper thumbnail of Effects of Propagation of Narrow Bipolar Pulses, Generated by Compact Cloud Discharges, Over Finitely Conducting Ground

Propagation effects on the Narrow Bipolar Pulses (NBPs) or the radiation fields generated by comp... more 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 are 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.

Research paper thumbnail of A theoretical study on the consequence of a direct lightning strike to electrified railway system in Sweden

Electric Power Systems Research, 2005

Direct lightning strike to a single-track electrified railway system in Sweden is modeled in this... more Direct lightning strike to a single-track electrified railway system in Sweden is modeled in this paper. Using this model, the induced voltages in each of the nine conductors at heights varying from 0.5m (tracks) to 10m above the ground are estimated. The effect of the finitely conducting ground is included using a time domain expression for the transient ground impedance

Research paper thumbnail of The Performance Evaluation of Capacitive Antenna with Various Structures and Permittivity Values

2018 International Conference on Electrical Engineering and Computer Science (ICECOS)

Research paper thumbnail of The Energy, Momentum, and Peak Power Radiated by Negative Lightning Return Strokes

Research paper thumbnail of Wavelet Analysis of the Onset of VHF and Microwave Radiation Emitted by Lightning

2018 International Conference on Electrical Engineering and Computer Science (ICECOS)

Research paper thumbnail of Time-frequency analysis of narrow bipolar pulses observed in Sri Lanka

2016 33rd International Conference on Lightning Protection (ICLP)

Research paper thumbnail of Modified Transmission Line Model with a Current Attenuation Function Derived from the Lightning Radiation Field—MTLD Model

Atmosphere

In return strokes, the parameters that can be measured are the channel base current and the retur... more In return strokes, the parameters that can be measured are the channel base current and the return stroke speed. For this reason, many return stroke models have been developed with these two parameters, among others, as inputs. Here, we concentrate on the current propagation type engineering return stroke models where the return stroke is represented by a current pulse propagating upwards along the leader channel. In the current propagation type return stroke models, in addition to the channel base current and the return stroke speed, the way in which the return stroke current attenuates along the return stroke channel is specified as an input parameter. The goal of this paper is to show that, within the confines of current propagation type models, once the channel base current and the return stroke speed are known, the measured radiation field can be used to evaluate how the return stroke current attenuates along the channel. After giving the mathematics necessary for this inverse ...

Research paper thumbnail of Some characteristics of subsequent return strokes in positive ground flash in Sweden

This paper presents the characteristics of the first and subsequent strokes observed in positive ... more This paper presents the characteristics of the first and subsequent strokes observed in positive ground flashes during 2014 summer thunderstorms in Uppsala, Sweden. We obtained the average number of strokes in the positive ground flashes and the relative amplitude of the subsequent stroke peak to the first stroke peak. We also determined the characteristics of the first and subsequent strokes, and compared the values between them. In our analysis, only 12% of the cases were multiple-stroke flashes while majority (88%) were single-stroke flashes. On average, the number of strokes per flash was 1.20 and the highest number of strokes per flash recorded was 4. The relative peak amplitude of the subsequent stroke to the first stroke peak was 0.83 with values ranging between 0.09 and 2.33. As for the stroke characteristics, we found that the average values for all parameters for the subsequent stroke were smaller than that of the first stroke. The average values for the slow front duratio...

Research paper thumbnail of VHF Emissions Prior to the Onset of Initial Electric Field Changes of Intracloud Flashes

2018 International Conference on Electrical Engineering and Computer Science (ICECOS)

Research paper thumbnail of Polarity Asymmetry in Lightning Return Stroke Speed Caused by the Momentum Associated with Radiation

Atmosphere

In positive lightning return strokes, the net momentum transported by the radiation field has the... more In positive lightning return strokes, the net momentum transported by the radiation field has the same direction as the momentum associated with electrons, whereas the momentum associated with electrons is in opposite direction to the momentum of radiation in negative return strokes. It is shown here that this polarity asymmetry could limit the maximum speed of positive return strokes with respect to the negative return strokes.

Research paper thumbnail of Nterference from Cloud-To-Ground and Cloud Flashes in Wireless Ommunication System Ohd

In this study, cloud-to-ground (CG) flash and intra-cloud (IC) flash events that interfere with t... more In this study, cloud-to-ground (CG) flash and intra-cloud (IC) flash events that interfere with the transmission of bits in wireless communication system operating at 2.4 GHz were analyzed. Bit error rate (BER) and consecutive lost datagram (CLD) measurement methods were used to evaluate BER and burst error from 3 tropical thunderstorms on November 27, 28, and 29 during 2012 northeastern monsoon in Malaysia. A total of 850 waveforms from the electric field change recording system were recorded and examined. Out of these, 94 waveforms of very fine structure were selected which matched perfectly with the timing information of the recorded BER. We found that both CG and IC flashes interfered significantly with the transmission of bits in wireless communication system. The severity of the interference depends mainly on two factors namely the number of pulses and the amplitude intensity of the flash. The interference level becomes worst when the number of pulses in a flash increases and ...