| 1. |
- Baharudin, Zikri A., et al.
(author)
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Comparative study on preliminary breakdown pulse trains observed in Johor, Malaysia and Florida, USA
- 2012
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In: Atmospheric research. - : Elsevier BV. - 0169-8095 .- 1873-2895. ; 117, s. 111-121
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Journal article (peer-reviewed)abstract
- In this paper, the preliminary breakdown (PB) pulse train preceding the negative first return stroke (RS) is recorded using a broad band antenna system. These analyses were carried out in Johor Bahru, Malaysia and Florida, United States. This is a novel initiative at examining and identifying the characteristics of the PB pulse trains in the negative cloud-to-ground flashes observed in Malaysia. The arithmetic mean of the total pulse train duration is 12.3 ms and the weighted arithmetic mean of the pulse durations and interpulse intervals are 11 mu s and 152 mu s, respectively. The arithmetic mean ratio between the maximum peak amplitude of the PB pulse and the peak RS electric field was 27.8%, and the corresponding value in Florida was 29.4%. The arithmetic mean of the time duration between the most active part of the pulse train, and the RS was 57.6 ms in Malaysia and 22 ms in Florida. A qualitative comparison of our results with those obtained earlier in Sri Lanka. Sweden and Finland supports the hypothesis that the PBP/RS ratio is higher in the northern regions compared to the tropical regions. (C) 2012 Elsevier B.V. All rights reserved.
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| 2. |
- Becerra, Marley
(author)
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Corona discharges and their effect on lightning attachment revisited : Upward leader initiation and downward leader interception
- 2014
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In: Atmospheric research. - : Elsevier BV. - 0169-8095 .- 1873-2895. ; 149, s. 316-323
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Journal article (peer-reviewed)abstract
- Previous studies have suggested the possibility of using glow corona discharges to control the frequency of lightning flashes to grounded objects. In order to revisit the theoretical basis of this proposal, the self-consistent leader inception and propagation model - SLIM - is used together with a two-dimensional glow corona drift model. The analysis is performed to quantify the effect of glow corona generated at the tip of ground-based objects on the initiation and propagation of upward positive connecting leaders under the influence of downward lightning leaders. It is found that the presence of glow corona does not influence the performance of Franklin lightning rods shorter than 15 m, while it slightly reduces the lateral distance of rods up to 60 m tall by a maximum of 10%. Furthermore, the results indicate that it is not possible to suppress the initiation of upward connecting leaders by means of glow corona. It is found instead that unconventional lightning protection systems based on the generation of glow corona attract downward lightning flashes in a similar way as a standard lightning rod with the same height.
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| 3. |
- Cooray, Vernon, et al.
(author)
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Attractive radii of vertical and horizontal conductors evaluated using a self consistent leader inception and propagation model—SLIM
- 2012
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In: Atmospheric research. - : Elsevier BV. - 0169-8095 .- 1873-2895. ; 117:SI, s. 64-70
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Journal article (peer-reviewed)abstract
- 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.
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| 4. |
- Cooray, Vernon, et al.
(author)
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Electromagnetic fields of a relativistic electron avalanche with special attention to the origin of lightning signatures known as narrow bipolar pulses
- 2014
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In: Atmospheric research. - : Elsevier BV. - 0169-8095 .- 1873-2895. ; 149, s. 346-358
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Journal article (peer-reviewed)abstract
- 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.
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| 5. |
- Cooray, Vernon, et al.
(author)
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Electromagnetic radiation field of an electron avalanche
- 2012
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In: Atmospheric research. - : Elsevier BV. - 0169-8095 .- 1873-2895. ; 117:SI, s. 18-27
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Journal article (peer-reviewed)abstract
- 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.
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| 6. |
- Cooray, Vernon, et al.
(author)
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Guest Editorial
- 2012
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In: Atmospheric research. - : Elsevier BV. - 0169-8095 .- 1873-2895. ; 117, s. 1-1
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Journal article (peer-reviewed)
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| 7. |
- Cooray, Vernon, et al.
(author)
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On the peak amplitude of lightning return stroke currents striking the sea
- 2014
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In: Atmospheric research. - : Elsevier BV. - 0169-8095 .- 1873-2895. ; 149, s. 372-376
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Journal article (peer-reviewed)abstract
- Data gathered from the US National Lightning Detection Network (TM) (NLDN) show that the peak currents of lightning flashes striking the sea are significantly higher than those of lightning flashes striking the land. We suggest that the unfavorable conditions for the formation of positive charge pockets in maritime clouds lead to lightning initiation at higher cloud potentials compared to their land counterparts, resulting in larger peak currents in negative lightning flashes striking the sea. As the positive charge pocket does not promote positive ground strokes, no such discontinuity should be expected in positive first return strokes to ground between land and sea.
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| 8. |
- Cooray, Vernon, et al.
(author)
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On the upper and lower limits of peak current of first return strokes in negative lightning flashes
- 2012
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In: Atmospheric research. - : Elsevier BV. - 0169-8095 .- 1873-2895. ; 117:SI, s. 12-17
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Journal article (peer-reviewed)abstract
- It is shown that the peak current of a return stroke is determined by the background electric field that exists between the cloud and the ground. Assuming 150 kV/m as the largest background electric field that can exist below thunderclouds, it is estimated that the largest negative first return stroke peak current that can exist in nature is about 300 kA in temperate regions and about 450 kA–500 kA in the tropics. Since corona discharges from trees, bushes and other protrusions and upward initiated discharges from tall structures limit the maximum electric field that can exist below thunderclouds over land, there is a high probability for these strong discharges to take place over the oceans. In the study it is also estimated that the smallest value of the return stroke current that can exist in nature lies in the range of 3.0 kA to 1.5 kA with the most probable value located in the vicinity of 2 kA.
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| 9. |
- Cooray, Vernon
(author)
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Power and energy dissipation in negative lightning return strokes
- 2014
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In: Atmospheric research. - : Elsevier BV. - 0169-8095 .- 1873-2895. ; 149, s. 359-371
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Journal article (peer-reviewed)abstract
- 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.
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| 10. |
- Esa, Mona Riza Mohd, et al.
(author)
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Wavelet analysis of the first electric field pulse of lightning flashes in Sweden
- 2014
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In: Atmospheric research. - : Elsevier BV. - 0169-8095 .- 1873-2895. ; 138, s. 253-267
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Journal article (peer-reviewed)abstract
- In this paper, we investigate the wavelet characteristics of the first electric field pulse of four different flash types namely negative cloud-to-ground flash (-CG), positive cloud-to-ground flash (+CG), cloud flash (IC) and isolated breakdown flash (IB). A total of 110 fine waveforms out of 885 were selected which have been recorded during summer between May and August 2010 in Uppsala, Sweden. The measurement was done by using an electric field broadband antenna system with the time resolution of 20 Megasample per second. Evidence from our wavelet analysis suggests that the ionization process during the initial leader development (coincide with the detection of the first electric field pulse) of at least three flashes (-CG, IC, and IB) in Sweden was dictated directly by the existence and magnitude of localized free ions region and lower positive charge center (p region). In general, we found that both single peak and multiple peaks pulses of the negative CG and IC flashes radiated energy at higher frequencies and gain larger bandwidth when compared to positive CG and IB flashes. We suggest that the initial leader development of both IC and negative CG flashes underwent very rapid and much more extensive ionization process when compared to the positive CG and IB flashes. In specific comparison between negative CG and IC flashes, both temporal and wavelet analyses suggest that the first electric field pulses of IC flash radiated energy at higher frequency in both single spread categories and radiated energy at lower frequency in both multiple spread categories when compared to the negative CG flash. This finding may explain the observation of much slower and less bright type alpha leader (ionization process not so extensive) compared to much faster and very bright type beta leader (ionization process very rapid and more extensive). As for positive CG and IB flashes, the single peak pulses of positive CG radiated energy at much higher frequency while the multiple peaks pulses radiated energy at much lower frequency than IB flash. We suggest that the initiation mechanism of positive CG was dictated directly by the background electric field between the main positive charge center and the ground, which is distinct from the initiation mechanism of IB flash. The presence of small magnitude of localized free ions region facilitated the rapidity of the ionization process in the initial leader development of IB flash.
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