| 1. |
- Gunasekara, T. A. L. N., et al.
(author)
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Electric field signatures of narrow negative bipolar pulse activities from lightning observed in Sri Lanka
- 2014
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In: 2014 INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP). - : IEEE conference proceedings. - 9781479935444 ; , s. 624-628
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Conference paper (peer-reviewed)abstract
- Isolated Narrow Bipolar Pulses (NBP) have been observed in the past in sub tropical and tropical regions. This study presents detail electric field characteristics of NBP pulses observed in Sri Lanka in the tropic. NBP analyzed in this work were recorded at Matara (5.95 degrees N, 8.53 degrees E), southern coast of Sri Lanka from four highly active thunderstorm days in May 2013. The waveforms were recorded with a 10 ns resolution within a 100 ms time window. In contrary to previous observations at the same geographical region, both positive and negative NBP pulses were observed in this study. Parameters related to Narrow Negative Bipolar Pulses (NNBP) are presented in this study since majority of the observations were in that category. The parameters measured for NNBP's were rise time (Tr), zero crossing time (Tz), the duration of slow front (Ts), the full width at half maximum (FWHM) and the ratio of amplitude of overshoot to the corresponding peak amplitude (Os/Pa). The corresponding average values for these parameters were found to be 0.49 mu s, 2.83 mu s, 0.18 mu s, 1.18 mu s and 0.17 respectively. The above values conforms to a much narrower bipolar pulses when compared to values reported in earlier studies.
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| 2. |
- Gunasekara, T. A. L. N., et al.
(author)
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Characteristics of Narrow Bipolar Pulses observed from lightning in Sri Lanka
- 2016
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In: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826 .- 1879-1824. ; 138, s. 66-73
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Journal article (peer-reviewed)abstract
- A detailed study on electric field characteristics of Narrow Bipolar Pulses (NBP) observed in Sri Lanka is presented here. NBP5 analyzed in this work were recorded at a coastal location in the Southern part of Sri Lanka (Matara: 5.95 degrees N, 8.53 degrees E), from five highly active consecutive thunderstorm days during the month of May in 2013. The waveforms were recorded with a 10 ns resolution within a 100 ms time window. Both positive and negative NBP5 were observed in this study with the negative type being the most frequent. Parameters presented in this study were the rise time (Tr), zero crossing time (Tz), the duration of slow front (Ts), the full width of half maximum (FWHM), the pulse duration and the ratio of amplitude of overshoot to the corresponding peak amplitude (Os/Pa). The corresponding average values of negative NBP5 for these parameters were found to be 0.58 mu s, 3.01 mu s, 0.20 mu s, 138 mu s, 19.21 mu s and 0.19 respectively. Similarly, for positive events corresponding values were 1.38 mu s, 4.66 mu s, 0.48 mu s, 1.93 mu s, 16.42 mu s and 0.37 respectively. The above values conforms to a much narrower bipolar events when compared to previously reported values which is considered to be caused by the propagation effects of signals captured by the apparatus.
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| 3. |
- Gunasekara, T. A. L. N., et al.
(author)
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Horizontal electric fields of lightning return strokes and narrow bipolar pulses observed in Sri Lanka
- 2018
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In: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826 .- 1879-1824. ; 173, s. 57-65
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Journal article (peer-reviewed)abstract
- Simultaneous measurement of both vertical and horizontal electric field signatures of lightning was carried out in an elevated location in Colombo, Sri Lanka. The experimental setup used in this work was similar to an earlier study carried out by a different group in the late 1980s. To our knowledge, this is the first instance that such a study is conducted in this region. Data were acquired during the active months (April-May) of the southwest monsoon period in 2014. Lightning flashes from the most active thunderstorm was analyzed by selecting 65 Return Strokes (RS), 50 Negative Narrow Bipolar Pulses (NNBP) and 40 Positive Narrow Bipolar Pulses (PNBP). The wave shapes were initially validated against results of a previous study and subsequently via a theoretical method as well. Since the direction and the distance information was not available, rather than the amplitudes, ratios of the peak amplitudes of vertical electric field (Ev) and corresponding horizontal electric field (Eh) were compared. The average ratio for the return stroke was 0.024 +/- 0.008. The same for the NNBP was 0.041 +/- 0.004. The PNBP had a ratio of 0.031 +/- 0.006. The average 10%-90% rise times (Tr) for Ev for RS, NNBP and PNBP was 2.124 +/- 1.088 mu s, 0.734 +/- 0.077 is and 1.141 +/- 0.311 mu s respectively. The Tr values for Eh for RS, NNBP and PNBP were 1.865 +/- 1.200 mu s, 0.538 +/- 0.061 mu s and 1.086 +/- 0.423 mu s.
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| 4. |
- Gunasekara, T. A. L. N., et al.
(author)
-
Time-Frequency Analysis of Narrow Bipolar Pulses observed in Sri Lanka
- 2016
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In: 2016 33RD INTERNATIONAL CONFERENCE ON LIGHTNING PROTECTION (ICLP). - 9781509058433
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Conference paper (peer-reviewed)abstract
- Narrow Bipolar Pulses (NBP) of a single thunderstorm from a coastal location in Sri Lanka were subjected to S-transformation in order to study their time frequency information. This study is an extension to a similar study carried out by the authors where properties of NBPs were analyzed using the wavelet transformation. Keeping in line with the previous study, 18 events pertaining to equal number of positive and negative NBPs with the narrowest temporal widths were studied. The data was obtained from the southern coastal area of Sri Lanka (Matara - 5.95 degrees N, 8.53 degrees E) from a highly active thunderstorm, which occurred during the month of May in 2013. The waveforms were recorded with a 10 ns resolution within a 100 ms time window. The spanning (width) and the ratio of peak power amongst the initial and overshoot pulses were measured and compared for each polarity. The negative NBPs had an average spanning of 134 - 371 kHz. The overshoot of the same had an average range of 127 - 255 kHz. The positive NBPs had an average spanning of 103 - 245 kHz. The overshoot of the same had an average range of 102 - 195 kHz. The ratio of peak power of NBPs to overshoot had an average of 1.08 for both positive and negative pulses. The spectrogram reveals the initial and overshoots pulses to be relatively equal in power intensities.
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| 5. |
- Vayanganie, S. P. A., et al.
(author)
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Optical observations of electrical activity in cloud discharges
- 2018
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In: Journal of Atmospheric and Solar-Terrestrial Physics. - : PERGAMON-ELSEVIER SCIENCE LTD. - 1364-6826 .- 1879-1824. ; 172, s. 24-32
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Journal article (peer-reviewed)abstract
- Temporal variation of the luminosity of seven natural cloud-to-cloud lightning channels were studied, and results were presented. They were recorded by using a high-speed video camera with the speed of 5000 fps (frames per second) and the pixel resolution of 512 x 512 in three locations in Sri Lanka in the tropics. Luminosity variation of the channel with time was obtained by analyzing the image sequences. Recorded video frames together with the luminosity variation were studied to understand the cloud discharge process. Image analysis techniques also used to understand the characteristics of channels. Cloud flashes show more luminosity variability than ground flashes. Most of the time it starts with a leader which do not have stepping process. Channel width and standard deviation of intensity variation across the channel for each cloud flashes was obtained. Brightness variation across the channel shows a Gaussian distribution. The average time duration of the cloud flashes which start with non stepped leader was 180.83 ms. Identified characteristics are matched with the existing models to understand the process of cloud flashes. The fact that cloud discharges are not confined to a single process have been further confirmed from this study. The observations show that cloud flash is a basic lightning discharge which transfers charge between two charge centers without using one specific mechanism.
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