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 μs, 0.734 ± 0.077 μs and 1.141 ± 0.311 μs respectively. The Tr values for Eh for RS, NNBP and PNBP were 1.865 ± 1.200 μs, 0.538 ± 0.061 μs and 1.086 ± 0.423 μs.
•Vertical and horizontal electric fields of lightning return strokes and narrow bipolar pulses were simultaneously measured.•It's the sixth data set of horizontal field recordings of lightning and the very first time for Narrow Bipolar Pulses.•Data were validated visually and theoretically by using a mathematical formula.•Peak amplitude ratios of the vertical and horizontal E-fields of NBPs showed a higher ratio compared to the RSs.•Average rise times of the vertical E-fields were larger than horizontal E-fields for both RSs and NBPs.
The accuracy of reconstructing missing daily temperature extremes in the Jaffna climatological station, situated in the northern part of the dry zone of Sri Lanka, is presented. The adopted method ...utilizes standard departures of daily maximum and minimum temperature values at four neighbouring stations, Mannar, Anuradhapura, Puttalam and Trincomalee to estimate the standard departures of daily maximum and minimum temperatures at the target station, Jaffna. The daily maximum and minimum temperatures from 1966 to 1980 (15 years) were used to test the validity of the method. The accuracy of the estimation is higher for daily maximum temperature compared to daily minimum temperature. About 95% of the estimated daily maximum temperatures are within ±1.5 °C of the observed values. For daily minimum temperature, the percentage is about 92. By calculating the standard deviation of the difference in estimated and observed values, we have shown that the error in estimating the daily maximum and minimum temperatures is ±0.7 and ±0.9 °C, respectively. To obtain the best accuracy when estimating the missing daily temperature extremes, it is important to include Mannar which is the nearest station to the target station, Jaffna. We conclude from the analysis that the method can be applied successfully to reconstruct the missing daily temperature extremes in Jaffna where no data is available due to frequent disruptions caused by civil unrests and hostilities in the region during the period, 1984 to 2000.
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 × 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.
•For the first time, detailed comparison was done between the theoretically existing model and the optical observations of cloud flashes in the tropics (Sri Lanka).•Most of the time what we observe as cloud flashes can be actually the leader activities occurring in the lower part of the full cloud discharge event.•Statistics of cloud flashes were reported.•A possible mechanism for the cloud flashes is proposed.
Simultaneously captured vertical and horizontal (total) electric field signatures of lightning negative Return Strokes (RS) were analyzed to obtain Time-Frequency (TF) variation using Stockwell ...Transformation (ST). In the study, ST was utilized since it is known to possess comparatively better time resolution at high frequency regions compared to other available TF methods. The data were obtained during the monsoon season of April–May 2014. The vertical and horizontal component of fifty negative RSs was utilized in the study. The resultant ST spectrum was analyzed and the regions of interest were demarcated based on the color which represented their relative power output intensities for different frequency components of the signal. The spread area was identified as the region of frequencies which consisted of power intensity equal or above 90th percentile when compared to the maximum possible value. The spectral area was identified as the area of frequencies in the borderline to the natural background noise. The spread region for the vertical E field had a range between 10 kHz and 650 kHz. Its average values were in between 126 kHz and 331 kHz. The spectral region of the vertical electric field change spanned from 1 kHz to 1020 kHz. Its average distribution was 44 kHz–660 kHz. Horizontal electric fields had a range of 20 kHz–1940 kHz in the spectral region. The same for the spread region was 80 kHz–910 kHz. The averages of the horizontal E field's spectral region were 46–1112 kHz and its spread region varied between 227 and 599 kHz. The results display a higher frequency range for all aspects of the horizontal E field changes which implies that its influence on the high frequency radiation is much higher than its vertical counterpart.
•Simultaneously measured vertical & horizontal electric fields of lightning negative return strokes were stockwell transformed.•This is the first known instance that such an analysis is done on the total electric fields of RSs.•Data were validated visually and theoretically by using an approach used by the authors in a previous different study.•All horizontal components showed a higher frequency range than its vertical counterpart.•It implies that the horizontal component has a greater influence on radiation emissions of lightning.
A basic broadband digital interferometer was developed, which is capable of locating Very High Frequency (VHF) radiation sources in two spatial dimensions and time. Three antennas sensed the time ...series of broadband electromagnetic (EM) signals and digitized with 4 ns sampling interval for a duration of several milliseconds. A technique based on cross-correlations has been implemented for mapping lightning source locations. A map of the first return stroke (RS) and the preceding stepped leader was mapped successfully, using the system with a time resolution of few milliseconds. The result was compared with the visible events of the ground flash to validate the system.
Directed flow of antiprotons is studied in Au+Au collisions at a beam momentum of 11.5A GeV/c. It is shown that antiproton directed flow is anti-correlated to proton flow. The measured transverse ...momentum dependence of the antiproton flow is compared with predictions of the RQMD event generator.
We present measurements of pion transverse momentum (
p
t) spectra in central Si-nucleus collisions in the rapidity range 2.0 <
y < 5.0 for
p
t down to and including
p
t = 0. The data exhibit an ...enhanced pion yield at low
p
t compared to what is expected for a purely thermal spectral shape. This enhancement is used to determine the Δ resonance abundance at freeze-out. The results are consistent with a direct measurement of the Δ resonance yield by reconstruction of proton-pion pairs and imply a temperature of the system at freeze-out close to 140 MeV.
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