Time-Frequency Analysis of vertical and horizontal electric field changes of lightning negative return strokes observed in Sri Lanka. (November 2018)

• Record Type: Journal Article
• Authors: Gunasekara, T.A.L.N.; Jayalal, S.N.; Fernando, M.; Sonnadara, U.; Cooray, V.
• Is Part Of: Journal of atmospheric and solar-terrestrial physics. Volume 179(2018)
• Page Start: 34
• Page End: 39
• Publication Date: 2018-11
• Subjects: Geophysics -- Periodicals; Atmospheric physics -- Periodicals; Géophysique -- Périodiques; Météorologie physique -- Périodiques; Electronic journals; 551.51
• DOI: 10.1016/j.jastp.2018.06.015
• Languages: English
• ISSNs: 1364-6826

Abstract

Abstract: 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. Highlights: 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.