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Earth Planets Space, Vol. 65 (No. 1), pp. 25-37, 2013
doi:10.5047/eps.2012.05.019

Lightning-associated VLF perturbations observed at low latitude: Occurrence and scattering characteristics

Sushil Kumar and Abhikesh Kumar

School of Engineering and Physics, The University of the South Pacific, Suva, Fiji

(Received November 16, 2011; Revised May 19, 2012; Accepted May 30, 2012; Online published February 19, 2013)

Abstract: The occurrence of short-timescale (∼1-100 s) perturbations (early VLF events) on four Very Low Frequency (VLF) transmitter signals (call signs: NWC, NPM, VTX, NLK), recorded at Suva (18.1°S, 178.5°E, L = 1.16), shows the most frequent occurrence on the NWC signal and least on the VTXνll. Daytime early/fast events on the NWC transmission are (0.2-0.5 dB) with only negative amplitude perturbations with comparatively lower recovery times (10-30 s) as compared with most nighttime events with amplitude perturbations of 0.2-1.5 dB and recovery times of 20-80 s. The World-Wide Lightning Location Network detected causative lightnings for 74 of 453 early VLF events out of which 54 (73%) were produced due to narrow-angle scattering, and by 20 (27%) due to wide-angle scattering. The recovery (decay) of the scattered amplitude of early/fast events on the NWC signal shows both exponential and logarithmic forms, but the linear correlation coefficient is better with a logarithm fit. The first observations of early/slow events in daylight propagation are presented. Initial results on early/fast events with unusually long recoveries (≥5 min) and strong perturbations (≥1 dB) indicate that they are mainly observed on the transmissions from NPM and NLK in the nighttime only, with rare occurrence on other transmissions. Such unusually long recovery of early/fast events may be associated with large ionic conductivity perturbations associated with gigantic jets.
Key words: Early VLF perturbations, D-region ionosphere, transient luminous events, scattering.


Corresponding author E-mail: sushil.kumar@usp.ac.fj


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