One-day analysis of natural sound via very low frequency signal from Malaysian ionosphere

Abstract

This paper presents findings on the impact of lightning discharges on very low frequency (VLF) signal, which falls from 30 Hz up to 50 kHz has been used effectively for space parameter detection of the lower ionosphere signal propagation over Malaysia. Using a VLF line receiver installed at Universiti Kebangsaan Malaysia (Latitude 2° 55' N, Longitude 101° 46' E), observations conducted on 22 July 2009 revealed distinct diurnal variations. During the daytime, broadband and narrowband data were analyzed to investigate natural radio signals from transmitters in neighboring countries such as India, Japan, China, and Australia. The results reveal significant perturbations in VLF signal propagation caused by lightning discharges, leading to the detection of natural sferics, tweeks, and ionospheric disturbances. These phenomena, originating from radiated lightning discharge activity, were found to average 44 occurrences per hour during the afternoon and evening. The study highlights how these natural electromagnetic events contribute to amplitude and phase variations in VLF signals, offering deeper insights into ionospheric interactions with lightning activity. Additionally, the findings emphasize the presence of natural radio emissions such as sferics and their components, which further illustrate the effect of lightning discharges on the lower ionosphere above Malaysia.