Spectral Analysis and Information Entropy Approaches to Data of VLF Disturbances in the Waveguide Earth-Ionosphere

Very low frequency (VLF) signals are considered as an important tool to study ionosphere disturbances. We have studied variations in signal amplitude of the Japanese JJI transmitter received by a network of eight Japan stations. The distinctions between characteristics of daytime and nighttime distu...

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Bibliographic Details
Published in:Sensors (Basel, Switzerland) Switzerland), 2022-10, Vol.22 (21), p.8191
Main Authors: Rapoport, Yuriy, Reshetnyk, Volodymyr, Grytsai, Asen, Grimalsky, Volodymyr, Liashchuk, Oleksandr, Fedorenko, Alla, Hayakawa, Masashi, Krankowski, Andrzej, Błaszkiewicz, Leszek, Flisek, Paweł
Format: Article
Language:English
Subjects:
Analysis
Atmosphere
Atmosphere, Upper
Disturbances
Earth
Earthquakes
Entropy (Information theory)
Fourier analysis
Frequency modulation
Gravity waves
Ionosphere
Japanese VLF network
Lightning
Oscillations
Propagation
Radiation
Seasonal variations
Seismology
Shannon entropy
Signal processing
Solar flares
Sunrise
Sunset
terminator passage
VLF signal
Wave spectra
waveguide earth–ionosphere
Waveguides
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Summary:Very low frequency (VLF) signals are considered as an important tool to study ionosphere disturbances. We have studied variations in signal amplitude of the Japanese JJI transmitter received by a network of eight Japan stations. The distinctions between characteristics of daytime and nighttime disturbances are considered. Signal processing based on spectral analysis is used to evaluate typical periodicities in the VLF signals in the time range from minutes to hours. In particular, we have retrieved quasi-wave oscillations of the received signal with periods of 4–10 and 20–25 min, which can be associated with atmospheric gravity waves excited by the solar terminator, earthquakes or other reasons. In addition, oscillations at periods of 3–4 h are observed, probably, caused by long-period gravity waves. We also calculate the information entropy to identify main details in daily VLF variations and influence of solar flares. It is shown that the information entropy increases near sunrise and sunset with seasonal variation, and that solar flares also lead to the growth in information entropy. A theoretical interpretation is given to the typical features of ultra-low frequency modulation of VLF electronagnetic wave spectra in Waveguide Earth-Ionosphere, found by processing the experimental data.
ISSN:1424-8220
1424-8220
DOI:10.3390/s22218191