TITLE:
Contaminated Effect of Geomagnetic Storms on Pre-Seismic Atmospheric and Ionospheric Anomalies during Imphal Earthquake
AUTHORS:
Sagardweep Biswas, Subrata Kundu, Soujan Ghosh, Swati Chowdhury, Shih-Sian Yang, Masashi Hayakawa, Suman Chakraborty, Sandip K. Chakrabarti, Sudipta Sasmal
KEYWORDS:
Very Low Frequency, Wave Propagation, Earthquake Precursory, Atmospheric Gravity Wave, Geomagnetic Strom, SABER/TIMED
JOURNAL NAME:
Open Journal of Earthquake Research,
Vol.9 No.5,
November
12,
2020
ABSTRACT: Study of seismo-ionospheric coupling mechanism demands the quiet
geomagnetic condition to eliminate any kind of contamination in the lower
atmospheric and ionospheric parameters. In this manuscript, we present the
effect of back to back two geomagnetic storms before a strong earthquake happened
in Imphal, India on January 4, 2016 (M = 6.7).
We studied the lower ionospheric irregularities for the duration of 31 days by computing the nighttime
fluctuations in Very Low Frequency (VLF) radio signal received transmitter JJI
(22.2 kHz) in Japan at Ionospheric and Earthquake Research Centre & Optical
Observatory (IERCOO), Sitapur, India. We also studied the presence of
Atmospheric Gravity Wave (AGW) in nighttime VLF signal in lower ionospheric
heights and the same computed that from SABER/TIMED satellite. Two geomagnetic
storms occurred on December 21, and 31, 2015. By the conventional analysis, we
found that there is a significant decrease in nighttime trend and an increase
in nighttime fluctuations around 15 days before the earthquake and just on the
first storm and thus the pre-seismic effects on VLF signal gets contaminated
due to the presence of storms. The wave-like structure in VLF fluctuations
shows significant increase in intensity by using Fourier and Wavelet analysis
before the earthquake. By analysis of SABER data, we found significant
enhancement in AGW around 10 days before the earthquake. As the wavelike
structures are coming from neutral acoustics reasons from pressure or
temperature variations, this paper exhibits a significant example of
contamination in ionospheric parameters due to geomagnetic storm where the
acoustics parameters remain un-contaminated.