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Contaminated Effect of Geomagnetic Storms on Pre-Seismic Atmospheric and Ionospheric Anomalies during Imphal Earthquake

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Document pages: 20 pages

Abstract: Study of seismo-ionospheric coupling mechanism demands the quietgeomagnetic condition to eliminate any kind of contamination in the loweratmospheric and ionospheric parameters. In this manuscript, we present theeffect of back to back two geomagnetic storms before a strong earthquake happenedin Imphal, India on January 4, 2016 (M = 6.7).We studied the lower ionospheric irregularities for the duration of 31 days by computing the nighttimefluctuations in Very Low Frequency (VLF) radio signal received transmitter JJI(22.2 kHz) in Japan at Ionospheric and Earthquake Research Centre & OpticalObservatory (IERCOO), Sitapur, India. We also studied the presence ofAtmospheric Gravity Wave (AGW) in nighttime VLF signal in lower ionosphericheights and the same computed that from SABER TIMED satellite. Two geomagneticstorms occurred on December 21, and 31, 2015. By the conventional analysis, wefound that there is a significant decrease in nighttime trend and an increasein nighttime fluctuations around 15 days before the earthquake and just on thefirst storm and thus the pre-seismic effects on VLF signal gets contaminateddue to the presence of storms. The wave-like structure in VLF fluctuationsshows significant increase in intensity by using Fourier and Wavelet analysisbefore the earthquake. By analysis of SABER data, we found significantenhancement in AGW around 10 days before the earthquake. As the wavelikestructures are coming from neutral acoustics reasons from pressure ortemperature variations, this paper exhibits a significant example ofcontamination in ionospheric parameters due to geomagnetic storm where theacoustics parameters remain un-contaminated.

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