Author(s)

Sagardweep Biswas^1*, Subrata Kundu¹, Soujan Ghosh¹, Swati Chowdhury¹, Shih-Sian Yang², Masashi Hayakawa³, Suman Chakraborty⁴, Sandip K. Chakrabarti¹, Sudipta Sasmal¹

¹Indian Centre for Space Physics, Kolkata, India.
²Institute of Space Science, National Central University, Chinese Taipei.
³Hayakawa Institute of Seismo Electromagnetics Co. Ltd., UEC Alliance Center, Chofu, Tokyo, Japan.
⁴Physical Research Laboratory, Navrangpura, Ahmedabad, India.

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.

Very Low Frequency, Wave Propagation, Earthquake Precursory, Atmospheric Gravity Wave, Geomagnetic Strom, SABER/TIMED

Biswas, S. , Kundu, S. , Ghosh, S. , Chowdhury, S. , Yang, S. , Hayakawa, M. , Chakraborty, S. , K. Chakrabarti, S. and Sasmal, S. (2020) Contaminated Effect of Geomagnetic Storms on Pre-Seismic Atmospheric and Ionospheric Anomalies during Imphal Earthquake. Open Journal of Earthquake Research, 9, 383-402. doi: 10.4236/ojer.2020.95022.