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Atmospheric disturbances caused by seismic activity are a complex phenomenon. The Lithosphere–Atmosphere–Ionosphere Coupling (LAIC) mechanism gives a detailed idea to understand these processes to study the possible impacts of a forthcoming earthquake. The atmospheric gravity wave (AGW) is one of the most accurate parameters for explaining such LAIC process, where seismogenic disturbances can be explained in terms of atmospheric waves caused by temperature changes. The key goal of this work is to study the perturbation in the potential energy associated with stratospheric AGW prior to many large earthquakes. We select seven large earthquakes having Richter scale magnitudes greater than seven (M > 7.0) in Japan (Tohoku and Kumamoto), Mexico (Chiapas), Nepal, and the Indian Ocean region, to study the intensification of AGW using the atmospheric temperature profile as recorded from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) satellite. We observe a significant enhancement in the potential energy of the AGW ranging from 2 to 22 days prior to different earthquakes. We examine the conditions of geomagnetic disturbances, typhoons, and thunderstorms during our study and eliminate the possible contamination due to these events. [ABSTRACT FROM AUTHOR]

Abstract: During the total solar eclipse of 2009, a week-long campaign was conducted in the Indian sub-continent to study the low-latitude D-region ionosphere using the very low frequency (VLF) signal from the Indian Navy transmitter (call sign: VTX3) operating at 18.2kHz. It was observed that in several places, the signal amplitude is enhanced while in other places the amplitude is reduced. We simulated the observational results using the well known Long Wavelength Propagation Capability (LWPC) code. As a first order approximation, the ionospheric parameters were assumed to vary according to the degree of solar obscuration on the way to the receivers. This automatically brought in non-uniformity of the ionospheric parameters along the propagation paths. We find that an assumption of 4km increase of lower ionospheric height for places going through totality in the propagation path simulate the observations very well at Kathmandu and Raiganj. We find an increase of the height parameter by km for the VTX-Malda path and km for the VTX-Kolkata path. We also present, as an example, the altitude variation of electron number density throughout the eclipse time at Raiganj. [Copyright &y& Elsevier]

We present perturbations due to seismo-ionospheric coupling processes in propagation characteristics of sub-ionospheric Very Low Frequency (VLF) signals received at Ionospheric & Earthquake Research Centre (IERC) (Lat. 22.50°N, Long. 87.48°E), India. The study is done during and prior to an earthquake of Richter scale magnitude M = 7.3 occurring at a depth of 18 km at southeast of Kodari, Nepal on 12 May 2015 at 12:35:19 IST (07:05:19 UT). The recorded VLF signal of Japanese transmitter JJI at frequency 22.2 kHz (Lat. 32.08°N, Long. 130.83°E) suffers from strong shifts in sunrise and sunset terminator times towards nighttime starting from three to four days prior to the earthquake. The signal shows a similar variation in terminator times during a major aftershock of magnitude M = 6.7 on 16 May, 2015 at 17:04:10 IST (11:34:10 UT). These shifts in terminator times is numerically modeled using Long Wavelength Propagation Capability (LWPC) Programme. The unperturbed VLF signal is simulated by using the day and night variation of reflection height ( h ′ ) and steepness parameter ( β ) fed in LWPC for the entire path. The perturbed signal is obtained by additional variation of these parameters inside the earthquake preparation zone. It is found that the shift of the terminator time towards nighttime happens only when the reflection height is increased. We also calculate electron density profile by using the Wait’s exponential formula for specified location over the propagation path. [ABSTRACT FROM AUTHOR]