Simulating the dependence of seismo-ionospheric coupling on the magnetic field inclination

Abstract

Abstract. Infrasound generated during a seismic event upon reaching the ionospheric heights possesses the ability to perturb the ionosphere. Detailed modelling investigation considering 1-D dissipative linear dynamics, however, indicates that the magnitude of ionospheric perturbation strongly depends on the magnetic field inclination. Physics-based SAMI2 model codes have been utilized to simulate the ionosphere perturbations that are generated due to the action of the vertical wind perturbations associated with the seismic infrasound. The propagation of the seismic energy and the vertical wind perturbations associated with the infrasound in the model has been considered to be symmetric about the epicentre in the north-south directions. Ionospheric response to the infrasound wind, however, has been highly asymmetric in the model simulation in the north-south directions. This strong asymmetry is related to the variation in the inclination of the Earth's magnetic field north and south of the epicentre. Ionospheric monitoring generally provides an efficient tool to infer the crustal propagation of the seismic energy. However, the results presented in this paper indicate that the mapping between the crustal process and the ionospheric response is not a linear one. These results also imply that the lithospheric behaviour during a seismic event over a wide zone in low latitudes can be estimated through ionospheric imaging only after factoring in the magnetic field geometry.Keywords. Atmospheric composition and structure (pressure density and temperature) -history of geophysics (atmospheric sciences) -ionosphere (ionosphere-atmosphere interactions)

On the Co‐Seismic Ionospheric Disturbances (CIDs) in the Rapid Run Ionosonde Observations Over Allahabad Following Mw 7.8 Nepal Earthquake on April 25, 2015

“…It is found one-to-one correspondence between Doppler signal and seismic waves (e.g., Yuen et al, 1969). Catherine et al (2017) also have investigated the Nepal earthquake using GPS TEC observations and suggested that these Rayleigh wave induced acoustic waves are not propagated to northern latitudes but they propagated to southern latitudes which is in agreement with Reddy and Gopi (2015) but in contrast to Joshi et al (2017) modeling work. This can be overcome by using rapid run ionograms (high resolution) to study the infrasonic wave signatures in the ionograms.…”

“…However, Doppler shift of the HF radar system can't provide altitude information as it is limited by its operating frequency. But Joshi et al (2017) has considered that rupture is uniform in the north and south direction. The high resolution ionosonde observations as presented above show wave perturbations possibly linked to acoustic and atmospheric gravity waves during the time of earthquake.…”

“…The ionospheric disturbance which are excited by Rayleigh surface waves propagate with velocity of 3.3 km/s. But SAMI2 simulations showed that ionospheric response can be asymmetric due to the changes in the inclination angle of the Earth's magnetic field that causes more wave perturbation in the northern side than southern side of the epicenter even though symmetric wave propagation on north-south direction is assumed (Joshi et al, 2017). It is believed that ionospheric density can be perturbed by three processes during earthquakes namely (a) acoustic gravity wave modulating the E region electric fields which in turn modify the F region density through E region dynamo, (b) direct penetration of acoustic waves into the F region to produce density perturbation and (c) density modulations observed at E region altitudes (e.g., Choosakul et al, 2009).…”

“…Sunil et al (2017), on the other hand, suggested that one of the reasons for this asymmetry could be due to coupling of earth's magnetic field with the acoustic wave. But SAMI2 simulations showed that ionospheric response can be asymmetric due to the changes in the inclination angle of the Earth's magnetic field that causes more wave perturbation in the northern side than southern side of the epicenter even though symmetric wave propagation on north-south direction is assumed (Joshi et al, 2017). Maruyama et al (2012) have investigated many ionograms at different stations during the time of earthquake and suggested that Rayleigh wave and acoustic wave signatures can be detected in the ionograms in the form of Multiple Cusp Signatures (MCS) in the ionograms.…”

“…Sunil et al (2017), on the other hand, suggested that one of the reasons for this asymmetry could be due to coupling of earth's magnetic field with the acoustic wave. But SAMI2 simulations showed that ionospheric response can be asymmetric due to the changes in the inclination angle of the Earth's magnetic field that causes more wave perturbation in the northern side than southern side of the epicenter even though symmetric wave propagation on north-south direction is assumed (Joshi et al, 2017). Maruyama et al…”