Modeling of ionospheric magnetic field perturbations induced by earthquakes

Abstract

[1] The objective of this study is to present a simple coupled seismo-ionospheric model to account for magnetic field perturbations in response to geophysical phenomena such as Earthquakes or tsunamis. For this purpose, we include a simple gravity wave model in the two dimensional mid latitude ionosphere model SAMI2. Following an earthquake, the disturbances in the neutral atmosphere density and velocity associated with gravity waves propagate vertically upward up to ionospheric altitudes 150-350 km, where significant coupling between the neutral atmosphere and the ionosphere occurs. As a result, a rapid variation in the ionospheric plasma density and temperature is observed associated with the photoionization of the perturbed neutral density. This variation in the electron density leads in turn to a variation in the total electron content (TEC). Strong variations in the TEC are observed close to the epicenter which correspond to large plasma density perturbations in this region associated with the ion acoustic mode. The calculation of magnetic perturbations is based on a set of reduced MHD equations. These are solved numerically using the finite element code TOPO coupled with the mid latitude ionospheric model SAMI2. The coupling between the two codes accounts for the variations in neutral gas density and the collisional drag force between ions and neutrals. Two wave modes are considered: the shear Alfvén mode and the compressional mode. The results of the magnetic field perturbations and of ions' velocity perturbations associated with the shear Alfvén and the compressional modes are presented. Variations in the TEC values are also computed for the compressional mode by taking into account the density perturbations transverse to the magnetic field. The results representing TEC perturbations associated with the compressional mode show strong variations at high latitudes both as a function of time and latitude.

Ionospheric signatures of acoustic waves generated by transient tropospheric forcing

“…More directive sources, yielding waves with approximately planar phase fronts, may produce TEC responses with a different character [e.g., Imtiaz and Marchand, 2012]. Electron density fluctuations in the source hemisphere are 10% and large enough to be observable via high time and range resolution incoherent scatter radar experiments [e.g., Djuth et al, 2010]; no significant electron signatures are present in the conjugate hemispheres.…”

Teleseismic magnetic effects (TMDs) of 2011 Tohoku earthquake

“…So far, models on coupling energy from Earth's surface vibrations to the ionosphere have been established to confirm the interaction among spheres and simulate both seismo‐induced neutral atmospheric waves and therefore ionospheric variations [ Artru et al ., , ; Watada et al ., ; Rolland et al ., ]. Recently, Imtiaz and Marchand [] present a model to account for magnetic field perturbation, when given an acoustic impulse in the atmosphere. But no model has been completed so far to simulate the whole coupling system, from seismic waves to the magnetic disturbances.…”

Latitude and Longitude Dependence of Ionospheric TEC and Magnetic Perturbations From Infrasonic‐Acoustic Waves Generated by Strong Seismic Events

“…AGWs generate dynamo electrical currents and, hence, magnetic perturbations, as they propagate through conducting ionospheric plasma layers at ∼100–300‐km altitude (e.g., Hao et al, ; Zettergren & Snively, , ). Simulations of magnetic fluctuations due to seismic sources predict detectable fluctuations at AGW frequencies at ground‐level (Kherani et al, ) and in the ionosphere (Imtiaz & Marchand, ). Detailed simulations by Zettergren and Snively () found ground‐level signatures ∼0.1–2 nT in amplitude and in situ signatures are ∼1–10 nT, which match the approximate characteristics of observations; however, simplified sources and two‐dimensional (2‐D) models were used that do not fully capture the geometry of wave‐driven currents.…”