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

Abstract

A numerical study of the effects of seismically generated acoustic waves in the ionosphere is conducted using a three‐dimensional (3‐D) ionospheric model driven by an axisymmetric neutral atmospheric model. A source consistent with the 2011 Tohoku earthquake initial ocean surface uplifting is applied to simulate the subsequent responses. Perturbations in electron density, ion drift, total electron content (TEC), and ground‐level magnetic fields are examined. Results reveal strong latitude and longitude dependence of ionospheric TEC, and of ground‐level magnetic field perturbations associated with acoustic wave‐driven ionospheric dynamo currents. Results also demonstrate that prior two‐dimensional models can capture dominant meridional responses of TEC over latitude, even though dynamics at other longitudes are not resolved. Conclusions support that TEC and magnetic signatures can arise from nonlinear acoustic waves generated by strong earthquakes; simulations elucidate the comprehensive physics of their 3‐D ionospheric responses.

Modeling of Ionospheric Responses to Atmospheric Acoustic and Gravity Waves Driven by the 2015 Nepal 7.8 Gorkha Earthquake

“…Its magnitude is 0.15–0.17 TECu and comparable with magnitudes presented in past observational reports (Masashi et al, ; Tulasi Ram et al, ) and with results of our analysis in section . The magnitude is small, in comparison, for example, with the 2011 Tohoku 9.1 earthquake, where AGWs drove a TEC depletion of 4–5 TECu (Saito et al, ; Zettergren & Snively, ; Zettergren et al, ). We assume that this is due to the much smaller amplitudes of AGWs for the Nepal earthquake.…”

“…The GEMINI model solves the conservation equations (mass, momentum, and energy) for each major ionospheric species ( = O , NO , N , O , N , H ) with an electrostatic description of dynamo currents based on the five‐moment approximation (Schunk & Nagy, ; Zettergren & Semeter, ; Zettergren & Snively, ). A tilted dipole coordinate system is used as a generalized orthogonal coordinate system (Huba et al, ).…”

“…Zettergren et al () reported simulations of nonlinear AGWs effects, including plasma depletion “holes” (the decrease of absolute electron density that is persistent over multiple oscillations from the propagation of AWs and conducted by comparatively long‐period recovering phase), after the 2011 9.0 Tohoku‐oki earthquake using an axisymmetric source based on initial ocean surface displacement data. For the same event Zettergren and Snively () presented results of TEC and magnetic field fluctuations driven by the same AGW sources with a new 3‐D multifluid‐electrodynamic ionospheric model (GEMINI 3D).…”

Numerical Modeling of the Propagation of Infrasonic Acoustic Waves Through the Turbulent Field Generated by the Breaking of Mountain Gravity Waves

“…Second, a qualitative analysis of the effects of small‐scale turbulent fluctuations on ground recordings is carried out, to provide a preliminary and nonexhaustive answer to the fundamental question of predictability of infrasonic arrivals. This demonstrates and motivates a pathway toward more comprehensive and quantitative 3‐D investigations of the interactions between IAWs and turbulent atmospheric dynamics (including both 2‐D and 3‐D cascades, as well as oblique propagation of IAWs and GWs) and of the subsequent effects on signals recorded at the ground, in the stratosphere (Bowman & Lees, ), or in the thermosphere‐ionosphere (Zettergren & Snively, ).…”

“…In the last three decades, numerous studies on the propagation and breaking of GWs generated by different sources have been conducted by performing 2‐D and 3‐D simulations of the Navier‐Stokes equations (e.g., Fritts & Alexander, ; Snively & Pasko, , and references therein). The use of the full set of the fluid dynamic equations to investigate the 2‐D and 3‐D propagation of IAWs is a relatively recent subject of research, made feasible by advances of computational capabilities (de Groot‐Hedlin, , , ; Marsden et al, ; Sabatini et al, , ; Zettergren & Snively, , ). In this work, the propagation of an IAW through the small‐scale inhomogeneities induced by the breaking of a MW is analyzed by direct numerical simulations of the 2‐D Navier‐Stokes equations.…”