Nonlinear acoustic waves in the viscous thermosphere and ionosphere above earthquake

Abstract

The nonlinear behavior of acoustic waves and their dissipation in the upper atmosphere is studied on the example of infrasound waves generated by vertical motion of the ground surface during the Mw 8.3 earthquake that occurred about 46 km from Illapel, Chile on 16 September 2015. To conserve energy, the amplitude of infrasound waves initially increased as the waves propagated upward to the rarefied air. When the velocities of air particles became comparable with the local sound speed, the nonlinear effects started to play an important role. Consequently, the shape of waveform changed significantly with increasing height, and the original wave packet transformed to the “N‐shaped” pulse resembling a shock wave. A unique observation by the continuous Doppler sounder at the altitude of about 195 km is in good agreement with full wave numerical simulation that uses as boundary condition the measured vertical motion of the ground surface.

Physics‐Based Modeling of Earthquake‐Induced Ionospheric Disturbances

“…As these waves propagate through the atmosphere, they experience attenuation due to atmospheric viscosity. Both the nonisothermal and viscous effects have been considered by Kherani et al (), Rolland et al (), Zettergren and Snively (), Chum et al (), and Rakoto et al (). In addition, Kherani et al () has also included the background wind in their model.…”

“…Specifically, we focus on ionospheric responses to acoustic‐gravity waves induced by the crustal movement at an epicentral zone rather than the Rayleigh surface wave or seismic air wave‐related ionospheric signatures, which will be addressed in the future. The new WP‐GITM is capable of being driven by actual seismic measurements of ground motions, representing another unique feature that distinguishes our work from previous modeling efforts, excluding Chum et al ().…”

“…A follow‐up study by Zettergren et al () applied the same 2‐D modeling approach to an earthquake with an analytical source and reproduced observed TEC depletions near the epicenter. Chum et al () developed a one‐dimensional nonlinear model driven by seismic measurements to simulate air particle velocity perturbations in the upper atmosphere and found good agreement between the simulation and Doppler sounder observations. In addition, there are models dedicated to tsunami‐ionosphere coupling yet can be directly applied to earthquake‐ionosphere coupling.…”

Geomagnetic conjugate observations of ionospheric disturbances in response to a North Korean underground nuclear explosion on 3 September 2017

“…Klimenko et al (2011) proposed that the ionospheric disturbances were generated by small-scale internal gravity waves (IGWs) through propagation and dissipation processes during seismic activity. Liu et al (2016), and Chum et al (2016Chum et al ( , 2018 suggested that coseismic ionospheric disturbances could be generated by longperiod infrasound waves excited by seismic waves. Based on GNSS receiver observations over the Brazilian sector, Jonah et al (2017) presented daytime medium-scale traveling ionospheric disturbances (MSTIDs) observed in the conjugate hemispheres.…”

Characterizing Coseismic Ionospheric Disturbance for Surface-Rupturing Earthquakes

“…When the velocity of air particles becomes close to the speed of sound a "shockacoustic" effect occurs (Afraimovich et al, 2001) due to non-linear effects (Chum et al, 2016). Large earthquakes produce acoustic waves that approach the speed of sound and thus the original waveform is transformed into an N-shaped wave.…”