Ionospheric response to infrasonic‐acoustic waves generated by natural hazard events

Abstract

Recent measurements of GPS‐derived total electron content (TEC) reveal acoustic wave periods of ∼1–4 min in the F region ionosphere following natural hazard events, such as earthquakes, severe weather, and volcanoes. Here we simulate the ionospheric responses to infrasonic‐acoustic waves, generated by vertical accelerations at the Earth's surface or within the lower atmosphere, using a compressible atmospheric dynamics model to perturb a multifluid ionospheric model. Response dependencies on wave source geometry and spectrum are investigated at middle, low, and equatorial latitudes. Results suggest constraints on wave amplitudes that are consistent with observations and that provide insight on the geographical variability of TEC signatures and their dependence on the geometry of wave velocity field perturbations relative to the ambient geomagnetic field. Asymmetries of responses poleward and equatorward from the wave sources indicate that electron perturbations are enhanced on the equatorward side while field aligned currents are driven principally on the poleward side, due to alignments of acoustic wave velocities parallel and perpendicular to field lines, respectively. Acoustic‐wave‐driven TEC perturbations are shown to have periods of ∼3–4 min, which are consistent with the fraction of the spectrum that remains following strong dissipation throughout the thermosphere. Furthermore, thermospheric acoustic waves couple with ion sound waves throughout the F region and topside ionosphere, driving plasma disturbances with similar periods and faster phase speeds. The associated magnetic perturbations of the simulated waves are calculated to be observable and may provide new observational insight in addition to that provided by GPS TEC measurements.

Localized field-aligned currents and 4-min TEC and ground magnetic oscillations during the 2015 eruption of Chile’s Calbuco volcano

“…3b, which corresponds to zonal component of magnetic perturbations, is largest. This is consistent with Figure 8c in Zettergren and Snively (2015) and Figure 14 in Nakanishi et al (2014). The difference of the amplitude between δB y in our Fig.…”

“…As to the theoretical study, TEC oscillations observed after the 2011 off the Pacific coast of Tohoku Earthquake and FACs in the ionosphere generated by acoustic mode waves were well reproduced with numerical simulations by Matsumura et al (2011) and by Zettergren and Snively (2013), respectively. Zettergren and Snively (2015) performed the computer simulations showing that TEC and ground-level magnetic field perturbations and dynamo FACs can be caused by natural hazard events including volcanic eruptions.…”

Modifications of the ionosphere prior to large earthquakes: report from the Ionosphere Precursor Study Group

“…The role of AGWs has been discussed by Klimenko et al (2011), who attributed the NmF2 increase to a change in the neutral composition. Very recently, the ionospheric response to infrasonic acoustic waves generated by natural hazard events has been reported (Zettergren and Snively 2013). Their computer simulations seem to support the idea that no clear disturbance appears directly above the epicenter.…”

Ground-based acoustic parametric generator impact on the atmosphere and ionosphere in an active experiment

“…Acoustic waves also drive field-aligned currents that may be detectable by in situ magnetometers (Iyemori et al, 2015). A recent paper (Zettergren and Snively, 2015) reports that the recent measurements of GPS-derived TEC reveals acoustic wave periods from ∼ 1 to 4 min in the F-region ionosphere following natural hazard events, such as earthquakes, severe weather fronts, and volcanoes.…”

“…Moreover, in order to search the seismogenic effects in the ionosphere, it is necessary to unify the well-developed model of the electromagnetic channel to seismo-ionospheric coupling (Molchanov et al, 1995;Rapoport et al, 2004b;Grimalsky et al, 1999;Pulinets and Boyarchuk, 2004;Sorokin and Hayakawa, 2013) with the model of the acoustic channel (Gokhberg and Shalimov, 2000;Rapoport et al, 2004aRapoport et al, , 2009Koshevaya et al, 2002;Grimalsky et al, 2003;Zettergren and Snively, 2015;Iyemori et al, 2015). Traditionally, AGWs and electromagnetic waves have been considered as the basis of two main competitive mechanisms of seismo-ionospheric coupling (Sorokin and Hayakawa, 2013;Klimenko et al, 2011;Pulinets and Boyarchuk, 2004).…”