Geomagnetic Detection of the Atmospheric Acoustic Resonance at 3.8 mHz During the Hunga Tonga Eruption Event on 15 January 2022

Abstract

Geophysical events such as earthquakes, volcanoes and tsunamis can cause atmospheric waves such as acoustic waves and gravity waves (Yeh & Liu, 1974). Acoustic waves have frequencies higher than the acoustic cutoff frequency (∼3.2 mHz at the stratopause), while gravity waves have frequencies lower than the Brunt-Väisälä frequency (∼2.7 mHz at the stratopause). They can propagate away from the source, transferring energy and momentum into the middle and upper atmosphere. As the waves propagate to higher altitudes, they grow in amplitude due to decreasing atmospheric density. Yeh and Liu (1974) estimated that a seismic wave with vertical ground displacement of 5 mm could lead to an acoustic wave whose vertical wind velocity reaches 30 m/s at an altitude of 150 km. Such a large perturbation of the neutral atmosphere would have a significant impact on the dynamics and electrodynamics of the ionosphere. Indeed, ionospheric disturbances associated with acoustic and gravity waves have been reported following strong earthquakes and other geophysical events for many decades (see reviews by e.g., Astafyeva, 2019;Meng et al., 2019).Atmospheric oscillations with frequencies near the acoustic cutoff frequency are frequently observed after eruption events (Kanamori et al., 1994). Modeling studies have shown that those oscillations can be explained by acoustic waves trapped between the ground and thermosphere (e.g.

Rapid Volcanic Modification of the E‐Region Dynamo: ICON's First Glimpse of the Tonga Eruption

“…These observations are also clear evidence of a conjugate effect: electric fields established by wind-driven currents in the vicinity of the volcano were transported to the observatory's location via Alfvén waves, and arrived much sooner than any reported atmospheric waves. This observation and interpretation supports previous reports of conjugate effects due to this event (Iyemori et al, 2022;Lin et al, 2022;Shinbori et al, 2022;Yamazaki et al, 2022).…”

“…Yamazaki et al. (2022) and Iyemori et al. (2022) reported surface geomagnetic field variations shortly after the eruption both at a site ∼835 km from Tonga, and in Honolulu, Hawaii, which is near Tonga's geomagnetic conjugate point.…”

“…Based on numerical modeling results by Zettergren and Snively (2019), Yamazaki et al. (2022) suggested that the observed geomagnetic field variations were signatures of ionospheric dynamo currents driven by neutral wind variations caused by the volcano. Using Super Dual Auroral Radar Network radar observations, Shinbori et al.…”

“…TEC disturbances can result from a variety of mechanisms, including field-aligned drag, dynamo electric fields, and composition changes, but studies using TEC data alone are often unable to distinguish between these mechanisms. Yamazaki et al (2022) and Iyemori et al (2022) reported surface geomagnetic field variations shortly after the eruption both at a site ∼835 km from Tonga, and in Honolulu, Hawaii, which is near Tonga's geomagnetic conjugate point. Based on numerical modeling results by Zettergren and Snively (2019), Yamazaki et al (2022) suggested that the observed geomagnetic field variations were signatures of ionospheric dynamo currents driven by neutral wind variations caused by the volcano.…”

“…Yamazaki et al (2022) and Iyemori et al (2022) reported surface geomagnetic field variations shortly after the eruption both at a site ∼835 km from Tonga, and in Honolulu, Hawaii, which is near Tonga's geomagnetic conjugate point. Based on numerical modeling results by Zettergren and Snively (2019), Yamazaki et al (2022) suggested that the observed geomagnetic field variations were signatures of ionospheric dynamo currents driven by neutral wind variations caused by the volcano. Using Super Dual Auroral Radar Network radar observations, Shinbori et al (2022) reported meridional plasma drift variations with ∼100 m/s amplitude in the conjugate hemisphere shortly after the Tonga eruption.…”