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SUMMARY The eruption of the submarine Hunga Tonga-Hunga Haʻapai (Hunga Tonga) volcano on 15 January 2022, was one of the largest volcanic explosions recorded by modern geophysical instrumentation. The eruption was notable for the broad range of atmospheric wave phenomena it generated and for their unusual coupling with the oceans and solid Earth. The event was recorded worldwide across the Global Seismographic Network (GSN) by seismometers, microbarographs and infrasound sensors. The broad-band instrumentation in the GSN allows us to make high fidelity observations of spheroidal solid Earth normal modes from this event at frequencies near 3.7 and 4.4 mHz. Similar normal mode excitations were reported following the 1991 Pinatubo (Volcanic Explosivity Index of 6) eruption and were predicted, by theory, to arise from the excitation of mesosphere-scale acoustic modes of the atmosphere coupling with the solid Earth. Here, we compare observations for the Hunga Tonga and Pinatubo eruptions and find that both strongly excited the solid Earth normal mode 0S29 (3.72 mHz). However, the mean modal amplitude was roughly 11 times larger for the 2022 Hunga Tonga eruption. Estimates of attenuation (Q) for 0S29 across the GSN from temporal modal decay give Q = 332 ± 101, which is higher than estimates of Q for this mode using earthquake data (Q = 186.9 ± 5). Two microbarographs located at regional distances (<1000 km) to the volcano provide direct observations of the fundamental acoustic mode of the atmosphere. These pressure oscillations, first observed approximately 40 min after the onset of the eruption, are in phase with the seismic Rayleigh wave excitation and are recorded only by microbarographs in proximity (<1500 km) to the eruption. We infer that excitation of fundamental atmospheric modes occurs within a limited area close to the site of the eruption, where they excite select solid Earth fundamental spheroidal modes of similar frequencies that are globally recorded and have a higher apparent Q due to the extended duration of atmospheric oscillations.
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Resonance excitation of atmospheric waves by vibration of the ground, ocean surface, and ice shelves
Atmosphere is known to respond in a resonant way to broad-band excitation associated with earthquakes, volcano eruptions, and convective storms. The resonances are observed via their ionospheric manifestations using HF Doppler radars, airglow observations, and the GPS-TEC technique and are seen as narrow frequency bands of greatly amplified oscillations. The resonances are normal modes of an atmospheric waveguide and occur at such frequencies that an acoustic-gravity wave, which is radiated at the ground level and is reflected from a turning point in the thermosphere or upper mesosphere, upon return to the ground level satisfies boundary conditions on the ground. Typically, the resonances correspond to near-vertical AGW propagation and have periods of about 3–5 minutes. Although the resonances are usually referred to as acoustic resonances, buoyancy effects are not negligible at such frequencies. The resonances correspond to most efficient coupling between atmosphere and its lower boundary and are promising for detection of such coupling. From the remote sensing prospective, the resonances are potentially significant because their frequencies are sensitive to variations in the vertical profile of neutral temperature up to thermospheric altitudes and to boundary conditions on the lower boundary, such as differences between the boundary conditions on the solid earth, ocean surface, and a finite ice layer overlying solid Earth or the ocean. Using recently developed consistent WKB approximation for acoustic-gravity waves, this paper investigates theoretically excitation of atmospheric resonances and quantifies the effects of buoyancy and non-vertical propagation, including the contribution of the Berry phase. Different kinds of atmospheric resonances are identified depending on the type of surface waves, including flexural waves in ice shelves, that are responsible for oscillations at the ground or sea level.
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- Award ID(s):
- 1643119
- PAR ID:
- 10282360
- Date Published:
- Journal Name:
- Geophysical research abstracts
- Volume:
- 20
- ISSN:
- 1607-7962
- Page Range / eLocation ID:
- 5584
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/EGU2018/EGU2018-5584
