/pdf/ionospheric-detection-of-natural-hazards-39q4arpkq4.pdf

Ionospheric Detection of Natural Hazards

Upper Atmospheric Responses to Surface Disturbances: An Observational Perspective

On 15 January 2022, the Hunga Tonga-Hunga Ha’apai submarine volcano erupted violently and triggered a giant atmospheric shock wave and tsunami. The exact mechanism of this extraordinary eruptive event, its size and magnitude are not well understood yet. In this work, we analyze data from the nearest ground-based receivers of Global Navigation Satellite System to explore the ionospheric total electron content (TEC) response to this event. We show that the ionospheric response consists of a giant TEC increase followed by a strong long-lasting depletion. We observe that the explosive event of 15 January 2022 began at 04:05:54UT and consisted of at least five explosions. Based on the ionospheric TEC data, we estimate the energy released during the main major explosion to be between 9 and 37 Megatons in trinitrotoluene equivalent. This is the first detailed analysis of the eruption sequence scenario and the timeline from ionospheric TEC observations. 

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1029/2022GL098827

The 15 January 2022 Hunga Tonga Eruption History as Inferred From Ionospheric Observations

The explosive eruption of the Hunga-Tonga volcano in the southwest Pacific at 0415UT on 15 January 2022 triggered gigantic atmospheric disturbances with surface air pressure waves propagating around the globe in Lamb mode. In space, concentric traveling ionosphere disturbances (CTIDs) are also observed as a manifestation of air pressure waves in New Zealand ∼0500UT and Australia ∼0630UT. As soon as the air pressure waves reached central Australia ∼0800UT, conjugate CTIDs appeared almost simultaneously in the northern hemispheres through interhemispheric coupling, much earlier than the arrival of the surface air pressure waves to Japan after 1100UT. Combining observations over Australia and Japan between 0800 and 1000UT, both direct and conjugate CTIDs show similar horizontal phase velocities of 320–390 m/s, matching with the dispersion relation of Lamb mode. The arrival of atmospheric Lamb wave to Japan later created in situ CTIDs showing the same Lamb mode characteristics as the earlier conjugate CTIDs. 

Rapid Conjugate Appearance of the Giant Ionospheric Lamb Wave Signatures in the Northern Hemisphere After Hunga‐Tonga Volcano Eruptions

The two major explosive phases of the 22–23 April 2015 eruption of Calbuco volcano, Chile produced powerful seismicity and infrasound. The eruption was recorded on seismo-acoustic stations out to 1,540 km and on 5 stations (IS02, IS08, IS09, IS27, and IS49) of the International Monitoring System (IMS) infrasound network at distances from 1,525 to 5,122 km. The remote IMS infrasound stations provide an accurate explosion chronology consistent with the regional and local seismo-acoustic data, and with previous studies of lightning and plume observations. We use the IMS network to detect and locate the eruption signals using a brute-force, grid-search, cross-bearings approach. After incorporating azimuth deviation corrections from stratospheric cross-winds using 3D ray-tracing, the estimated source location is 172 km from true. This case study highlights the significant capability of the IMS infrasound network to provide automated detection, characterization, and timing estimates of global explosive volcanic activity. Augmenting the IMS with regional seismo-acoustic networks will dramatically enhance volcanic signal detection, reduce latency, and improve discrimination capability.

/pdf/local-regional-and-remote-seismo-acoustic-observations-of-bkuexdldf5.pdf

Local, Regional, and Remote Seismo‐Acoustic Observations of the April 2015 VEI 4 Eruption of Calbuco Volcano, Chile

Using data from ground-based GNSS-receivers located in southern Chile, we study the ionospheric total electron content (TEC) response to two eruptions of the Calbuco volcano that occurred on 22-23 April 2015. In both cases, the TEC response showed quasi-periodic signals with several consecutive wave-trains. The averaged amplitude of the observed co-volcanic TEC-perturbations amounted 0.45 TECU for the first eruption and 0.16 TECU for the second one. We compare amplitudes of the TEC response to volcano eruptions of different intensity from our and previously published data, and we show that both the intensity and the background ionospheric conditions define the amplitude of ionospheric co-volcanic disturbances (CVID). The relative contribution, however, scales with the eruption intensity.

The travel-time diagrams allowed to estimate the propagation speed of the observed co-volcanic TEC perturbations as ~900-1200 m/s, which is close to the acoustic (or shock-acoustic) waves speed at the ionospheric height. The spectrograms are consistent with the conclusion on the acoustic nature of the observed TEC perturbations.

Finally, we use the approximation of a spherical wave propagating at a constant velocity from a point source and, for the first time, we calculate the location of the volcanic source and the onset time of the volcano eruption from ionospheric measurements. We show that even from 30-sec ionospheric GPS data it is possible to “localize” the eruptive source within several degrees of latitude/longitude.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2016JA023382

Ionospheric detection and localization of volcano eruptions on the example of the April 2015 Calbuco events


 In previous publications, we presented a general framework, which we called “box tomography”, that allows the coupling of any two different numerical seismic wave propagation solvers, respectively outside and inside a target region, or “box”. The goal of such hybrid wavefield computations is to reduce the cost of computations in the context of full-waveform inversion for structure within the target region, when sources and/or receivers are located at large distances from the box. Previously, we had demonstrated this approach with sources and receivers outside the target region in a 2D acoustic spherical earth model, and demonstrated and applied this methodology in the 3D spherical elastic earth in a continental scale inversion in which all stations were inside the target region. Here we extend the implementation of the approach to the case of a 3D global elastic earth model in the case where both sources and stations are outside the box. We couple a global 3D solver, SPECFEM3D_GLOBE, for the computation of the wavefield and Green’s functions in a reference 3D model, with a regional 3D solver, RegSEM, for the computation of the wavefield within the box, by means of time-reversal mirrors. We briefly review key theoretical aspects, showing in particular how only the displacement is needed to be stored at the boundary of the box. We provide details of the practical implementation, including the geometrical design of the mirrors, how we deal with different sizes of meshes in the two solvers, and how we address memory-saving through the use of B-spline compression of the recorded wavefield on the mirror. The proposed approach is numerically efficient but also versatile, since adapting it to other solvers is straightforward and does not require any changes in the solver codes themselves, as long as the displacement can be recovered at any point in time and space. We present benchmarks of the hybrid computations against direct computations of the wavefield between a source and an array of stations in a realistic geometry centered in the Yellowstone region, with and without a hypothetical plume within the “box”, and with a 1D or a 3D background model, down to a period of 20 seconds. The ultimate goal of this development is for applications in the context of imaging of remote target regions in the deep mantle, such as, for example, Ultra Low Velocity Zones.

Sevan Adourian

Papers

Ionospheric detection and localization of volcano eruptions on the example of the April 2015 Calbuco events

Combining different 3D global and regional seismic wave propagation solvers towards box tomography in the deep Earth