Anisotropic response of the near and far field ionosphere to the 2022 Hunga Tonga-Hunga Ha'apai eruption

This work presents a detailed analysis of the ionospheric response to the 2022 Hunga Tonga-Hunga Ha'apai submarine volcanic eruption in both the near (< 3500km from the source) and far fields (>9000km from the source). In particular, we investigate the co-volcanic ionospheric disturbances (CVIDs) using ground-based GNSS-TEC observations in New Caledonia-New Zealand and in Chile-Argentina. This is the first detailed study of Tonga CVIDs over South America.

The dense GNSS arrays sample different azimuthal directions with respect to the source, enabling us to study the anisotropic response of the ionosphere.

The eruption produced a great variety of atmospheric waves whose origins and characteristics are not yet fully understood.

We particularly focus on the tsunami and the tsunami-like air-sea wave signatures into the ionosphere as they are observed in the regions of this study.

In New Caledonia-New Zealand, the near-field ionosphere observations sample a succession of distinct atmospheric waves (e.g., acoustic waves, the Lamb wave, and gravity waves). We demonstrate the presence of the near-field air-sea wave, i.e., the tsunami-like wave of atmospheric origin caused by the Lamb wave coupling with the ocean.

The initial Chile-Argentina far-field ionosphere response is characterized by two main CVID patterns. The first is related to the initial passage of the Lamb wave, which also triggered small amplitude air-sea waves along the Chilean coast. We observe a good preceding of CVIDs to sea-level observations, indicating observations of the ionospheric perturbations can be observed before the air-sea wave reached the Chilean coast. The second CVID is linked to the propagation of the internal gravity wave induced by the traditional tsunami, causing coastal sea waves up to 1.7 meters in Chanaral, on the Chilean coast.

Finally, we demonstrate that ionospheric GNSS-sounding by ground-based receivers provides information about the propagation of tsunamis, including air-sea wave, especially in the far-field, and hence GNSS-TEC observations can be a complementary asset for tsunami early warning systems.