GNSS-Derived Ionospheric Observations From the January 13-15 Tonga Eruptions and Tsunamis Over the Southwestern Pacific

The eruptions of Hunga Tonga-Hunga Ha'apai (HTHH) on 13-15 January 2022 generated waves in the atmosphere and ocean that were detectable as disturbances in Earth's ionosphere. These Traveling Ionospheric Disturbances (TIDs) offer valuable information about acoustic and tsunami waves produced during the Tonga event. In the past decade, the use of Global Navigation Satellite Systems (GNSS) data has increasingly been utilized to explore ionospheric activity during natural hazard events. Many studies on this eruption sequence have focused on the climactic eruption and tsunami on 15 January or have highlighted the global reach of their TIDs. Given the complexities that arise due to wave-guiding, ocean bathymetry, and interference, we instead focus our analysis on TIDs over the southwestern Pacific and consider the full eruption sequence. Specifically, we use GNSS to explore the superpositioning and separation of acoustic- and tsunami-generated TIDs within ~3500 km of HTHH during 13-15 January. To do this, GNSS data were gathered from 818 stations managed by UNAVCO, IGS, Geoscience Australia, and GNS New Zealand. Raw data were processed using the SNIVEL_ION algorithm, while filtered time series were manually inspected to remove gross outliers. Lastly, tsunami arrivals were validated using DART (Deep-Ocean Assessment and Reporting of Tsunamis) buoy data where available. We find notably larger TIDs on 15 January, with perturbations up to ~7 TECu. Furthermore, we detect supersonic TIDs traveling at 833 m/s, with Lamb wave- and tsunami-generated TIDs following at 310 m/s. We also note a faster tsunami-generated TID that travels at 463 m/s, with a shift in the frequency domain, that crosses the slower TIDs ~3000 km from HTHH. Back-propagation shows that it took one hour for this faster TID to generate after the main eruption. We find that acoustic- and tsunami-generated TIDs begin to separate from each other at ~1000 km from HTHH and are distinct by ~2200 km from the source. Finally, we consider self-similarity between ionospheric signatures on the 13th and 15th to extract differences in the eruption history.