The AIR team just released a new preprint Stratospheric balloon observations of infrasound from the 2021-2022 Hunga eruptive sequence and its 19 December 2021 eruption (Hardy et al., 2026)! In this contribution we re-analyze balloon data during the early and later stages of the major 2022 Honga Tonga eruption sequence. We found previously un-detected signals on ground stations from the December eruptions. We also highlight the importance of plume dynamics and plume height on infrasound production.
Balloon-borne infrasound monitoring has undergone a revival over the past decade, driven by technological advances that enable high-sensitivity, low-noise acoustic recordings from air-borne platforms. The cataclysmic 15 January 2022 Hunga Tonga eruption demonstrated the exceptional infrasound detection capabilities of stratospheric balloons, but the advantages for monitoring more common eruptions remain unassessed. This study evaluates the potential of balloon-borne measurements for volcanic monitoring by analysing the entire December 2021 - January 2022 Hunga Tonga eruptive sequence using observations from five Strateole-2 superpressure balloons and the International Monitoring System (IMS) ground-based infrasound network. Balloon records reveal the full chronology of the sequence, showing excellent agreement with satellite and seismic data, and even clarifying ambiguous plume timings. A detailed analysis of the moderate initial eruption on 19 December 2021 demonstrates a key advantage: all in-flight balloons detected a clear and coherent long duration signal, whereas ground-based IMS stations exhibited uneven and noise-limited detection capabilities. While parabolic equation-based infrasound propagations simulations using a volcano-level source reproduce signal celerities reliably, they drastically overestimate the anisotropy in acoustic amplitudes, predicting excessive amplitudes in downwind directions compared to observations. We show that simulating an elevated source within the volcanic umbrella cloud (10-15 km) reduces this anisotropy and yields better agreement with recorded amplitudes, highlighting the importance of the eruption-generated plume as an acoustic source. These findings underscore the added value of balloon-borne sensors for the reliable monitoring of moderate volcanic eruptions, providing insights that are not readily accessible from ground-based networks alone.
- Hardy, P., Podglajen, A., Le Pichon, A., Listowski, C., Hertzog, A., Gullbekk, S. B., Froment, M., Näsholm, S. P., Brissaud, Q., & Schwoebel, L. (2026). Stratospheric balloon observations of infrasound from the 2021-2022 Hunga eruptive sequence and its 19 December 2021 eruption. Journal of Geophysical Research: Atmospheres.