A TGF from the 2022 Hunga Tonga-Hunga Ha'apai Volcanic Eruption

The Hunga Tonga-Hunga Ha'apai submarine volcano resumed activity in late 2021 and early 2022. Violent eruptions on 2022 January 14th and 15th launched a tall ash plume with high water content that produced extremely high lightning rates. We report a terrestrial gamma-ray flash (TGF) that was produced by the volcanic lightning and observed from space by the Fermi Gamma-ray Burst Monitor (GBM). Observations by radio lightning networks and especially by the Geostationary Lightning Mapper show that the only lightning close enough to produce a TGF detectable by Fermi GBM was from the volcano's plume. With the observing duration of Fermi, observing a single TGF is consistent with the hypothesis that the volcanic lightning of this eruption produced TGFs at the average rate of thunderstorm lightning. The observation of a strong TGF from space also indicates that the electric field was oriented so as to accelerate electrons upward.