Characteristics of Tsunamis Observed in Japan due to the Air Wave from the 2022 Tonga Eruption

Abstract A large eruption of the Hunga Tonga-Hunga Haʻapai volcano in Tonga on January 15, 2022 generated air-sea coupled tsunamis observed at the ocean-bottom pressure sensor network along the Japan Trench (S-net) in Japan. Initial tsunamis from the 2022 Tonga eruption, detected by 106 ocean bottom pressure sensors, were well modeled by an air-sea coupled tsunami simulation, with a simple atmospheric pressure pulse having a half-wavelength of 300 km and a peak amplitude of 2 hPa. A one-dimensional air-sea coupled tsunami simulation having a simple bathymetry shows that an input atmospheric pressure pulse with a short half-wavelength of 50 km, which is shorter than the length of the slopes, caused an amplitude increase via the Proudman resonance effect near the deep trench. The wavefront distortion due to the separation of the air-sea coupled wave (v=312 m/s) and sea wave (v= sqrt(gd)) is also significant near the shore. In contrast, these effects are not significant for the half-wavelength of the input atmospheric pressure pulse of 300 km. These results indicate that observing the wavelength of an atmospheric pressure pulse due to an eruption is important for forecasting the heights of air-sea coupled tsunamis.