2024 年 12 巻 1 号 論文ID: 22-00314
Meteotsunamis by atmospheric pressure disturbances following the 2022 Tonga volcanic eruption were investigated based on theoretical analysis and observation. The atmospheric pressure with an amplitude of approximately 2 hPa and sea surface elevations greater than 1 m were observed around Japan. For a uniformly sloping bottom, analytical solutions of sea level change due to atmospheric pressure disturbance were derived. They include the forced wave and two free-wave components propagating in opposite directions, which are described in terms of the Hankel functions of the first and second kinds of order zero. The approximated solution for the forced wave was obtained by neglecting the terms of order of the bottom slopes, which was similar to Proudman’s forcing-wave component. The envelope functions of tsunami waves were estimated by using the Hilbert transform of tsunami waveforms and the arrival times of amplified waves and their average propagation speeds were also estimated. As a result, the average propagation speeds were about 170–220 m/s, which approximately coincides with the speed of the gravity waves in the Pacific Ocean. The amplitudes of amplified waves, energies, and energy fluxes of sea level fluctuations showed that they mostly increased with the great-circle distance from Tonga to the stations, which implied that energy was transported from the air to tsunamis. Lamb wave, acoustic wave, and atmospheric gravity wave components were decomposed by using the time series model with the trend, autoregressive, and noise components. The atmospheric gravity waves were extracted from the autoregressive component, and their celerity was estimated to be about 200 m/s at 15:00 (UTC). Tsunami waves in the ocean were found to be amplified up to several tens of times due to the Proudman resonance with the atmospheric gravity waves when the resonance time becomes 1–2 h.
