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[U09-P11] Effect of the troposheric wind near Japan to the resonance of meteotsunamis by the eruption of Hunga-Tonga Hunga-Ha'apai
Keywords:meteotsunami, pressure wave at sea level, polar front jet, radial velocity, Proudman resonance
Atmospheric waves such as Lambe waves, acoustic waves and gravity waves propagated globally by the eruption of Hunga-Tonga Hunga-Ha'apai on 15 January 2022. Meteotsunamis occurred by pressure disturbances at sea level according to those atmospheric waves, and the oscillation of the sea level higher than several tens of centimeters measured at various coasts: not only Pacific coasts, but Atlantic, Mediterranean, and even the Persian Gulf. In Japan, meteotsunami observed at least 2 hours earlier than that predicted, and several ports measured the maximum wave higher than 1.0m. In the present study, we made data analysis and numerical experiments to focus on the Proudman resonance near Japan, which is one of the important effects of various amplification mechanisms of meteotsunamis.
The propagation velocity of the Lamb wave was calculated using ground pressure observations by Japan Meteorological Agency and Weather News Inc. The pressure wave components were obtained after the band-pass filter with period range of 2-120 minutes. The mean propagation speed was calculated by the distance from the volcano and the elapsed time, which was calculated by the wave setup time at each site and the time of the eruption. The mean propagation speed of Lamb wave estimated with the range of 305-315 m/s, except at Minamitorishima, the nearest station in Japan from the volcano, of 320 m/s. We re-calculate using the time lag from Minamitorishima and other stations in Japan. After the re-calculation, the propagation speed was ranged 280-300 m/s. Himawari-8 image analysis showed the propagation speed of 290-300 m/s, corresponding well to the re-calculated propagation speed. The cause of the deceleration of the ground speed of atmospheric waves near Japan is that the polar front jet stream has moved south to around 30 N in the area around Japan. The negative radial velocity was estimated as 30-50 m/s over the Pacific Ocean around Japan.
We attempted the numerical simulation on the propagation of meteotsunamis, considering the doppler effect by upper winds. We made the normalized pressure wave model from the observation data at Fiji (about 770km from volcano). The run with uniform propagation speed of c0=310 m/s showed that the simulated wave height was as small as 50-60% of the observed wave at NOAA DART stations near Japan. Assuming the deacceleration by upper wind near Japan (6400-8000km from the volcano), the simulated wave height was 1.3-3.0 times higher than that under uniform propagation speed. To discuss the potential of the Proudman resonance, we calculated the Froude number defined as the ratio of the pressure wave speed over the ocean long wave speed. Under the uniform propagation of c=310m/s, the area of 0.8 <Fr< 1.2 was very limited in the ocean trench. Considering the deacceleration, the area of 0.8<Fr<1.2 covered the ocean floor widely in East Japan, and the potential of the Proudman resonance was drastically increased.
Hence, it can be concluded that the wind in the upper troposphere plays an important role in the Proudman resonance of the volcanic meteotsunami. To predict the intensity of the volcanic meteotsunami, the upper wind depend on seasonal or annual cycle should be considered as well as the pressure wave intensity itself and its frequency range.
The propagation velocity of the Lamb wave was calculated using ground pressure observations by Japan Meteorological Agency and Weather News Inc. The pressure wave components were obtained after the band-pass filter with period range of 2-120 minutes. The mean propagation speed was calculated by the distance from the volcano and the elapsed time, which was calculated by the wave setup time at each site and the time of the eruption. The mean propagation speed of Lamb wave estimated with the range of 305-315 m/s, except at Minamitorishima, the nearest station in Japan from the volcano, of 320 m/s. We re-calculate using the time lag from Minamitorishima and other stations in Japan. After the re-calculation, the propagation speed was ranged 280-300 m/s. Himawari-8 image analysis showed the propagation speed of 290-300 m/s, corresponding well to the re-calculated propagation speed. The cause of the deceleration of the ground speed of atmospheric waves near Japan is that the polar front jet stream has moved south to around 30 N in the area around Japan. The negative radial velocity was estimated as 30-50 m/s over the Pacific Ocean around Japan.
We attempted the numerical simulation on the propagation of meteotsunamis, considering the doppler effect by upper winds. We made the normalized pressure wave model from the observation data at Fiji (about 770km from volcano). The run with uniform propagation speed of c0=310 m/s showed that the simulated wave height was as small as 50-60% of the observed wave at NOAA DART stations near Japan. Assuming the deacceleration by upper wind near Japan (6400-8000km from the volcano), the simulated wave height was 1.3-3.0 times higher than that under uniform propagation speed. To discuss the potential of the Proudman resonance, we calculated the Froude number defined as the ratio of the pressure wave speed over the ocean long wave speed. Under the uniform propagation of c=310m/s, the area of 0.8 <Fr< 1.2 was very limited in the ocean trench. Considering the deacceleration, the area of 0.8<Fr<1.2 covered the ocean floor widely in East Japan, and the potential of the Proudman resonance was drastically increased.
Hence, it can be concluded that the wind in the upper troposphere plays an important role in the Proudman resonance of the volcanic meteotsunami. To predict the intensity of the volcanic meteotsunami, the upper wind depend on seasonal or annual cycle should be considered as well as the pressure wave intensity itself and its frequency range.