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[HDS06-P13] One- dimensional calculation of sea level changes caused by atmospheric pressure waves.
Keywords:atmospheric Lamb waves, Tonga
The volcano of Hunga Tonga-Hunga Ha'apai off the Tonga Islands erupted around 13:10 JST on January 15, 2022. It is away about 8,000 km from Japan. The tsunamis related to the eruption were observed throughout the Pacific Ocean, including Japan, but tsunami arrival time in Japan was noticeably earlier than regular tsunamis. The tsunami was small in Nauru, about 3,000 km from the source. However, more than one-meter tsunamis were observed along the Pacific Rim. Air-pressure fluctuations called atmospheric Lamb waves may have caused the tsunamis because they arrived simultaneously.
This study conducted one-dimensional calculations of meteorological tsunamis using a coupled atmosphere-ocean model that includes the atmospheric pressure term as an external force in the linear long wave equation. We used a finite difference scheme to solve the equations. In the numerical simulations, a traveling sine wave expressed the air-pressure wave. Based on the observed data, the speed and amplitude of the pressure wave were assumed to be 300 m/s and 2 hPa, respectively.
We investigated the deformation of the generated meteorological tsunamis by changing the shape of the seafloor from "flat," "constant slope," to "real bathymetry". The horizontal distance in the calculation model was 8,000 km, almost the same as the distance between Japan and Tonga. For calculations for flat seafloor topography, water depth changed from 1,000 m to 9,000m. The maximum tsunami height of the generated meteorological tsunamis was less than 0.02m for water depths from 1,000m to 5,000m. the tsunami height gradually increased with water depths from 5000m to 9000m. The maximum wave height appeared to be 0.75 m at a depth of 9,000 m due to the pronounced Proudman resonance effect. We defined two slopes for calculations of constant slope bathymetry. One was an upslope with a slope of 10 degrees and a maximum water depth of 10,000 m; the other was a downslope with a slope of 10 degrees and a maximum water depth of 11,000 m. The air-pressure wave excited a forced wave on the upslope, but as the water depth became shallow, the forced tsunami wave could not keep up with the speed of the Lamb wave to be a free wave. The air-pressure wave created a new forced wave. On the other hand, the forced waves excited by the downslope increased with depth.
In a one-dimensional analysis using bathymetry between Japan and Tonga, a complex sea level change was excited by the repetitive generation of forced waves due to the complex seafloor topography. Unlike the usual seismic tsunami excitation, the pressure wave continues to excite new tsunamis in the entire computational domain as it propagates. The duration of the 2022 Tongan tsunami was very long, which may be related to the uncommon tsunami excitation by the air-pressure wave. However, for accurate tsunami predictions, it is necessary to perform two-dimensional calculations instead of one-dimensional calculations. We will address it in the subsequent analysis.
This study conducted one-dimensional calculations of meteorological tsunamis using a coupled atmosphere-ocean model that includes the atmospheric pressure term as an external force in the linear long wave equation. We used a finite difference scheme to solve the equations. In the numerical simulations, a traveling sine wave expressed the air-pressure wave. Based on the observed data, the speed and amplitude of the pressure wave were assumed to be 300 m/s and 2 hPa, respectively.
We investigated the deformation of the generated meteorological tsunamis by changing the shape of the seafloor from "flat," "constant slope," to "real bathymetry". The horizontal distance in the calculation model was 8,000 km, almost the same as the distance between Japan and Tonga. For calculations for flat seafloor topography, water depth changed from 1,000 m to 9,000m. The maximum tsunami height of the generated meteorological tsunamis was less than 0.02m for water depths from 1,000m to 5,000m. the tsunami height gradually increased with water depths from 5000m to 9000m. The maximum wave height appeared to be 0.75 m at a depth of 9,000 m due to the pronounced Proudman resonance effect. We defined two slopes for calculations of constant slope bathymetry. One was an upslope with a slope of 10 degrees and a maximum water depth of 10,000 m; the other was a downslope with a slope of 10 degrees and a maximum water depth of 11,000 m. The air-pressure wave excited a forced wave on the upslope, but as the water depth became shallow, the forced tsunami wave could not keep up with the speed of the Lamb wave to be a free wave. The air-pressure wave created a new forced wave. On the other hand, the forced waves excited by the downslope increased with depth.
In a one-dimensional analysis using bathymetry between Japan and Tonga, a complex sea level change was excited by the repetitive generation of forced waves due to the complex seafloor topography. Unlike the usual seismic tsunami excitation, the pressure wave continues to excite new tsunamis in the entire computational domain as it propagates. The duration of the 2022 Tongan tsunami was very long, which may be related to the uncommon tsunami excitation by the air-pressure wave. However, for accurate tsunami predictions, it is necessary to perform two-dimensional calculations instead of one-dimensional calculations. We will address it in the subsequent analysis.