1:45 PM - 3:15 PM
[MIS23-P09] Internal gravity waves observed in Japan after Tonga volcanic eruption in January 2022
Keywords:Volcanic eruption, Internal gravity wave, Himawari-8, Volcanic meteotsunami, Helmholtz frequency
Atmospheric waves such as Lamb wave, and Pekeris wave generated by the volcanic eruption of Hunga Tonga-Hunga-Ha'api on 15 January 2022. The propagation of those atmospheric waves resulted in generation of the volcanic meteotsunamis obeserved globally. Indeed the mangitude of the pressure disturbance at sea level was 0.3-5.0 hPa, but the maximum wave height was as high as several tens of centimeters and some coasts exceeded to 1.0 meter. In Japan, the maximum wave was observed between 23:00 on January 15 and 3:00 on January 16 JST, more than 2 hours later from the first waves due to passing of Lamb waves. In the same time, ground-based observation by Japan Meteorological Agency detected the pressure waves with the amplitude as small as 0.1~0.3 hPa. In this study, we attempted to detect the atmospheric waves from Himawari-8 infrared images provided by NICT, Japan. We used 10 channles of the gridded data from Band-07 to Band-16 with horizontal resolution of 0.02 degree and scan interval of every 2.5 minutes. We computed the second-order time derivative of brightness temperature (Tb2d) for each channel according to Otsuka (2022). Two dimensional band-pass filter ranged between 0.3 and 2.5 arc-degrees were applied to detect the targaed wave components.
After the analysis, we detected the Tb2d waves in Japan region with the amplitude of 5-10 μKs-2 as Lamb waves after 6-8 hours from the eruption. Those waves was detected by all channels of Band-07 to Band-16. Secondary Tb2d waves were also detected in Japan area after 9-12 hours from the eruption, but only seen in Band-08 and Band-12. Since Band-12 has high response both in lower troposphere and around the tropopause, we calculated differece Band-12 from Band-13. As the result, the wave pattern could be seen more clearly. We analysed the phase speed of secondary waves as 190-210 m/s relative to ground with the period of 600-900 seconds. The propagation direction oriented 10-15 degree clockwise from the azimuth from the Tonga volcano. Considering doppler effects of upper winds, the phase speed of the secondary wave estimated as 240-250 m/s with the derection nearly as the azimuth from the volcano. After the caluculation the veritical profile of the squared Helmholz frequency n2 using upper air observation by GPS-sondes by JMA, the layers of internal gravity mode were found in 100-200 hPa levels and in 300-400 hPa levels, corrsponding with the targeted layer of Band-12 and Band-08 respectively. The pressure flucutuation estimated as 0.5-0.7 hPa from Tb2d waves, which was several times greater than that of ground level observation.
The internal gravity waves detected in this study seemed to play an important role in amplifying volcanic meteotsunamis in the Pacific coasts of Japan with the proundman resonance and eigenoscillation.
After the analysis, we detected the Tb2d waves in Japan region with the amplitude of 5-10 μKs-2 as Lamb waves after 6-8 hours from the eruption. Those waves was detected by all channels of Band-07 to Band-16. Secondary Tb2d waves were also detected in Japan area after 9-12 hours from the eruption, but only seen in Band-08 and Band-12. Since Band-12 has high response both in lower troposphere and around the tropopause, we calculated differece Band-12 from Band-13. As the result, the wave pattern could be seen more clearly. We analysed the phase speed of secondary waves as 190-210 m/s relative to ground with the period of 600-900 seconds. The propagation direction oriented 10-15 degree clockwise from the azimuth from the Tonga volcano. Considering doppler effects of upper winds, the phase speed of the secondary wave estimated as 240-250 m/s with the derection nearly as the azimuth from the volcano. After the caluculation the veritical profile of the squared Helmholz frequency n2 using upper air observation by GPS-sondes by JMA, the layers of internal gravity mode were found in 100-200 hPa levels and in 300-400 hPa levels, corrsponding with the targeted layer of Band-12 and Band-08 respectively. The pressure flucutuation estimated as 0.5-0.7 hPa from Tb2d waves, which was several times greater than that of ground level observation.
The internal gravity waves detected in this study seemed to play an important role in amplifying volcanic meteotsunamis in the Pacific coasts of Japan with the proundman resonance and eigenoscillation.