9:15 AM - 9:30 AM
[PEM12-02] Coupling between the D-region ionosphere and atmosphere due to Lamb and Pekeris waves associated with the 2022 Tonga volcanic eruption based on observations of AVON VLF/LF transmitter signals
★Invited Papers
The Hunga Tonga-Hunga Ha‘apai volcano in Tonga (in southern Pacific, 20.54S, 175.38W) explosively erupted around 04:10 UT on 15 January, 2022, and large pressure variations occurred from the volcano. Large and medium scale traveling ionospheric disturbances (LSTID and MSTID) due the eruptions were observed (Themens, 2022), which were caused by Lamb wave excited by the eruptions. Due to magnetic conjugate effect, the northern hemisphere TIDs appear three hours prior to the arrival of the Lamb wave (Lin et al., 2022). Both direct and conjugate TIDs match with the theoretical dispersion relation of the atmospheric Lamb and gravity modes. In addition to the Lamb wave, Pekeris waves occurred by the eruption (Watanabe et al., 2022). The Lamb waves are a kind of acoustic one, and propagate horizontally with phase velocity of ~310 m/s. On the other hand, Pekeris waves are internal resonance mode that propagate horizontally with phase velocity of ~240 m/s. The Pekeris waves have anti-phase between the mesosphere and the stratosphere, while the Lamb waves are in-phase vertically. The energy of the Pekeris waves is closed between stratopause and mesopause, so amplitude of Pekeris waves becomes large in the upper stratopause (about 45-85 km height). However, variations in the D-region ionosphere due to the Lamb and Pekeris waves associated with the eruptions has not been revealed at all. In this study, we investigate variations in VLF/LF transmitter signals and atmospheric electric field (or potential gradient) to understand coupling between the D-region ionosphere and atmosphere associated with Tonga volcanic eruptions of 15 January, 2022. The VLF/LF transmitters used in this study were JJY(60 kHz, Japan), JJI(22.2 kHz, Japan), and BPC(68.5 kHz, China). The receivers were Tainan (TNN, 23.07N, 120.12E) in Taiwan, where is one of Asia VLF observation network (AVON). We used 0.1-s sampling amplitude data. Unfortunately, there were no phase data for all paths on that day. The minimum distances of the JJI-TNN, JJY60kHz-TNN, and BPC-TNN propagation paths from the Tonga volcano were 8167.7 km, 8311.6 km, and 8499.9 km, respectively. The atmospheric electric field has been observed in Chiba University (CHB), (35.63N, 140.10E), Seikei High School (SHS, Tokyo, 35.72N, 139.57E), Japan, and Studenec (STU), Czech Republic (50.26N, 12.52E). The distances of CHB, SHS, and STU from the Tonga volcano were 7789.5 km, 7830.4 km, and 16634.7 km, respectively. The first variations in pressure data were seen around 10:57 UT and 19:03 UT on 15 January in CHB and STU, respectively. The VLF/LF amplitudes for all three paths showed variations with a period of <10 minutes at arrival times of the Lamb and Pekeris waves. The phase velocity of the Lamb and Pekeris waves were ~307 m/s and ~235 m/s, respectively, which was similar phase velocities with previous studies (Watanabe et al., 2022). On the other hand, after arrival time of the Lamb wave, the atmospheric electric field at CHB showed similar variations with the pressure data at CHB. The periods of the variations were 40-50 and 80-100 minutes. The amplitude of the variation in the atmospheric electric field at CHB and STU was similar after arrival time of the Lamb wave at each site. There were variations in atmospheric electric field with a period of 10-100 minutes at CHB at the first (direct) and second (rounding the Earth) arrival times of the Lamb waves. The conductivity in the atmosphere might change due to Lamb wave excited from the Tonga volcanic eruptions. In this presentation, we will discuss the mechanism of the phenomena in detail.