[P-EM13] Coupling Processes in the Atmosphere-Ionosphere System

[PEM13-07] Variations in atmospheric electric field and VLF/LF transmitter signals associated with Tonga volcanic eruption of 15 January, 2022

*Hiroyo Ohya¹, Fuminori Tsuchiya², Jaroslav Chum³, Tatsuya Omori¹, Kazuo Shiokawa⁴ (1.Graduate School of Engineering, Chiba University, 2.Graduate School of Science, Tohoku University, 3.Institute of Atmospheric Physics, Czech Academy of Sciences, 4.Institute for Space-Earth Environmental Research, Nagoya University)

So far, variations in atmospheric electric field (or potential gradient) associated with volcanic lightning discharges, plumes and eruption cloud due to volcanic eruptions have been reported (Firstov et al., 2017). In addition, tropospheric aerosols, which change atmospheric conductivity, are disturbed by volcanic eruptions (Rycroft et al., 2000). However, relationship between atmospheric electric field and neutral atmospheric waves excited by volcanic eruptions is not revealed. On the other hand, several studies for the F-region ionosphere associated with volcano eruptions based on GPS-total electron content (TEC) data have been reported so far (e.g., Heki 2006). These studies reported that acoustic waves excited by volcano eruptions reach up to the F-region ionosphere and caused F-region perturbations. After eruption of the Kelud Volcano, Indonesia, in February 2014, acoustic resonance between the Earth’s surface and lower thermosphere was reported based on TEC data and the seismic wave data (Nakashima et al. 2016). As for D-region ionosphere, there was a report that amplitudes of very low frequency (VLF, 3-30 kHz) transmitter signals were largely depressed and varied with a period of 6-30 minutes during Mt. Kirishima eruptions during 18-27 January, 2011, which suggested that atmospheric gravity waves (AGWs) generated by the eruptions caused the VLF variations (Rozhnoi et al. 2014). In this study, we investigate variations in the atmospheric electric field and VLF/LF transmitter signals associated with Tonga volcanic eruptions of 15 January, 2022 to understand neutral atmospheric waves due to volcanic eruptions. The Hunga Tonga-Hunga Ha‘apai volcano in Tonga (in southern Pacific) explosively erupted during 04:10-04:30 UT on 15 January, 2022, and large pressure variations occurred from the volcano. The atmospheric electric field has been observed in Chiba University (CHB), Japan (35.63N, 140.10E), and Studenec (STU), Czech (50.26N, 12.52E). The distances of CHB and STU from the Tonga volcano were 7789.5 km and 16634.7 km, respectively. The VLF/LF transmitters used in this study were NWC (19.8 kHz, Australia), JJY(40 kHz and 60 kHz, Japan), JJI(22.2 kHz, Japan), BPC(68.5 kHz, China), KRA(24.1 kHz, Korea), and INS(18.2 kHz, India). The receivers were Tainan (TNN, 23.07N, 120.12E) in Taiwan, and Kagoshima (KAG, 31.48N, 130.72E) in Japan. 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 propagation velocity was 310-320 m/s, which is typically horizontal velocity of atmospheric Lamb waves. 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 VLF/LF amplitudes for almost propagation paths showed the similar period of 10-100 minutes around the first arrival time of the Lamb waves. This could be signatures of changes in global electric circuit via Lamb waves excited by Tonga volcanic eruptions. In this presentation, we will report and discuss the phenomena in detail.