[P-EM12] Coupling Processes in the Atmosphere-Ionosphere System

[PEM12-P22] D-Region ionospheric variations induced by a fireball of 23 April 2023, in Hokuriku Japan, using OCTAVE VLF/LF transmitter signals

*古谷 凌汰¹、大矢 浩代¹、土屋 史紀²、中田 裕之¹ (1.千葉大学大学院融合理工学府、2.東北大学大学院理学研究科惑星プラズマ・大気研究センター)

キーワード：VLF/LF帯標準電波、火球、電離圏

Meteors are objects in space that enter the Earth's atmosphere. Meteors brighter than magnitude of -4 are called fireballs. Meteors and fireballs are known to ionize atmospheric neutrals at 80-120 km heights. So far, ionospheric effects on meteors and fireballs have been reported. When a meteoroid was observed in Chelyabinsk, Russia on February 15, 2013, variations in TEC (Total Electron Content) were reported associated with the meteoroids (Perevalova et al., 2015). Furthermore, when a fireball was observed in Hokkaido, Japan, on 18 October 2018, variations in the D-region ionosphere (60-90 km) were reported (Suzuki et al., 2022). These studies indicate that ionospheric variations were caused by acoustic and atmospheric gravity waves generated by fireballs and meteoroids. However, few quantitative studies for the D-region ionosphere associated with meteors and fireballs have been reported. In this study, we investigate variations in the D-region ionosphere during a fireball occurred in Hokuriku region, Japan, at 14:33 UT on 23 April 2023, using VLF (very low frequency, 3-30 kHz) / LF (low frequency, 30-300 kHz) transmitter signals and F-net observed at Kashiwazaki (KZK). The transmitters used in this study were JJY (60 kHz, Saga/Fukuoka, Japan) and BPC (68.5 kHz, China). The receiver was RKB (Rikubetsu, Hokkaido, Japan), one of the OCTAVE networks established by this research group. Variations in the JJY60-RKB amplitudes and phases also showed the same period (300-500 s) based on wavelet analysis. Variations in the BPC-RKB amplitudes and phases showed a period of 300-500 s based on wavelet analysis. The vertical velocity of seismic wave at KZK had a periodic variation of 100-200 s at the arrival time of the acoustic wave excited by the fireball. From these results, we consider that acoustic waves excited by the fireball propagated to the D-region ionosphere and the Earth’s surface, and caused variations in the D-region ionosphere and ground. In this presentation, we will discuss the mechanism of phenomena in detail.