[M-IS24] 大気電気学：大気電気学分野での高エネルギー現象

[MIS24-04] Observation of Gravity Waves Propagation in The Lower Ionosphere during 2019 Typhoon 15 using Two Parallel Ionospheric Perturbation Models Based on the 2D FDTD Method

*Antrisha Daneraici Setiawan¹、Hiroshi Kikuchi²、Yasuhide Hobara^1,2 (1.Graduate School of Informatics and Engineering, School of Informatics and Engineering, The University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan、2.Center for Space Science and Radio Engineering, The University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan)

キーワード：Atmospheric Gravity Waves, FDTD, Ionospheric Perturbation, VLF Networks

We observed the ionospheric perturbation using the VLF transmitter signal receiving network during 2019 Typhoon 15. The VLF transmitter/receiver NPM-MSR (Hawaii to Moshiri) and NPM-YMG (Hawaii to Yamaguchi) form a parallel path relative to the path of Typhoon 15 over the North Pacific Ocean. This configuration makes it possible to observe the Atmospheric Gravity Waves (AGWs) propagation in two separate VLF paths by using the ionospheric perturbation model. The wavelet spectrogram of the observed VLF signals shows high intensity with an oscillation period of 60–80 minutes on 4 Sep. 2019 and of 100-120 minutes on 5 Sep. 2019. Those spectra occurred following the peak of cloud height of the typhoon while the high fluctuation of VLF signals is mostly caused by lightning activity, especially in the Fresnel zone near the receiver. The ionospheric perturbation height variation of the lower ionosphere is modeled by 2D FDTD (Two-Dimensional Finite-difference time-domain method) based on the observed VLF signals of 30-minute time intervals. It shows a similar fluctuation pattern at NPM-YMG and NPM-MSR paths with a time delay of 2.5 and 2 hours on 4 Sep. and 5 Sep. 2019 respectively. The perturbation height variation defines the amplitude of AGWs with a peak of 88 km and a minimum of 83 km. The delay shows the phase velocity of AGWs are 94.2 m/s and 117.8 m/s on 4 Sep. and 5 Sep. 2019 respectively. The AGWs propagate faster on 5 Sep. 2019 due to a lower frequency spectrum than on 4 Sep. 2019.