Abstract
Typhoon Faxai was a very powerful typhoon that made landfall and passed through Japan on September 8-9, 2019. In the previous study that used Total Electron Content (TEC) acquired by the GNSS navigation system,
Concentric Traveling Ionospheric Disturbances (CTIDs) were observed within 250 km of Faxai. In this study, to investigate ionospheric disturbances at lower altitudes than cannot be observed using TEC, we examined the
ionospheric disturbances associated with Faxai using a High-Frequency Doppler (HFD) sounding system. It was found that disturbances corresponding to the CTIDs were observed by HFD sounding. The horizontal velocity of these disturbances was estimated at about 200 m/s, which is consistent with the horizontal velocities reported by the previous study. The period of the disturbances suggests that the ionospheric disturbances corresponding to the CTIDs is caused by the Internal Gravity Waves (IGWs). Since the gravity wave can propagate from the ground to the upper atmosphere, the CTIDs associated with Faxai distributed at all altitudes with the same velocity in the entire F-region. HFD observation also revealed that the typhoon generated acoustic waves, which caused short period disturbances.
