Traveling Ionospheric Disturbances of the 11 March 2011 M9.0 Tohoku Earthquake, the 31 March 2013 Stationary Front, the 10-14 September 2021 Typhoon Chanthu Observed by HF Doppler Sounding Systems in Taiwan

Ionospheric Doppler frequency fluctuations triggered by the 11 March 2011 M9.0 Tohoku earthquake, the 31 March 2013 stationary front, and the 10-14 September 2021 Typhoon Chanthu have been observed by using HF (high frequency) Doppler sounding systems in Taiwan. Hilbert-Huang Transform (HHT) and Fourier Transform (FT) analyses are applied to find characteristic periods of the Doppler frequency shifts of the three events. Results show that upon seismic waves of the 2011 Tohoku earthquake arriving in Taiwan at 14:10 LT (local time), noticeable periods of 5-20 and 180-270 seconds of Doppler frequency shifts are observed; while the stationary front impending Taiwan on 31 March 2013, obvious Doppler frequency shift oscillations in periods of 30 minutes are detected; and when typhoon Chanthu approached Taiwan at 06:00-08:00 LT on 11 September 2021, the ionospheric Doppler frequency shift fluctuates with a prominent 13-minute period. These results show that seismic waves in the lithosphere and acoustic/gravity waves in the atmosphere can significantly induce traveling atmospheric disturbances near the Earth’s surface, which further travel into the upper atmosphere, and activate traveling ionospheric disturbances within.