Fig. 4From: Medium-scale traveling ionospheric disturbances over Taiwan observed with HF Doppler sounding(Left) an example of a Doppler shift spectrogram analyzed for one 90-min interval analyzed during Super Typhoon Meranti starting on September 13, 2016, at 9:00 UT. (Right) a normalized energy map calculated using the slowness method from the Doppler shift time series obtained for the observations shown on the leftBack to article page