Fig. 5

a High-pass filtered slant TEC time series at three stations observed using J07, the QZSS geostationary satellite, at three GNSS stations 0603, 2007, and P217 (Fig. 1b). Frequency components of the 4-h data 5:20–9:20 UT (shown with a dashed line) obtained using the Blackman–Tukey method are shown in (b). We see three strong peaks (3.7, 4.4, and 5.4 mHz) and one weaker peak (4.8 mHz) for the TEC data at all the three stations (colors correspond to those in (a)