the figure represent the CALLISTO GLASGOW and the CALLISTO BIR solar spectrograms, respectively. The dashed horizontal lines on the CALLISTO BIR spectrogram mark the band of the CALLISTO GLASGOW spectrogram in frequency. Three time instants at 09:58 UT (white line), 10:04 UT (purple line), and 10:16 UT (gray line) in both dynamic spectra have been indicated. The IPPs corresponding to the CALLISTO GLASGOW (asterisk) and the CALLISTO BIR (plus) spectrograms for these instants were obtained and plotted on dTEC maps. The corresponding lines and signs have the same colors. Two pairs of SCs in the dynamic spectra of the CALLISTO GLASGOW and BIR stations are denoted as SC-G (I,II) and SC-B (I,II), correspondingly. The animation of this case is available with Figure 4.

The SC-G(I) in panel (a) starts near 09:48 UT at 80.8 MHz. It is a lane drifting from high to low frequencies. During the SC-G(I) life time (09:48 UT-09:58 UT) the successive IPPs lie within the valley between the crests C1 and C2 (red arrows). The IPP taken at 09:58 UT approaches the crest C2 (white asterisk in panel (c)). Because of limited frequency range, some parts of the SC-G(I) are not observable. Nevertheless, one can compare 