the SC becomes diffusive.

The position of the IPP taken at 14:50 UT was put on dTEC map which is on the right side at the bottom of Figure \[Figure3\] (see purple asterisk). It is clearly seen that the IPP locates near the crest C1. The wavelength of this TID – the distance between the crests C1 and C2 (red arrows) – is approximately 550 km. In the bottom portion of the Figure 3 animation, one can observe the IPP trajectory on dTEC maps from 14:40 UT to 15:50 UT. At 14:40 UT it starts from the position very close to the crest C1, and later reaches the crest C2 at 15:50 UT. On a closer examination, the IPP track is basically along the TID wave front. So the track remains at the valley for a long time. This may explain the long durations of the SCs as well as their uncommon spectral shapes. Evidently, both SCs in the considered case were produced by the same TEC perturbation.

Case $\#$3
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![image](Figure4.png){width="80.00000%"}

Figure \[Figure4\] presents the SCs which are likely caused by the same TID and recorded by different radio telescopes with similar spectral morphology. Panels (a) and (b) of 