in panel (c)), the SC-B(I) appears.

Figure \[Figure4\](d) demonstrates the IPP positions at 10:04 UT. The IPP associated with the CALLISTO BIR antenna is in the valley (purple plus), while the IPP associated with the CALLISTO GLASGOW antenna is on the crest C2 (purple asterisk). On the dTEC map the crest C2 is partly depressed within $-6^\circ$–$5^\circ$ range of longitudes. Its short fragment is observable from $-8^\circ$ to $-6^\circ$ in longitude. Thus, two valleys in between the crests C1, C2 and C3 can be seen along latitude and in the longitude belt from $5^\circ$ to $11^\circ$. However, there is only one comparably wider valley between the crests C1 and C3 within $-6^\circ$–$5^\circ$ range of longitudes. The IPP track of the CALLISTO GLASGOW antenna crosses two valleys. As a result, the SC-G(I) and SC-G(II) occur with difference in time. The IPP track of the CALLISTO BIR antenna moves across one valley. Interestingly, two SCs – the SC-B(I) and SC-B(II) – emerge as well but overlap in time. We have already described similar occurrence in the previous case in the NDA dynamic spectrum. The possible interpretation will be given in section \[Sect:Summary and Discussion\].

In Figure \[Figure4\](e) the IPP locations at 10:16 