on the time spans of the corresponding dynamic spectra shown in Figure \[Figure2\](a-h). There are nearly 50 SCs in Figure \[Figure2\]. Below we will consider several cases to demonstrate the method of our study.

![image](Figure2.png){width="100.00000%"}

Case $\#$1
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![image](Figure3.png){width="80.00000%"}

In the upper part of Figure \[Figure3\] the SC recorded by the CALLISTO ESSEN is presented. This SC is almost symmetrical and likely belongs to the X-like type. It consists of two bright envelopes, crossing in frequency near 50 MHz, and its upper part is diffusive. The position of the IPP at 09:44:00 UT (near the SC’s symmetry line) was determined and plotted on the dTEC map. It is seen that the IPP (white asterisk) locates in the center of the valley between two crests C1 and C2 as pointed by red arrows.

The upper part of Figure \[Figure3\] represents a still frame of the top part of the animation, which shows the obtained IPP positions imposed on dTEC maps from 09:39:00 UT to 09:46:30 UT with a 30-sec cadence. This time range corresponds to the longest SC duration at the lowest frequency ($\sim35$ MHz) in the spectrogram. It can be seen that during this time all IPPs lie within the 