the events would present exact morphologies and occurrence times regardless of the location of radio observatories. In this work, we have demonstrated a collection of meter-decameter solar dynamic spectra obtained by various radio instruments around Europe. It is seen that SCs occur almost uniquely in each dynamic spectrum. Thus, the peculiar features of SCs are not of solar origin, but resulted from the varying ionosphere irregularities through which the solar radiation propagates.

The above-mentioned statement is further supported by the observations of SCs in cases $\#$3 and $\#$4. In case $\#$3, two pairs of very similar SCs were recorded. We found that the focusing was initiated by the same TEC perturbation. However, existing variations of parameters within it brought distinctions in the respective SCs. In case $\#$4, we established that because of the vicinity of radio observatories, both antennas received the solar radiation which passed through the same region of the TID valley. So, identical SCs were detected.

It is necessary to clarify the appearances of overlapping SCs, which are caused by single TID valleys like in cases $\#$2 and $\#$3. It is expected that one TID valley may cause one caustic surface in space which is registered as a 