valley of the moving wave-like structure. The SC could still exist below 35 MHz with a longer duration. In this case, even assuming the duration of the SCs is twice longer than at 35 MHz, the thus-obtained IPPs would still remain being in the valley. This SC can be regarded as a classical manifestation of the focusing of solar radiation caused by MSTIDs.

Case $\#$2
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Unlike the previous case, the one in the bottom part of Figure \[Figure3\] is characterized by non-classified spectral structures. Besides, the total duration of the event is more than 1 h, that makes it rare too. Seemingly, there are two long-living SCs overlapping in time. The first SC starts at 14:40 UT in time and at 45 MHz in frequency. It takes a tunnel-like form, which firstly goes down in frequency to 35 MHz and then keeps a slight slope from 15:00 UT up to the end at 15:40 UT. The second SC has a curved backbone-like structure with a number of filaments extended out from it. Tentatively, this SC may be attributed to a combination of the fiber-like and the fringe-like types. The SC’s filaments firstly appear near 15:18 UT. From 15:40 UT 