Type II solar radio bursts are the result of energetic electrons accelerated by a shock. This kind of burst appears on dynamic spectra as lanes drifting slowly from higher to lower frequencies. Often, scientists observe a fundamental harmonic structure, which sometimes exhibits a division on each band called band split.
source https://www.lifetechnology.com/blogs/life-technology-news-blog/detection-of-spike-like-structures-near-the-front-of-a-shock-driven-solar-radio-burst