Rapid Evolution of Type II Spicules Observed in Goode Solar Telescope On-disk H α Images

We analyze ground-based chromospheric data acquired at a high temporal cadence of 2 s in wings of the Hα spectral line using the Goode Solar Telescope operating at the Big Bear Solar Observatory. We inspected a 30 minute long Hα−0.08 nm data set to find that rapid blueshifted Hα excursions (RBEs), which are a cool component of type II spicules, experience very rapid morphological changes on timescales of the order of 1 s. Unlike typical reconnection jets, RBEs very frequently appear in situ without any clear evidence of Hα material being injected from below. Their evolution includes inverted "Y," "V," "N," and parallel splitting (doubling) patterns as well as sudden formation of a diffuse region followed by branching. We also find that the same feature may undergo several splitting episodes within about a 1 minute time interval.