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

We analyze ground-based chromospheric data acquired at a high temporal cadence of 2 s in wings of the H_α spectral line using the Goode Solar Telescope operating at the Big Bear Solar Observatory. We inspected a 30 minute long H_α-0.08 nm data set to find that rapid blueshifted H_α 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 H_α 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.