Revision of Solar Spicule Classification

Solar spicules are the fundamental magnetic structures in the chromosphere and may play a key role in channeling the chromosphere and corona. Recently, it was suggested by De Pontieu et al. that there were two types of spicules with very different dynamic properties, which were detected by the space-time plot technique in the Ca II H line (3968 Å) wavelength from Hinode/Solar Optical Telescope observations. A "Type I" spicule with a 3-7-minute lifetime undergoes a cycle of upward and downward motions; by contrast, a "Type II" spicule fades away within dozens of seconds without a descending phase. We are motivated by the fact that for a spicule with complicated three-dimensional motion the space-time plot, which is made through a slit on a fixed position, could not match the spicule behavior all the time and might lose its real life story. By revisiting the same data sets, we identify and trace 105 and 102 spicules in the quiet Sun (QS) and coronal hole (CH), respectively, and obtain their statistical dynamic properties. First, we have not found a single convincing example of "Type II" spicules. Second, more than 60% of the identified spicules in each region show a complete cycle, i.e., the majority are "Type I" spicules. Third, the lifetimes of the spicules in the QS and CH are 148 s and 112 s, respectively, but there is no fundamental lifetime difference between the spicules in the QS and CH reported earlier. Therefore, the suggestion of coronal heating by "Type II" spicules should be taken with caution.