Revision of Solar Spicule Classification

TL;DR

This study revisits solar spicule classification, analyzing their dynamic properties and challenging the existence of 'Type II' spicules, suggesting most are 'Type I' with similar lifetimes in different solar regions.

Contribution

The paper provides a comprehensive reanalysis of spicule data, questioning the previous classification and offering new statistical insights into their lifetimes and behaviors.

Findings

No convincing 'Type II' spicules found in the data.

Over 60% of spicules show a complete cycle, indicating they are mostly 'Type I'.

Spicule lifetimes are approximately 148s in QS and 112s in CH, with no fundamental difference.

Abstract

Solar spicules are the fundamental magnetic structures in the chromosphere and considered to play a key role in channelling 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 space- time plot technique in the Ca ii H line (3968 A) wavelength from Hinode/SOT observations. 'Type I' spicule, with a 3-7 minute lifetime, undergoes a cycle of upward and downward motion; in contrast, 'Type II' spicule fades away within dozens of seconds, without descending phase. We are motivated by the fact that for a spicule with complicated 3D 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 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. Secondly, more than 60% of the identified spicules in each region show a complete cycle, i.e., majority spicules are 'Type I'. Thirdly, the lifetime of spicules in QS and CH are 148 s and 112 s, respectively, but there is no fundamental lifetime difference between the spicules in QS and CH reported earlier. Therefore, the suggestion of coronal heating by 'Type II' spicules should be taken with cautions. Subject headings: Sun: chromosphere Sun:transition region Sun:corona