Interplay of three kinds of motion in the disk counterpart of type II spicules: up-flow, transversal and torsional motions

TL;DR

This study investigates the complex motions of solar spicules, identifying signatures of up-flow, swaying, and torsional motions through high-resolution observations, revealing their coexistence and contribution to observed Doppler shifts.

Contribution

It provides new observational evidence of red-shifted excursions (RREs) alongside blue-shifted RBEs, demonstrating the simultaneous presence of multiple motion types in spicules.

Findings

RREs are similar to RBEs in properties and are found across the solar disk.

The imbalance of RBEs and RREs suggests up-flows significantly influence Doppler shifts.

Parallel RRE/RBE pairs indicate torsional motions are common in spicules.

Abstract

Recently, it was shown that the complex dynamical behaviour of spicules has to be interpreted as the result of simultaneous action of three kinds of motion: (1) field aligned flows, (2) swaying motions, and (3) torsional motions. We use high-quality observations from CRISP at the SST to investigate signs of these different kinetic modes in spicules on the disk. Earlier, rapid blue-shifted excursions (RBEs), short-lived absorption features in the blue wing of chromospheric spectral lines, were identified as the disk counterpart of type II spicules. Here we report the existence of similar absorption features in the red wing of the Ca II 8542 and Halpha lines: rapid red-shifted excursions (RREs). RREs are found over the whole solar disk and are located in the same regions as RBEs: in the vicinity of magnetic field concentrations. RREs have similar characteristics as RBEs: they have similar lengths, widths, lifetimes, and average Doppler velocity. The striking similarity of RREs to RBEs implies that RREs are a manifestation of the same physical phenomenon and that spicules harbour motions that can result in a net red-shift when observed on-disk. We find that RREs are less abundant than RBEs and we interpret the higher number of RBEs and the decreased imbalance towards the limb as an indication that field-aligned up-flows have a significant contribution to the net Dopplershift. Most RREs and RBEs are observed in isolation but we find many examples of parallel and touching RRE/RBE pairs which appear to be part of the same spicule. We interpret the existence of these RRE/RBE pairs as signs that torsional motion is an important characteristic of spicules. The fact that most RBEs and RREs are observed in isolation agrees with the idea that transversal swaying motion is another important kinetic mode. We find examples of transitions from RRE to RBE and vice versa.