Interplay of Three Kinds of Motion in the Disk Counterpart of Type Ii Spicules: Upflow, Transversal, and Torsional Motions

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 the CRisp Imaging SpectroPolarimeter at the Swedish 1-meter Solar Telescope 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 Hα 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: the RRE/RBE detection count ratio is about 0.52 at disk center and 0.74 near the limb. 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 of the structure. 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 and the observation that many RREs and RBEs have varying Dopplershift along their width 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. These transitions sometimes appear to propagate along the structure with speeds between 18 and 108 km s −1 and can be interpreted as the sign of a transverse (Alfvénic) wave.

Chromospheric Rapid Blueshifted Excursions Observed With Ibis and Their Association With Photospheric Magnetic Field Evolution

“…The RBEs are seen to be located mainly around the boundary of the supergranular cells (depicted by the dashed lines in Figure 1(b)) with some residing inside the cells, as also observed by Lee et al (2000). Based on a visual inspection, the shape of these disk-center quiet-Sun RBEs is mostly round or elongated, similar to the result of Langangen et al (2008) studies, the target region, either in the quiet-Sun or coronal holes, had obvious magnetic concentrations; accordingly, RBEs were mainly elongated and found in the inner edge of the conspicuous chromospheric rosette structures (Langangen et al 2008;Rouppe van der Voort et al 2009;Sekse et al 2012Sekse et al , 2013aSekse et al , 2013b. In contrast, we are looking at a very quiet region as shown by the highly sensitive Hinode LOS magnetogram; no well-formed fibril or rosette structure is discernible in the Ca ii 8542 line center image (Figure 1(a)).…”

THE APPEARANCE OF SPICULES IN HIGH RESOLUTION OBSERVATIONS OF Ca ii H AND Hα

“…But spicules have clear spectral signatures in the form of Doppler-shifted, wider line profiles with increased absorption in the red or blue wings. Such signatures have been observed for spicules on disk (e.g., Langangen et al 2008;Rouppe van der Voort et al 2009;Sekse et al 2013b;Yurchyshyn et al 2013;Kuridze et al 2015) and off limb (Pereira et al 2014).…”

“…Spicules stand out in such Dopplergrams, which eliminate most of the photospheric background and show in great spatial detail their predominant line of sight motions. The abundances of spicules at different Dopplergrams reflect their velocity distribution (of the three kinds of motions: upflow, transverse, and torsional; see Sekse et al 2013b). In the far wing images one sees a lot less events, presumably the extreme tail of the motion distribution.…”

“…The large spatial superposition of spicules, particularly at the limb, makes it challenging to track every individual spicule (e.g., see "Selection Effects and Errors" in Pereira et al 2012). Spicules also recur frequently from the same footpoint region (Beckers 1968;Suematsu et al 1995;De Pontieu et al 2011;Pereira et al 2012;Sekse et al 2013b;Yurchyshyn et al 2013), meaning that when a particular spicule disappears it can be quickly replaced by another of similar intensity in the same place. Judge et al (2012;hereafter JCR12) study disk spicules at a wavelength of Hα + 0.11 nm, and find spicules that appear and disappear suddenly over several Mm.…”

CRISPRED: A data pipeline for the CRISP imaging spectropolarimeter

“…These heterogeneous pieces of code have since been incorporated into an object-oriented IDL structure with computationally demanding parts performed in C subprograms called as dynamically loadable modules (DLMs). Early versions of CRISPRED have been used by several authors to reduce and prepare their data, given that a basic framework has been functional since 2011 (e.g., Watanabe et al 2012;Scharmer et al 2013;de la Cruz Rodríguez et al 2013;Vissers et al 2013;Sekse et al 2013;Wedemeyer et al 2013; Rouppe van der Voort & de la Cruz Rodríguez 2013; Leenaarts et al 2014).…”