Abstract
Abstract We investigate high-resolution spectroscopic and imaging observations from the CRisp Imaging SpectroPolarimeter (CRISP) instrument to study the dynamics of chromospheric spicule-type events. It is widely accepted that chromospheric fine structures are waveguides for several types of magnetohydrodynamic (MHD) oscillations, which can transport energy from the lower to upper layers of the Sun. We provide a statistical study of 30 high-frequency waves associated with spicule-type events. These high-frequency oscillations have two components of transverse motions: the plane-of-sky (POS) motion and the line-of-sight (LOS) motion. We focus on single isolated spicules and track the POS using time–distance analysis and in the LOS direction using Doppler information. We use moment analysis to find the relation between the two motions. The composition of these two motions suggests that the wave has a helical structure. The oscillations do not have phase differences between points along the structure. This may be the result of the oscillation being a standing mode, or that propagation is mostly in the perpendicular direction. There is evidence of fast magnetoacoustic wave fronts propagating across these structures. To conclude, we hypothesize that the compression and rarefaction of passing magnetoacoustic waves may influence the appearance of spicule-type events, not only by contributing to moving them in and out of the wing of the spectral line but also through the creation of density enhancements and an increase in opacity in the Hα line.
Highlights
Solar spicules are dynamic jet-like structures observed at chromospheric temperatures that typically live for a few minutes and reach heights of 3000–4000 km in the solar atmosphere (Thomas 1948; Beckers 1968, 1972; Sterling 1998, and references therein)
High-cadence data have revealed a new type of spicule-type event that suddenly appears in the field of view (FOV) of the narrowband filter without any evidence of evolution (Judge et al 2011, 2012; Lipartito et al 2014; Shetye et al 2016b; Pereira et al 2016)
We identify the dominant periodicities in the two time series t1 and t2 using the continuous wavelet transform (CWT; Torrence & Compo 1998) using a Morlet mother wavelet
Summary
Solar spicules are dynamic jet-like structures observed at chromospheric temperatures that typically live for a few minutes and reach heights of 3000–4000 km in the solar atmosphere (Thomas 1948; Beckers 1968, 1972; Sterling 1998, and references therein). Advances in ground-based instrumentation, such as CRisp Imaging SpectroPolarimeter (CRISP; Scharmer et al 2008) on the Swedish 1 m Solar Telescope (SST; Scharmer et al 2003) and the Interferometric BIdimensional Spectropolarimeter (IBIS; Cavallini 2006) on the Dunn Solar Telescope (DST; Dunn 1969), have made it possible to investigate spicules in unprecedented detail This has revealed various types of spicules: the classical type I spicule (Thomas 1948; Beckers 1968, 1972; Sterling 1998); a new, faster-evolving spicule entitled type II (De Pontieu et al 2007b); plus an on-disk counterpart.
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