On the multi-threaded nature of solar spicules

TL;DR

This study reveals the multi-threaded and torsional dynamics of solar spicules using high-resolution observations, showing asymmetric spectra and internal sub-structures that suggest complex flows and motions in the chromosphere.

Contribution

It provides new evidence of the multi-threaded and asymmetric spectral features of spicules, highlighting their complex internal dynamics and torsional components.

Findings

Many spicules display asymmetric spectra with multiple peaks.

Average velocity difference between components is 20-30 km/s.

Spectral tilts indicate complex internal motions within spicules.

Abstract

A dominant constituent in the dynamic chromosphere are spicules. Spicules at the limb appear as relatively small and dynamic jets that are observed to everywhere stick out. Many papers emphasize the important role spicules might play in the energy and mass balance of the chromosphere and corona. However, many aspects of spicules remain a mystery. In this Letter we shed more light on the multi-threaded nature of spicules and their torsional component. We use high spatial, spectral and temporal resolution observations from the Swedish 1-m Solar Telescope in the H{\alpha} spectral line. The data targets the limb and we extract spectra from spicules far out from the limb to reduce the line-of-sight superposition effect. We discover that many spicules display very asymmetric spectra with some even showing multiple peaks. To quantify this asymmetry we use a double Gaussian fitting procedure and find an average velocity difference between the single Gaussian components to be between 20-30 km s$^{-1}$ for a sample of 57 spicules. We observe that spicules show significant sub-structure where one spicule consists of many 'threads'. We interpret the asymmetric spectra as line-of-sight superposition of threads in one spicule and therefore have a measure for a perpendicular flow inside spicules which will be important for future numerical model to reproduce. In addition we show examples of {\lambda}-x-slices perpendicular across spicules and find spectral tilts in individual threads providing further evidence for the complex dynamical nature of spicules.