Non-thermal line broadening due to braiding-induced turbulence in solar coronal loops

TL;DR

This study uses a 3D MHD model to simulate magnetic braiding in solar coronal loops, successfully reproducing observed non-thermal line broadening and non-Gaussian spectral features linked to turbulence and plasma heating.

Contribution

It introduces a self-consistent model connecting magnetic braiding-induced turbulence to observed spectral line broadening in coronal loops.

Findings

Non-thermal widths range from 15 to 20 km/s.

Spectral widths are independent of field of view size.

Spectra exhibit non-Gaussian wings with 10-20% enhancement.

Abstract

Aims: Emission line profiles from solar coronal loops exhibit properties that are unexplained by current models. We investigate the non-thermal broadening associated with plasma heating in coronal loops that is induced by magnetic field line braiding. Methods: We describe the coronal loop by a 3D magnetohydrodynamic model of the turbulent decay of an initially-braided magnetic field. From this we synthesize the Fe XII line at 193 Angstroms that forms around 1.5 MK. Results: Key features of current observations of extreme UV lines from the corona are reproduced in the synthesised spectra: (i) Typical non-thermal widths range from 15 to 20 km/s. (ii) The widths are approximately independent of the size of the field of view. (iii) There is a correlation between line intensity and the non-thermal broadening. (iv) Spectra are found to be non-Gaussian, with enhanced power in the wings of order 10-20%. Conclusions: Our model provides an explanation that self-consistently connects the heating process to the observed non-thermal line broadening. The non-Gaussian nature of the spectra is a consequence of the non-Gaussian nature of the underlying velocity fluctuations, interpreted as a signature of intermittency in the turbulence.