Parallel plasma loops and the energization of the solar corona

TL;DR

This study uses high-resolution solar observations to examine the structure and energization of plasma loops in the Sun's corona, providing evidence against highly braided magnetic fields in these loops.

Contribution

It offers observational evidence that plasma loops in the solar corona are parallel and not highly braided, supporting models with significant magnetic dissipation.

Findings

Loops at different temperatures run in parallel with minimal offset.

No signatures of loops being twisted or braided around each other.

Supports models where magnetic stresses relax before reaching high braiding.

Abstract

The outer atmosphere of the Sun is composed of plasma heated to temperatures well in excess of the visible surface. We investigate short cool and warm (<1 MK) loops seen in the core of an active region to address the role of field-line braiding in energising these structures. We report observations from the High-resolution Coronal imager (Hi-C) that have been acquired in a coordinated campaign with the Interface Region Imaging Spectrograph (IRIS). In the core of the active region, the 172 A band of Hi-C and the 1400 A channel of IRIS show plasma loops at different temperatures that run in parallel. There is a small but detectable spatial offset of less than 1 arcsec between the loops seen in the two bands. Most importantly, we do not see observational signatures that these loops might be twisted around each other. Considering the scenario of magnetic braiding, our observations of parallel loops imply that the stresses put into the magnetic field have to relax while the braiding is applied: the magnetic field never reaches a highly braided state on these length-scales comparable to the separation of the loops. This supports recent numerical 3D models of loop braiding in which the effective dissipation is sufficiently large that it keeps the magnetic field from getting highly twisted within a loop.