Fine strand-like structure in the solar corona from MHD transverse oscillations

TL;DR

This paper demonstrates that small amplitude transverse MHD waves can generate strand-like structures in the solar corona through Kelvin-Helmholtz instabilities, providing an alternative explanation for observed fine structures.

Contribution

It introduces a novel mechanism where low amplitude transverse waves produce strand-like features via instabilities, differing from the traditional nanoflare model.

Findings

Strand-like structures can form from low amplitude waves within a few periods.

Vortices and line-of-sight effects produce observable strands at high resolution.

Strands last about a period and match observed widths in the corona.

Abstract

Current analytical and numerical modelling suggest the existence of ubiquitous thin current sheets in the corona that could explain the observed heating requirements. On the other hand, new high resolution observations of the corona indicate that its magnetic field may tend to organise itself in fine strand-like structures of few hundred kilometres widths. The link between small structure in models and the observed widths of strand-like structure several orders of magnitude larger is still not clear. A popular theoretical scenario is the nanoflare model, in which each strand is the product of an ensemble of heating events. Here, we suggest an alternative mechanism for strand generation. Through forward modelling of 3D MHD simulations we show that small amplitude transverse MHD waves can lead in a few periods time to strand-like structure in loops in EUV intensity images. Our model is based on previous numerical work showing that transverse MHD oscillations can lead to Kelvin-Helmholtz instabilities that deform the cross-sectional area of loops. While previous work has focused on large amplitude oscillations, here we show that the instability can occur even for low wave amplitudes for long and thin loops, matching those presently observed in the corona. We show that the vortices generated from the instability are velocity sheared regions with enhanced emissivity hosting current sheets. Strands result as a complex combination of the vortices and the line-of-sight angle, last for timescales of a period and can be observed for spatial resolutions of a tenth of loop radius.