The instability and non-existence of multi-stranded loops, when driven by transverse waves

TL;DR

This study uses 3D MHD simulations to demonstrate that transverse wave driving causes coronal loop strands to become unstable and merge, challenging the traditional multi-stranded loop model in the solar atmosphere.

Contribution

The paper provides the first detailed simulation evidence that transverse waves destabilize and eliminate multi-stranded coronal loops, questioning their independent strand-based modeling.

Findings

Multi-stranded loops are unstable under transverse wave driving.

Kelvin-Helmholtz instability causes efficient plasma mixing.

Resulting loops exhibit a power-law density structure.

Abstract

In recent years, omni-present transverse waves have been observed in all layers of the solar atmosphere. Coronal loops are often modeled as a collection of individual strands, in order to explain their thermal behaviour and appearance. We perform 3D ideal MHD simulations to study the effect of a continuous small amplitude transverse footpoint driving on the internal structure of a coronal loop composed of strands. The output is also converted to synthetic images, corresponding to the AIA 171 A and 193 A passbands, using FoMo. We show that the multi-stranded loop ceases to exist in the traditional sense of the word, because the plasma is efficiently mixed perpendicularly to the magnetic field, with the Kelvin-Helmholtz instability acting as the main mechanism. The final product of our simulation is mixed loop with density structures on a large range of scales, resembling a power-law. Thus, multi-stranded loops are unstable to driving by transverse waves, and this raises a strong doubt on the usability and applicability of coronal loop models consisting of independent strands.