Helical Kink Instability in a Confined Solar Eruption

TL;DR

This study models a confined solar eruption driven by helical kink instability, successfully matching observed features and revealing two-phase magnetic reconnection processes that differ from ejective eruptions.

Contribution

It demonstrates that helical kink instability can explain confined solar eruptions and details the reconnection phases, expanding understanding of eruption dynamics.

Findings

Model matches observed filament eruption properties.

Reconnection occurs in two distinct phases.

External field ratio and flux rope twist are constrained.

Abstract

A model for strongly writhing confined solar eruptions suggests an origin in the helical kink instability of a coronal flux rope which remains stable against the torus instability. This model is tested against the well observed filament eruption on 2002 May 27 in a parametric MHD simulation study which comprises all phases of the event. Good agreement with the essential observed properties is obtained. These include the confinement, terminal height, writhing, distortion, and dissolution of the filament, and the flare loops. The agreement is robust against variations in a representative range of parameter space. Careful comparisons with the observation data constrain the ratio of the external toroidal and poloidal field components to $B_\mathrm{et}/B_\mathrm{ep}\approx1$ and the initial flux rope twist to $\Phi\approx4\pi$. Different from ejective eruptions, two distinct phases of strong magnetic reconnection can occur. First, the erupting flux is cut by reconnection with overlying flux in the helical current sheet formed by the instability. If the resulting flux bundles are linked as a consequence of the erupting rope's strong writhing, they subsequently reconnect in the vertical current sheet between them. This reforms the overlying flux and a far less twisted flux rope, offering a pathway to homologous eruptions.