Partial Eruption, Confinement, and Twist Buildup and Release of a Double-decker Filament

TL;DR

This study examines a failed partial filament eruption in NOAA AR 12104, revealing a double-decker structure with twist buildup and release, using multiwavelength observations and magnetic modeling to understand the eruption dynamics.

Contribution

It provides the first detailed analysis combining observations and magnetic modeling to understand the partial eruption and twist dynamics of a double-decker filament system.

Findings

Only the upper filament segment erupted and twisted, while the lower remained stable.

The flux rope reached the torus instability height, triggering eruption.

Reconnection destroyed the flux rope and transferred its twist to overlying fields.

Abstract

We investigate the failed partial eruption of a filament system in NOAA AR 12104 on 2014 July 5, using multiwavelength EUV, magnetogram, and H$\alpha$ observations, as well as magnetic field modeling. The filament system consists of two almost co-spatial segments with different end points, both resembling a C shape. Following an ejection and a precursor flare related to flux cancellation, only the upper segment rises and then displays a prominent twisted structure, while rolling over toward its footpoints. The lower segment remains undisturbed, indicating that the system possesses a double-decker structure. The erupted segment ends up with a reverse-C shape, with material draining toward its footpoints, while losing its twist. Using the flux rope insertion method, we construct a model of the source region that qualitatively reproduces key elements of the observed evolution. At the eruption onset, the model consists of a flux rope atop a flux bundle with negligible twist, which is consistent with the observational interpretation that the filament possesses a double-decker structure. The flux rope reaches the critical height of the torus instability during its initial relaxation, while the lower flux bundle remains in stable equilibrium. The eruption terminates when the flux rope reaches a dome-shaped quasi-separatrix layer that is reminiscent of a magnetic fan surface, although no magnetic null is found. The flux rope is destroyed by reconnection with the confining overlying flux above the dome, transferring its twist in the process.