Pre-eruption Splitting of the Double-Decker Structure in a Solar Filament

TL;DR

This study investigates the pre-eruption splitting process of a solar filament, revealing a double-decker structure formed by flux cancellations, and details the dynamic stages leading to partial eruption.

Contribution

It provides the first detailed observation of the three-stage evolution of a pre-eruption filament splitting and supports the double-decker flux bundle model.

Findings

Filament splitting occurs in three stages with distinct dynamics.

The upper branch erupts while the lower remains stable.

Formation of the double-decker structure is linked to magnetic flux cancellations.

Abstract

Solar filaments often erupt partially. Although how they split remains elusive, the splitting process has the potential of revealing the filament structure and eruption mechanism. Here we investigate the pre-eruption splitting of an apparently single filament and its subsequent partial eruption on 2012 September 27. The evolution is characterized by three stages with distinct dynamics. During the quasi-static stage, the splitting proceeds gradually for about 1.5 hrs, with the upper branch rising at a few kilometers per second and displaying swirling motions about its axis. During the precursor stage that lasts for about 10 min, the upper branch rises at tens of kilometers per second, with a pair of conjugated dimming regions starting to develop at its footpoints; with the swirling motions turning chaotic, the axis of the upper branch whips southward, which drives an arc-shaped EUV front propagating in the similar direction. During the eruption stage, the upper branch erupts with the onset of a C3.7-class two-ribbon flare, while the lower branch remains stable. Judging from the well separated footpoints of the upper branch from those of the lower one, we suggest that the pre-eruption filament processes a double-decker structure composed of two distinct flux bundles, whose formation is associated with gradual magnetic flux cancellations and converging photospheric flows around the polarity inversion line.