Two-stage primary acceleration in filament initial eruption under a fan-spine magnetic configuration

TL;DR

This study analyzes the two-stage acceleration process of a filament eruption under a fan-spine magnetic configuration, revealing the roles of magnetic reconnection and flux rope growth in triggering eruptions.

Contribution

It provides a detailed observational analysis of the multi-stage acceleration process during filament eruption under a fan-spine magnetic structure, highlighting the role of magnetic reconnection.

Findings

Filament experienced two distinct acceleration stages with different flare events.

Hot channel and magnetic flux rope growth are linked to eruption stages.

Magnetic reconnection above and below the filament drives the acceleration phases.

Abstract

Understaning the filament rising process is crucial for unveiling the triggering mechanisms of the coronal mass ejections and forecasting the space weather. In this paper, we present a detailed study on the filament initial eruption under a fan-spine structure. It was found that the filament underwent two distinct acceleration stages corresponding to a calss M1.0 and M4.6 flare event, respectively. The first acceleration stage commenced with the filament splitting, after which the upper portion was subsequently heated being a hot channel and slow rose at an average speed of 22 km/s. A set of hot reverse C-shaped loops appeared repeatedly during the filament splitting and a hook structure was recognized at this phase, suggesting ongoing growth of the magnetic flux rope (MFR). When it reached a certain altitude, the hot channel appeared to get into a quasi-static phase with its upper edge seriously decelerated and lower edge expanding downward. Approximately 30 minutes later, as a distinct annular ribbon appeared outside the hook structure, the hot channel rose again at a velocity over 50 km/s accompanied with rapid footpoints drifting, and experienced the second acceleration stage with its axial flux increased to 1.1 X 10^{21} Mx. It is deduced that the filament initial eruption under a magnetic dome possess multi kinetic process. We suggest that the magnetic reconnection taken place within and beneath the filament continues to trigger the growth of pre-eruptive MFR and the first acceleration, when the magnetic reconnection above the filament plays a key role in the second acceleration.