The Acceleration Process of a Solar Quiescent Filament in the Inner Corona

Coronal mass ejections (CMEs) are frequently associated with filament eruptions. Theoretical studies propose that both magnetic reconnection and ideal magnetohydrodynamic instability of magnetic flux ropes can convert coronal magnetic energy into the filament/CME kinetic energy. Numerical simulations and analytical considerations demonstrate that both mechanisms can have significant contributions to the filament/CME acceleration. Many observational studies support that reconnection plays an important role during the acceleration, while it remains open how to resolve observationally the contribution of the ideal instability to the acceleration. On the other hand, it is difficult to separate and compare their contributions through observations as both mechanisms often work in a close time sequence. In this Letter, the above issues are addressed by analyzing the eruption process of a quiescent filament. The filament started to rise from similar to 00:00 UT on 2011 December 25, 20 minutes earlier than the starting time of the flare impulsive phase (similar to 00:20 UT), and reached the maximum velocity at the flare peak time (similar to 00:50 UT). We divide the acceleration process into two stages, corresponding to the pre-flare and flare impulsive phases, respectively. The analysis indicates that an ideal flux-rope instability is dominant in the first stage, while reconnection below the flux rope becomes important during the second stage, and both mechanisms may have comparable contributions to the net acceleration of the filament.