The Observational Study of Activations and Eruptions of Solar Filament

The study of solar filament activations and eruptions is important not only in understanding formation and stability of filaments but also in understanding violent solar eruptions such as flares and coronal mass ejections. In the present paper, the observational and theoretical progresses in the more recent study of the structure,dynamics and magnetic field configuration of the filament are introduced.The observational characteristics, disturbing agents, possible driving mechanisms and theoretical models of the filament instability are also summarized. It is studied for the detailed morphological and dynamic evolution of several disturbed filaments, the relevant changes of photospheric magnetic field and coronal structure, as well as the development of associated flares. The main results are included as follows: 1.Once filaments are disturbed, the presence of twisted structure and motion is not an uncommon result, and the filament twist needs not to be great enough to lead to an eruption. The fact suggests that twisted magnetic field may commonly exist in disturbed filament. For the first time,we have found a unique "velocity rope" pattern during the activating process of a quiescent filament, which clearly revealed the twisted field in the disturbed filament. 2.In study of the filament disturbances in an active region, we have showed that the filament underwent successive activation and each disturbance was followed by a flare, but it did not erupt or disappear. For the first time, we have fount that the activation of the whole filament could be resulted from the disturbance of the one of twisted filament threads, while the other threads remain nearly stationary. 3.For the first time, we have identified that the helical structure appeared in an eruptive sinistral filament was left-helical one. Such identification is consistent with Martin McAllister's prediction (1997) but at odds with Rust Kumar's (1994) assumption; we further have refered that the magnetic field of filaments is not helical in their quiescent status and helical structure during filament disturbance is formed by the magnetic reconnection between non-helical structures. 4.The filament disturbances are closely associated with the photospheric displacement and changes of the photospheric magnetic field in the filament channel. The pore birth and movement, the sunspots squeeze and shear, the magnetic flux emergence and cancellation may be all contributed to the loss of the filament stability. 5.The cause of the filament destabilization is interpreted as the steady cancellation reconnection in the photosphere layer. Such pre-eruptive reconnection leads to the accumulation of the magnetic flux and complexity in the filament via inducing the current and changing the magnetic field of the filament to the photosphere, hence directly relevant to filament disturbances. In the study of the eruption of an active-region filament, which was obviously driven by an emerging bipole, we have found that the eruption was due to the interaction between the bipole and the X-ray loops overlying the filament, and we have provided clear evidence that slowly photospheric reconnection in their interface occurred during the bipole emergence.