Evolution of barb angle and filament eruption

Hα observations of a quiescent U-shaped filament were obtained at Big Bear Solar Observatory and at Hida Observatory with the Flare Monitoring Telescope. The filament was located in the southern hemisphere on 1998 November 4. We study the evolution of the angle of a barb with respect to the axis of the filament and find the evolution can be divided into two phases: a rise from the acute phase to the obtuse phase and a fall. Thus, this indicates that the chirality of this barb changes with time. Moreover, in the process of evolution, we find that interconnection of the part of the filament bearing the barb with the whole filament became either weakened or strengthened. We impute the final eruption of the filament to the chirality evolution of the barb.