1. Evolution of Barb-Angle and Partial Filament Eruption J.T. Su [1,2], Y. Liu [2], H.Q. Zhang [1], H. Kurokawa [2] V. Yurchyshyn [3] (1)National Astronomical Observatories, Chinese Academy of Sciences (2) Kwasan and Hida Observatories, Kyoto University (3)Big Bear Solar Observatory, New Jersey Institute of Technology

2. Introduction: (1) Chirality (Helicity or Twist) exists in all solar magnetic features (Rust & Kumar 1994; Low & Hundhausen 1995; Martin 1998) (2) These features belong to either dextral patten or sinistral patten. Martin (1998) pointed out that different chirality patterns can not co-exist in one magnetic feature(Martin 1998). Chirality patterns of filaments (Martin 1998) Sinistral Dextral

3. (3) However, Pevtsov et al. (2003) found some filaments, in quiet or active regions, exhibit both sinistral and dextral barbs. (4) Tracing the evolving process of one certain magnetic feature may help to eliminate the contradictions. Pevtsov et al. (2003)

4. A: Liu and zhang (2002) studied the evolution of a delta spot. Their results clearly demonstrate that the helicity reversal occurred in magnetic features of a delta-configuration, then the subsequent disintegration of the sunspot probably ascribed to this reversal behavior. B: Wang et al. (2004) found the flare/CME initiation site is characterized by close contact with magnetic flux of the opposite helicity coinciding with observed flux cancellation. In this work, we study the angle evolution of a main barb born in the U-shaped filament. Observation:

5. Partial filament: Dextral The whole U-shaped filament and the filament nearby to it are sinistral by the definitions of Martin (1998). BBSO Ha

6. Definition of barb angle First, we outline the intensity contour of filament and fix the minimum intensity level of each image. Second, we plot two axis lines of the barb and the filament to be analyzed. Last, we plot a circle with the cross- point of the two lines as the center and the distance between the barb and the center as the radius. The value of the angle a-o-b marked in the plot is available now, which is acute or obtuse.

7. The angle evolution can be divided into two phases: (1)a rise from the acute one to the obtuse one and (2) a fall of the angle. The separate time is ~ on 22:10 UT. Note that the changes of the angle reflected the evolution of the barb chirality and furthermore the helicity of the part of filament bearing the barb. No BBSO data

8. The barb chirality evolved from sinistral to dextral. The regions A and B Weakened. BBSO Ha The first phase of barb evolution: a rise of barb-angle

9. FMT Ha images taken at Hida Observatory (Kurokawa et al. 1995) Ha center Ha-Blue (-0.8Å) The regions A and B Weakened occurred again. One can see from the fitted line in evolving Figure, that when the barb angle decreased nearly to 90 0 (there was nearly no dextral component), the U- shaped filament began to erupt. The second phase of barb evolution : a fall of barb-angle The angle 90 0 ? FMT Ha

10. Before partial filament eruption, the magnetic cancellation occurred on the Photosphere. Partial filament eruption Magnetic Flux

11. FMT Ha FMT Ha-Blue EIT 195 However, no obvious brightenings appeared, it indicates that no magnetic cancellation occurred on the Chromosphere or Corona.

12. Conclusions: (1)Helicity of opposite sign was formed in the filament, it would be likely to weaken the interconnections of the whole magnetic system. (2) Different chirality patterns can not co-exist in one magnetic feature for longer time. Chirality Changing in partial filament Interconnections weakened in filament Partial filament eruption Magnetic field reconnecting in filament or coronal arcade The process of partial eruption

13. Thanks a lot !