Evolution of Barb-Angle and Partial Filament Eruption

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] • 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: • Chirality (Helicity or Twist) exists in all solar magnetic features (Rust & Kumar 1994; Low & Hundhausen 1995; Martin 1998) • 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). Dextral Sinistral Chirality patterns of filaments (Martin 1998)

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

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. 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. • Definition of barb angle

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. No BBSO data 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.

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

9. The second phase of barb evolution : a fall of barb-angle The angle 900 ? Ha center Ha center One can see from the fitted line in evolving Figure, that when the barb angle decreased nearly to 900 (there was nearly no dextral component), the U-shaped filament began to erupt. FMT Ha Ha center Ha-Blue (-0.8Å) The regions A and B Weakened occurred again. FMT Ha images taken at Hida Observatory (Kurokawa et al. 1995)

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

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. Chirality Changing in partial filament Magnetic field reconnecting in filament or coronal arcade Partial filament eruption Interconnections weakened in filament 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. The process of partial eruption

13. Thanks a lot !