1. The Relation between Filament Skew Angle and Magnetic Helicity of Active Regions Masaoki HAGINO, Y.J. MOON (Korea Astronomy and Space Science Institute) and Takashi SAKURAI (National Astronomical Observatory of Japan) The first Chinese-Korean Solar Physics Workshop July 9-13,2005

2. Contents ・ Introduction ・ data ・ Analysis Ⅰ (Chromospheric chirality and Coronal Chirality) ・ Result Ⅰ ・ Analysis Ⅱ (Skew angle and Photospheric Helicity) ・ Result Ⅱ ・ Summary ・ Future Works

3. Introduction The first Chinese-Korean Solar Physics Workshop July 9-13,2005 Skew angle : between orientation of overlaying loops and polarity inversion line(PIL).

4. Sakurai et al. found that a sheared coronal loop changed to a relaxed magnetic configuration during a flare. (Sakurai et al. 1992, PASJ, 44L.123) Sigmoidal loops or ‘Sigmoid’ had been observed by the soft X-ray telescope(SXT) aboard Yohkoh. (Sigmoid: Rust and Kumar, 1994, Solar phys, 155, 69 Yohkoh: Ogawara et al. 1991, Solar phys, 136, 10)

5. Filament chirality is defined by the relation between the spine of filament and the filament barbs. A filament whose axial field is directed rightward when viewed by an observer at the positive polarity side is called ‘dextral’. (Martin, 1998,Solar phys, 182, 107) + + + + dextralsinistral Examples of sinistral (left panels) and dextral (right panel) filaments, showing the direction of their barbs. (Big Bear Solar Observatory)

6. Martin et al. defined the chirality of H α filaments by using their structure (barbs and filament channels) and longitudinal magnetograms. They found the hemispheric rule of filament chirality. (Martin et al., 1994, Solar surface Magnetism, Kluwer Academic Publ., 433, 303) Sinistral filamentsDextral filaments

7. van Ballegooijen et al.(1998, ApJ, 501, 866) simulated the evolution of the chirality of the bipolar magnetic field. They used a skew to characterize filament chirality. In this study, they concluded that hemispheric helicity rule may reverse its sign after the polar field polarity reversal. This suggestion disagree with our result on the solar cycle independence (Hagino & Sakurai, 2005, PASJ accepted).

8. The objective of this study is to examine the relationship between magnetic helicity and skew between orientation of sigmoid and polarity inversion line (PIL). In order to achieve this purpose, we measure skews of PILs and coronal loops. We will focus our attention on Solar Active Region Skews. Motivation

9. Data The first Chinese-Korean Solar Physics Workshop July 9-13,2005 Vector magnetograms : SFT/MTK Longitude magnetograms : MDI/SOHO H-alpha image : BBSO EUV 171A image : TRACE Soft X-ray image : SXT/Yohkoh

10. Data selection We selected 33 active regions. ・ Longitude ±30° ←avoid Projection effect ・ Mitaka Observation ←the helicity calculation need vector magnetograms ・ TRACE Observation

11. Magnetogram (MDI/SOHO)

12. H alpha (BBSO)

13. Polarity Inversion Line (PIL)

14. EUV 171 (TRACE)

15. PIL Polarity Inversion Line (PIL)

16. Analysis Ⅰ The first Chinese-Korean Solar Physics Workshop July 9-13,2005 Chromospheric chirality and Coronal Chirality

17. Chromospheric chirality Viewed from positive polarity side of PIL, filament channels is dextral(sinistral) if the fibril go to right(left) from the positive polarity, respectively. Martin, S.F. 1994, BAAS, 26, 1552

18. Coronal Chirality Chae, 2000, ApJ, L115 In EUV image, filaments have bright and dark threads. This character means overlying and underlying threads. Chae applied this concept to the coronal chirality of filaments. PositiveNegative

19. Results Ⅰ The first Chinese-Korean Solar Physics Workshop July 9-13,2005

20. In our data, Sinistral Hα filaments show Positive Coronal Chirality, Dextral Hα filaments show negative coronal chirality.

21. Analysis Ⅱ Skew angle and Photospheric Helicity

22. Using gradient longitudinal magnetic fields and a limitation within ±150G, we look for polarity inversion line(PIL). In the case of island spots between main spots, we used smoothing and mask of these small spots near the PIL line. Moreover, in order to focus on PIL between main sunspots, we selected an area by hand. Finally, we decided a line, adopted by the linear fitting method about above PILs. We defined the PIL angle against the sunspot axis. Detection of a PIL

23. PIL angle starting point negative angle Clock-wise rotation positive angle Counter Clock-wise rotation

24. Polarity Inversion Line (PIL)

25. PIL angle

26. Using soft X-ray image(removed saturations) observed by Yohkoh SXT, we identified only a brightest coronal loop. If we assume that these bright pixels distribute on a 2D plane, we can measure a coronal loop tilt angle against sunspot axis, used by the linear fitting method. Detection of Coronal Loop angle

27. Coronal loop angle starting point Clock-Wise rotate negative angle Counter Clock-Wise rotate positive angle

28. Coronal loop angle (Soft X-ray/Yohkoh)

29. Definition of Skew angle The acute angle between the PIL and the coronal loop axis. The sign of chirality in this study used Martin’s cartoon (1998), i.e. if the loops cross over the PIL in the sense of threads of a left(right)-hand screw, they defined the loops as left(right)-skew.

30. Photospheric Helicity Fitting of the linear force-free field to the observed transverse field and finds the best α. Although magnetic fields are not force-free fields at the photosphere, we use force-free α as proxy.

31. Results Ⅱ The first Chinese-Korean Solar Physics Workshop July 9-13,2005

32. Hemispheric tendencies Hemispheric Distribution of Skews and Helicities Northern Hemisphere  Left-Skew  Negative helicity Southern Hemisphere  Right-Skew  Positive helicity

33. Hemispheric skews

34. Hemispheric helicities

35. Solid: mean dashed: variance Skew angle vs. Helicity

36. Summary The first Chinese-Korean Solar Physics Workshop July 9-13,2005

37. The relationship between filament chirality by Hα filament channels and by TRACE EUV171 observations : Dextral filament = Negative helicity Sinistral filament = Positive Helicity This result agree with Chae (2000), but does not support the prediction made by Martin and McAllister(1997). Martin and McAllister showed opposite sign between filament chirality and coronal skew by their model. Relation between skews and magnetic helicities in ARs shows a weak anti-correlation. A small skew angle region tends to have a large helicity obtained from the photosphere, and a large skew angle has a small helicity. Namely, in a highly sheared region, the PIL is parallel to the coronal loop axis.

38. Hemispheric tendency

39. Future Works The first Chinese-Korean Solar Physics Workshop July 9-13,2005

40. ・ We have to extend chromospheric(Hα) and Coronal(EUV) chirality data and carefully check signs of chiralities. ・ By fitting the coronal structure and the force-free parameter α (Pevtsov et al., 1997, ApJ, 481, 973), I want to examine the relation between coronal helicities and skew angles. ・ Our results will be individually compared with flare activities and CMEs. 謝謝