The Relation between Filament Skew Angle and Magnetic Helicity of Active Regions Masaoki HAGINO,

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

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

4. Sigmoidal loops or ‘Sigmoid’ had been observed by the softX-ray telescope(SXT) aboard Yohkoh. (Sigmoid: Rust and Kumar, 1994, Solar phys, 155, 69 Yohkoh: Ogawara et al. 1991, Solar phys, 136, 10) 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)

5. + + dextral sinistral 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) Examples of sinistral (left panels) and dextral (right panel) filaments, showing the direction of their barbs.(Big Bear Solar Observatory)

6. Sinistral filaments Dextral filaments Martin et al. defined the chirality of Hα filaments by using theirstructure (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)

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. Motivation 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.

9. The first Chinese-Korean Solar Physics Workshop July 9-13,2005 Data 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. Polarity Inversion Line (PIL) PIL

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

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

18. Positive Negative Coronal Chirality 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. Chae, 2000, ApJ, L115

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

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. Detection of a PIL 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 nearthe 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 methodabout above PILs. We defined the PIL angle against the sunspot axis.

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

24. Polarity Inversion Line (PIL)

25. PIL angle

26. Detection of Coronal Loop angle 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.

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

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

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

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

33. Hemispheric skews

34. Hemispheric helicities

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

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

37. The relationship between filament chirality by Hα filamentchannels and by TRACE EUV171 observations : Dextral filament = Negative helicity Sinistral filament = Positive Helicity This result agree with Chae (2000), but does not supportthe prediction made by Martin and McAllister(1997). Martin and McAllister showed opposite sign betweenfilament 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 helicityobtained from the photosphere, anda 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. The first Chinese-Korean Solar Physics Workshop July 9-13,2005 Future Works

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