The Relation betweenFilament Skew Angle

andMagnetic Helicity of

Active Regions

Masaoki HAGINO,Y.J. MOON

(Korea Astronomy and Space Science Institute)

andTakashi SAKURAI

(National Astronomical Observatory of Japan)

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

Contents

・ Introduction

・ data

・ Analysis Ⅰ (Chromospheric chirality and Coronal Chirality)・ Result Ⅰ

・ Analysis Ⅱ (Skew angle and Photospheric Helicity)・ Result Ⅱ

・ Summary

・ Future Works

Introduction

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

Skew angle : between orientation of overlaying loops and polarity inversion line(PIL).

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 softX-ray telescope(SXT) aboard Yohkoh.(Sigmoid: Rust and Kumar, 1994, Solar phys, 155, 69 Yohkoh: Ogawara et al. 1991, Solar phys, 136, 10)

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)

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dextral sinistral

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

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)

Sinistral filaments Dextral filaments

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).

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

Data

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

Vector magnetograms : SFT/MTKLongitude magnetograms : MDI/SOHO

H-alpha image : BBSOEUV 171A image : TRACE

Soft X-ray image : SXT/Yohkoh

Data selection

We selected 33 active regions.

・ Longitude ±30° ←avoid Projection effect・ Mitaka Observation ←the helicity calculation need vector magnetograms・ TRACE Observation

Magnetogram (MDI/SOHO)

H alpha (BBSO)

Polarity Inversion Line (PIL)

EUV 171 (TRACE)

PILPolarity Inversion Line (PIL)

Analysis Ⅰ

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

Chromospheric chirality and Coronal Chirality

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

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.

Positive Negative

Results Ⅰ

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

Date NOAA Obs_time Latitude Longitude sunspot tilt Ha chiral firament PIL Tilt(spot) corona chiral CL Tilt (spot) Skew Mag type

19981103 8375 1:09:56 20.8 -17.1 42.40 sinistral ? -4.25 positive 76.14 9.60 b-g19981114 8384 5:22:11 -22.1 -18.3 -18.87 ? ? 38.36 ? 8.01 120.35 b19990212 8457 3:14:27 11 -24.9 21.19 ? ? 82.55 positive -13.99 -173.46 b19990314 8485 2:45:16 19.4 0.2 11.08 ? ? 51.14 negative 2.54 138.59 b-g19990707 8614 2:27:44 18.4 0.5 12.80 sinistral ? -31.43 ? 8.73 49.85 b19990803 8651 0:09:07 0.4 5.2 8.45 ? ? -30.66 ? -30.20 89.54 b-g19991028 8739 2:32:27 -8.5 23 -22.67 ? ? 5.25 ? -33.41 128.66 b-g-d20000115 8824 4:28:24 -15.6 -10.3 -8.65 ? exist 47.62 negative -40.48 178.10 b-g-d20000126 8844 0:45:09 6.2 29.6 22.52 sinistral ? -23.29 ? 22.18 44.53 b20000203 8851 2:00:53 22.7 -0.4 17.16 dextral exit 55.60 negative -28.40 174.00 b20000225 8882 2:56:41 -15.8 -24 5.31 sinistral ? 22.87 positive 5.68 107.18 b20000429 8970 0:26:46 -12.1 23 3.07 ? ? -12.30 ? -31.34 109.04 b-g20000529 9017 0:33:04 -9.7 -24.9 1.19 sinistral ? 23.61 ? 17.34 96.27 b-g20000709 9070 1:04:30 19.6 10.9 -5.36 dextral exist 51.84 negative -44.52 -173.64 b-g20000724 9097 3:00:01 8.4 -10.3 -19.00 dextral exist 41.87 ? -30.35 162.22 b-g20000922 9169 2:00:12 9.8 -24.7 -24.94 ? ? -4.53 ? -5.41 90.87 b-g-d20001024 9201 1:11:24 17.1 10.4 16.44 ? ? 42.26 ? -7.60 139.86 b20001117 9231 23:58:55 -20.5 -6.9 -10.83 dextral ? 64.16 ? -13.53 167.70 b20010208 9339 0:34:12 -12.1 -27.8 -10.01 ? exist -30.89 negative 7.06 52.05 b20010219 9354 0:19:37 -10.6 -2.6 9.46 sinistral exist -20.81 positive 7.62 61.57 b20010308 9368 0:27:28 18.3 18.2 10.01 ? ? -24.05 ? -23.89 89.84 b20010313 9373 3:20:00 -6.7 -26.6 -11.31 dextral ? -27.22 negative 10.94 51.84 b20010328 9393 6:26:00 12.9 -3.6 18.43 ? exist 62.18 negative -25.15 177.33 b-g-d20010410 9415 5:27:58 -23.6 9.1 -20.70 sinistral exist 4.31 ? 0.40 93.91 b-g-d20010427 9433 3:02:27 13.8 21.4 -8.13 dextral exist 44.54 ? -11.21 145.74 b-g-d20010506 9445 0:47:22 19.1 15.8 47.20 dextral exist -62.22 negative 25.92 1.85 b-g20010525 9463 0:00:50 9.4 12.8 19.75 ? ? -9.74 ? -0.99 81.25 b20010618 9503 0:22:34 9.8 -17 13.50 ? ? -4.89 ? 13.73 71.38 b-g20010629 9516 1:08:21 16.7 10 7.43 ? exist 40.43 ? -32.25 162.67 b20010817 9575 1:00:03 10.3 -8 12.03 dextral exist 54.93 ? 6.50 138.44 b20010905 9601 3:27:58 11.1 24.8 5.83 dextral exist 29.41 ? -20.50 139.91 b-g20011019 9661 1:06:02 11.6 22.3 90.00 dextral exist 3.50 ? 77.68 15.82 b-g-d20011026 9678 1:27:05 4.9 -16.8 17.78 ? exist -43.31 ? -12.07 58.76 b-g-d

NOAA Ha chirality coronal chirality

8375 sinistral positive(II)8851 dextral negative(III)8882 sinistral positive(I)9070 dextral negative(IV)9354 sinistral positive(I)9373 dextral negative(III)9445 dextral negative(IV)

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

Analysis Ⅱ

Skew angle and Photospheric Helicity

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.

Detection of a PIL

PIL angle

starting point

negative angle

Clock-wise rotation

positive angle

CounterClock-wise rotation

Polarity Inversion Line (PIL)

PIL 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.

Detection of Coronal Loop angle

Coronal loop angle

starting point

Clock-Wise rotate

negative angle

CounterClock-Wise rotate

positive angle

Coronal loop angle (Soft X-ray/Yohkoh)

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.

Photospheric Helicity

Fitting of the linear force-free field to the observed transverse fieldand finds the best α.

Although magnetic fields are not force-free fieldsat the photosphere, we use force-free α as proxy.

Results Ⅱ

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

Hemispheric tendencies

Hemispheric Distribution of Skews and Helicities

Northern Hemisphere Left-Skew Negative helicitySouthern Hemisphere Right-Skew Positive helicity

Hemispheric skews

Hemispheric helicities

Solid: mean dashed: variance

Skew angle vs. Helicity

Summary

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

The relationship between filament chirality by Hα filamentchannels and by TRACE EUV171 observations : Dextral filament = Negative helicity Sinistral filament = Positive HelicityThis 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.

Hemisphere Ha Chirality EUV Chirality Skew HelicityNorthern dextral negative Left α <0Southern sinistral positive Right α >0

Hemispheric tendency

Future Works

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

・ 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.

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