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
40
Embed
The Relation between Filament Skew Angle and Magnetic Helicity of Active Regions Masaoki HAGINO,
The first Chinese-Korean Solar Physics Workshop July 9-13,2005. 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). - PowerPoint PPT Presentation
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
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)
++++
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
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
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
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.