Injection of m a gnetic helicity and chirality c hange in sunspot penumbral filaments
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Injection of magnetic helicity and chirality change in sunspot pen
umbral filaments
Jiangtao Su
National Astronomical Observatories of China
Helicity Thinkshop on Solar Physics 12-17 October Beijing
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Outline• Introduction: magnetic helicity injection (MHI) an
d solar activities;
• A initial study of relationships between MHI and major flares;
• MHI and chirality change of penumbral filaments in the magnetic polarity inversion line (PIL) region.
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Introduction• Magnetic helicity is a measure of twists, kinks, and interlinkag
es of magnetic field lines (Berger & Field 1984); It is almost preserved on a timescale less than the global diffusion time scale;
• Because of this conservation property, it has been suggested that Coronal Mass Ejections (CMEs) are needed to avoid the endless helicity accumulation in the corona (Rust 1994, 2001;Low 1996; Kusano et al. 2004; Zhang and Low 2005);
• Zhang et al. (2006) conjectured there is an upper bound on the total magnetic helicity that a force-free field can contain. Thus, the accumulation of magnetic helicity in excess of this upper bound would initiate a CME;
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• Recent theoretical work by Amari et al. (2003) suggests that a large enough helicity is a necessary but not sufficient condition for an ejection to occur, and this is supported by the observational work of Nindos & Andrews (2004);
• Whether or not that the corona helicity accumulation is important to the origin and initiation of CMEs is still hotly in debate (Spicer et al. 2003; Rust 2003; Rust & LaBonte 2005;Phillips et al. 2005);
• Therefore, knowledge of the magnetic helicity budgets in the solar active regions is essential for clarifying this issue (Green et al. 2002; Démoulin et al. 2002; Nindos et al. 2003; Mandrini et al. 2004; Georgoulis and LaBonte 2007);
• Untill now, the fundamental cause of solar flares is unkown, but Andrews (2003) has shown that virtually all X-class flares produce a coronal mass ejection (CME);
• Recently, LaBonte et al. (2007) found a necessary condition for the occurrence of an X-flare is that the peak helicity flux has a magnitude > 6×1036 Mx2 s-1, which should be an important flare index used for big flare prediction;
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• Moon et al. (2002a,b) believed that the sharp helicity change occurring over short timescales (half hour) can be a significant factor in triggering flares;
• Zhang et al. (2008) also found a sharp variation of the transport rate of magnetic helicity in AR 10930 during a X3.4 flare;
• Kusano et al. (2003) proposed annihilation of magnetic helicity as a triggering mechanism for solar flares. If the helicity is sharply reversed within a magnetic arcade, reconnection quickly grows in the helicity inversion layer, driving explosive dynamics;
• Yokoyama et al. (2003) studied flare activities in AR 8100 and found that most of the flare events occurred about half a day after the helicity injection rate changed its sign;
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• However, Sakurai & Hagino (2003) studied two X-class flares ARs and found the total magnetic helicity evolved slowly and did not show abrupt changes at the time of the flares;
• People have found during the flares, the profile of the spectral line being used for the magnetic measurements is distorted and the pulsive helicity changes were spurious (Qiu & Gary2003; Hartkorn & Wang 2004, e.g.);
• Park et al. (2008) investigated the variation of magnetic helicity around the times of 11 X-class flares. They found each of these major flares was preceded by a significant helicity accumulation and the helicity accumulates at a nearly constant rate then becomes nearly constant before the flares.
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• In this work, we revisit the relationships between rate of MHI and major x-class flares. With the Hinode data, we find a close relationship between MHI and chirality change in sunspot penumbral filaments.
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• Data: MDI/SOHO 96 minute longitudinal magnetograms;• Method: Local Correlation Tracking (LCT, Chae et al. 2001)
used to calculate dHm/dt.
ID Flares AR number Peak Time (UT)1 X5.7 on 2000 July 14 9077 10:24 2 X1.3 on 2001 Oct 25 9672 15:023 X18 on 2003 Oct 28 10486 11:104 X4.1 on 2005 Jan 17 10720 09:525 X3.4 on 2006 Oct 13 10930 02:40
dHm/dt and major x-class flares
List of the major flares
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A X5.7 occurred on 2000 July 14
NOAA 9077Before and after the x5.7 flare, the MHI rate evolves in a direction to decrease the magnitde of the previous MHI rate.
The helicity accumulates at a nearly constant rate (Park 2008), then becomes nearly constant after the flares. For this kind of constant rate, Magara & Tsuneta (2007) thought it is a saturation of helilcity transport.
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A X1.3 occurred on 2001 Oct 25
NOAA 9672
Same as NOAA 9077, but the magnitude of helicity injection rate first decreased, then increased.
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X18 on 2003 Oct 28
After the X18 flare, the helicity injection rate evolves in a direction to decrease the
magnitde of the previous MHI rate
NOAA 10486
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X4.1 on 2005 Jan 17
After the flare, the MHI rate changed its sign. It is similar to the active region of NOAA 8100 (Yokoyama et al. 2003).
NOAA 10720
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The first term in Eq. is usually associated to magnetic flux emergence, whereas the second is associated to shearing/twisting motions.
Which one is more important for the above evolutions?
/ 2 [( ) ( ) ]m p ps
dH dt d A v B A B v S
After (or before and after) the major flare, the MHI rate may evolve in a direction to decrease the magnitde of the pre-flare MHI rate. The expression for dHm/dt including two terms are:
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NO
AA
109
30
For NOAA 10930, three regions are selected to calculate dHm/dt:
(1) Frame1: large negative sunspot;(2) Frame2: two sunspots;(3) Frame3: small positive sunspot.
Frames 1 and 3 exclude the magnetic PIL region;
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dhm/dt in PIL region should be nearly equal to the one in Frame2 extracting those in Frames 1 and 3.
PIL region = Frame2 - Frame1+Frame3
After the flare, the MHI rate in Frames 1 and 3 did not change much, while that in Frame2 evolves in a direction to decrease the magnitde of the previous MHI rate and at last change its sign, which was mainly caused by the change of MHI rate in PIL region.
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Using the formula for the MHI rate Magra & Tsuneta (2007) and have obtained the similar results.
2/ /m sdH dt v L ,
Magra & Tsuneta (2007)
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MHI and chirality change in sunspot penumbral filaments in NOAA 10930
Averged αz in largepositive sunspot
Averaged αz in small negative sunspot
Su et al. (2009)
X3.4
flar
e
The penumbral filaments changing their chirality occurred in the rising stage of averged αz (MHI).
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Chirality change in the filaments of the PIL region in NOAA 10930
Chirality changed from right- to left-handedness
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Right-handed filaments
Left-handed filaments
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Splitting of a right-handed filament
Birth of a left-handed Filament
Dec-10
Dec-11
Expanding
Shrinking
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Filament screw pinch varying
At Cut4 pinch increasing:
396 , 475, and 1030 km;
At Cut5 pinch decreasing:
2580, 1988, and 806 km.
4 5
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z mapsLocal twist
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Total positive helicity decreased while total negative helicity increased.
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3
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Counter-clockwise rotation of the positive sunspot could inject negative helicity to the corona, which may dir
ectly lead to the filament change their chirality.
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Evidences of chirality change of the Filaments
1. Untwisting of penumbral filaments: The expansion of a filament, the separation of the feat
ures, and the increase of the screw pinch.
2. Chirality change of the filaments: The shrinking of a filament, the convergence of the fea
tures, and the decrease of the screw pinch.
3. Positive helicity decreased while negative helicity increased in response to a sunspot rotating, which injected negative helicity to the corona (photosphere).
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Thanks for your attention!