The quantitative analysis of the spiral chirality of penumbral filament

1

Helicity Thinkshop on Solar Physics, Oct. 2013, Beijing

Liu J.H. , Su J.T. et al.Shijiazhuang University

Key Laboratory of Solar Activity, NAOC

Outlines

• 1. Background of penumbral filament(fibrals)

and Screw pinch instability

• 2. Unwinding and twist change in penumbral fil

aments (Su et al. 2010, ApJ, 710, 170);

• 3. Screw pinch instability and penumbral

filaments charality;

• 4. Screw pinch instability and a C2.6 flare.

1. Background of penumbral filaments(fibrals)

Uncombed model: It takes the penumbra as a collection of horizontal flux tubes in a more vertical background field. (Solanki & Motavon 1993).

Gap model: A field-free model which takes the filaments as the non-magnetized convecting hot gas protruding into the background of potential magnetic fields. (Spruit and Scharmer 2006; Scharmer and Spruit 2006).

By studying the expasion, unwinding, shrinking, twisting motion of the penumbral filament, Su et al. consider that the penumbral filaments are the twisted magnetic flux tubes in nature. (Su et al. 2010)

There are two schematic models are intensely studied regarding the origin of the penumbral filaments.

4

pitch :the distance in which the field line makes one revolution around the flux tube, is

22( )

tanzRBR

h RB

R is the radius of the flux tube and L is its length. (Priest 1984, Ryutova et al. 2008)

“screw pinch” configuration

Long, magnetic cylindrical flux tubes are subject to helical instabilities, and a magnetic flux tube with both azimuthal and axial components twists into a kinked helical shape.

Background of Screw pinch instability

5

2 zRB hq

LB L

1q

Safty factor:

The screw pinch instability turns on when the safety factor is

Screw pinch instability

6

1. (h/R) > 2.62, the magnetic field components preserve their initial direction and chirality.

2. 1.63 < (h/R) < 2.62, the axial magnetic field reverses but the chirality of the filament remains the same.

3. 1.14 < (h/R) 1.63, the axial magnetic field reversal is accompanied by reversed chirality.

For the kink mode m=1:

Ryutova , Berger & Title 2008 Model:

7

Considering the chirality Only and for the kink mode m=1:

• (h/R) >1.63, the chirality of the filament remains the same.

• 1.14<(h/R) <1.63, the chirality of the filament reverse.

• (h/R) <1.14, very strong twist, will lead to disruption of the filament.

2. Unwinding and twist change in penumbral filaments

Twist from right- to left-handedness

G-band images of AR NOAA 10930 ，red frame mark the position where the penumbra filament studied, A right-handed filament expanding and unwinding, a left-handed filament come into being, shrinking and twisting .

Su et al. 2010, ApJ, 710, 170

TVtxT

BRBRh z

)/(

/2)(

Using the Space-time image, the screw pitch can be deduced (Su et al. 2010):

Considering the penumbral filaments as twisted flux in nature, the charality development and reversal, the unwinding and twisting motion of the penumbral filaments, connecte with the Screw pinch instability. So does the flare.

High resolution observing evidences and quantitative analysis are shown as following.

Quantitative analysis on the relationship between Screw pinch instability and penumbral filaments charality, and flare

11

Expansion and unwinding stage: right-handed twist

Temporal development of the G-band images SOT/Hinode.

3. Screw pinch instability and penumbral filaments charality

12

h/R and h/L: on expansion and unwinding stage

Time T(m) h(Km) R(Km) L_av(Km) h/R h/L

11:48~12:06 20 396 347 1515 1.14 0.2612:06~12:24 24 475 395 1515 1.20 0.3112:30~13:27 52 1030 646 1515 1.59 0.68

11:48~13:27 UT Dec 101.14<(h/R) <1.63, the filament unwind rapidly, and its chirality reversed about 6 hours later.

The increasing trend of h/R reveals the unwinding motion of the punumbra filament.

The increasing trend of h/L imply that, accompany with the unwinding motion, the instability decrease.

This is consistent with the theory of Ryutova et al. 2008.

13

Shrinking and twist increasing stage: chirality reversed to left-handed

14

Time(UT) T(m) h(Km) R(Km) L_av(Km) h/R h/L3:23~4:55 86 1858 526 1322 3.53 1.414:57~5:48 74 1598 478 1322 3.34 1.216:04~6:48 42 907 359 1322 2.52 0.69

h/R and h/L: on shrinking and twist increasing stage

3:23~6:48 UT Dec 11(h/R) >1.63, the chirality of the filament remains the same.

This is consistent with the theory of Ryutova et al. 2008.

The decreasing trend of h/R reveals the twisting motion of the punumbra filament.

The decreasing trend of h/L imply that, along with the twisting motion, the instability increase.

15

4. Screw pinch instability and a C2.6 flare

Safety factor: h/L<1 (ratio of pintch to length) instability (Ryutova et al. 2008)

Taking the distance between two nearby bright point in the G-band images as the estimated screw pitch:From 04:23UT to 5:07 UT of Dec. 11h_estimate=1754~1036 Km and L~1322Km, h/L=1.33~0.78, a C2.6 flare occurred at 05:13 UT.

At 5:07 UT Dec 11Safty factor h/L=0.78<1

11-DEC, 05:08- -05:17-- 05:23, C2.6

Probably the flare is triggered by the turning on of the screw pitch instability

Initial bright point is located at the PIL region of the penumbral filament

Sumarry• The temporal development and the changes of

punumbral filament chirality can be studied quantitatively through the screw pitch instability, h/R, h/L, which is consistent with the theory of Ryutova et al. 2008.

• The decreasing/increasing trend of h/R reveals the twisting/unwinding motion of the punumbra filament.

• The decreasing/increasing trend of h/L imply that, along with the twisting/unwinding motion, the instability increase/decrease.

• The screw pitch instability may probably responsible for the onset of the C2.6 flare.

17

18

Thanks!