Study of Magnetic Helicity Injec-tion in the Active Region NOAA 11158 Associated with the X-class Flare of 2011 February 15

Sung-Hong Park1, K. Cho1, Y. Kim1, S. Bong1,

D. E. Gary2, Y. Park1

1 Korea Astronomy and Space Science Institute2 New Jersey Institute of Technology

1. Aims

The main objective of this study is to examine a long-term (a few days) precondition and a trigger mechanism for an X2.2 flare peaking at 01:56 UT on 2011-Feb-15 in GOES soft X-ray flux.

For this, we investigate the variation of magnetic helicity injection through the photospheric surface of the flare-productive active region NOAA 11158 dur-ing (1) the long-term period of February 11-15 with a 1-hour cadence and (2) the short-term period of 01:26-02:10 UT on February 15 with a 45-second cadence

2. Magnetic Helicity

Magnetic helicity is a useful parameter to quanti-tatively measure the global complexity and non-po-tentiality of a magnetic field system (Démoulin & Pariat 2009).

Magnetic helicity consists of: (a) twists of mag-netic field lines inside a flux tube and kinks of flux tube axes, and (b) inter-linkages between flux tubes.

(1) Method -Helicity Flux Density (Pariat et al. 2005)

where Bn is the normal magnetic field component, x is the po-sition vector, and u is the apparent horizontal velocity of the photospheric field line footpoints. u is measured with the dif-ferential affine velocity estimator (DAVE) method developed by Schuck (2006).

3. Helicity Calculation

-Helicity Injection Rate & Helicity Accumula-tion

(2) DataThe helicity injection was determined using line-of-sight magnetograms with high spatial and temporal resolution taken by the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observa-tory (SDO).

2011-02-12 19:00 UT2011-02-11 08:00 UT 2011-02-12 08:00 UT

2011-02-13 08:00 UT 2011-02-14 08:00 UT 2011-02-15 08:00 UT

(3) Example: Velocity Map

(3) Example: Helicy Flux Density Map

(1) Long-term Profile of Helicity In-jection

4. Results

X2.2

(2) Short-term Profile of Helicity In-jection

01:48 UT Note that when the total injection rate of helicity in the flar-ing active region changed its sign from positive (right-handed) to negative (left-handed), the X2.2 flare occurred simultaneously.

(3) Helicity Injection Rate vs. KSRBL Ra-dio Flux

The Korean Solar Radio Burst Locator (KSRBL) is a radio spectrometer designed to observe solar decimeter and microwave bursts over a wide band (0.245-18 GHz).

(4) Helicity Flux Density Maps

2011-02-15 01:40:24 UT 2011-02-15 01:49:24 UT

2011-02-15 01:51:39 UT 2011-02-15 01:53:09 UT

2011-02-15 01:56:09 UT 2011-02-15 02:06:39 UT

(5) Potential Field Extrapolation

Red (Blue) lines indicate the field lines of which foot points have positive (negative) magnetic helicity.

2011-02-15 01:44:09 UT

2011-02-15 01:49:24 UT

2011-02-15 01:51:39 UT

5. Summary & Conclusions We found two characteristic phases of helicity in-jection related to the X2.2 flare.

(1)A large amount of positive helicity was first in-jected over ~2 days with a phase of monotoni-cally increasing helicity.

(2)Then the flare started simultaneously with a sig-nificant injection of the opposite (negative) sign of helicity around the flaring magnetic polarity inversion line.

Injection of he-licity of oppo-site sign

Phase 1flare

Monotonically increasing he-licity

Phase 2

This observational finding clearly supports the pre-vious studies that (1) there is a continuous injection of helicity a few days before flares (Park et al. 2008, 2010) and (2) a rapid injection of the helicity in the opposite sign into an existing helicity system trig-gers flares (Kusano et al. 2003).

Formation of helicity inver-sion layers by the injection of the countersigned helicity by shear motion and/or by emergence (Kusano et al. 2003)

ReferencesDémoulin, P., & Pariat, E. 2009, Adv. Space Res., 43, 1013Kusano, K., et al. 2003, Adv. Space Res., 32, 1931Pariat, E., et al. 2005, A&A, 439, 1191Park, S.-H., et al. 2008, ApJ, 686, 1397Park, S.-H., et al. 2010, ApJ, 718, 43Schuck, P. W. 2006, ApJ, 646, 1358

AcknowledgmentsThe authors thank the SDO/HMI team for providing the full-disk photospheric magnetogram data with high spatial and temporal resolution via the Joint Science Operations Center (JSOC).