Magnetic Shear in Two-ribbon Solar Flares

Magnetic Shear in Two-ribbon Solar Flares Yingna Su1,2 Advisors: Leon Golub1, Guangli Huang2 Collaborators: A. A. Van Ballegooijen1, E. E. Deluca1, J. McCaughey1, K. K. Reeves1, and M. Gros3 1.Harvard-Smithsonian Center for Astrophysics, USA 2. Purple Mountain Observatory, China 3. DSM/DAPNIA/Service d’Astrophysique, CEA Saclay, France 2007 SPD dissertation talk, Honolulu, 05/28/2007

Acknowledgements • Advisors:Leon Golub (CfA), Guangli Huang (PMO) • Collaborators:A. A. Van Ballegooijen, E. E. Deluca, J. McCaughey, K. K. Reeves, and M. Gros • Valuable suggestions fromS. K. Antiochos, J. Lin, J. Karpen, B. Schmieder… • Other CfA SSXG group members:M. Weber, J. Cirtain, M. Bobra, P. J. Jibben, S. Saar, K. Korreck, A. Savcheva, L. Lundquist, and J. Bookbinder • Instruments:TRACE, Hinode/XRT, SOHO/MDI, SOHO/LASCO, SOHO/EIT, NJIT/BBSO, SPI/ACS, Hinode/SOT, RHESSI • Financial support:TRACE contract from Lockheed Martin and NASA contract NNM07AA02C at CfA

Outline • Background (Su et al. 2006, solar physics, 236, 325) • Statistical Analysis of Shear Motion (Su et al. 2007a, ApJ, 655, 606) • What Determines the Intensity of Solar Flare/CME events? (Su et al. 2007b, ApJ, 665, 1448) • Conclusions • Preliminary results from Hinode/XRT --Evolution of the sheared magnetic fields in AR10930 (Su et al. 2007c, PASJ, submitted)

Shear Motion of Footpoints • EUV brighteningpairs Start:close to the magnetic inversion line (MIL), but widely separated along the MIL (Fig. a, highly sheared) End:straight across and far from the MIL (Fig. f, weakly sheared) • Strong-to-weak shear motion of the footpoints • Hard X-ray observations (Yohkoh/HXT)(Masuda, Kosugi, and Hudson 2001) • Hα, EUV, and microwave observations (Su et al. 2006 and references therein)

Interpretation Cartoon of the evolution of the magnetic field in the standard model of solar flares( Su et al. 2006). This observed shear change can be understood by the cartoon we made corresponding to the standard model for solar flares. (e.g., Moore et al. 2001 and references therein).

Motivation • Two Questions: • Is the shear motion of the footpoints common? • Could the change from the impulsive to gradual phase be related to the magnetic shear change?(Lynch et al. 2004)

Distribution of Shear Angles Data sample: 50 two-ribbon flares well observed by TRACE • Type I flares: 86%(43 out of 50) • Ribbon separation: Yes • Shear motion: Yes • For 24 Type I flares • Initial shear angles: 50°– 80° • Final shear angles: 15°– 55° • Change of shear angles: 10°– 60°

Distribution of TEIP - TCSM • 15 Type I flares • measured shear angle • corresponding HXR observations • TEIP - TCSM: 0~2 min In most events, the cessation of shear change is 0-2 minutes earlier than the end of the impulsive phase.

Data sets and methods • Data sample: 18 Type I flares • associated with CMEs • measured shear angles • Six magnetic parameters: • Parameters representing magnetic size: Background field strength (B), the area (S), and magnetic flux (F) • Parameters representing magnetic shear: Initial shear angle (q1), final shear angle (q2), and change of shear angle(q12) • Intensity of flare/CME events: Peak flare flux (PFF) and CME speed (VCME)

Result I • log10B, log10S,log10Fvs. log10(PFF), VCME : positive correlations • log10Fis better than log10B, log10S (F =B×S)

q1vs.log10(PFF), VCME : no correlation • q2 , q12vs.log10(PFF), VCME : negative and positive correlations Result II • q12is better than both q1 and q2 (q12 = q1- q2 )

Result III • Three multi-parameter combinations vs. log10(PFF) and VCME : strong linear correlations • Combination 2 (log10F , q1 , q12 ) is the top-ranked combination • Combination 2 is only slightly better than combination 3 (log10F , q12)

Conclusions • The strong-to-weak shear motion of the footpoints is a common feature in two-ribbon flares. • The cessation of magnetic shear change is 0-2 minutes earlier than the end of the impulsive phase in 10 out of the 15 events,which suggests that the change from impulsive phase to gradual phase is related to the magnetic shear change. • The magnetic flux and change of shear angle are two best parameters which show comparably strong correlations with the peak flare flux and CME speed. A multi-parameter combination shows better correlation than individual parameter. • The intensity of solar flare/CME events may depend mainly on the released magnetic free energy (q12) rather than the total magnetic free energy (q1) stored prior to the eruption.

Observational Data • Target: NOAA AR 10930 where two X-class flares occurred: • X3.4 flare on 2006/Dec/13 • X1.5 flare on 2006/Dec/14 • Data from: • Hinode/XRT • Hinode/SOT • TRACE • SOHO/MDI • Topic: Evolution of the sheared core field prior to, during, and after the flares.

Formation of the sheared core field XRT observations of sheared field formation: From 00:19 UT on Dec 10 To 12:43 UT on Dec 12 • SOT observations of • Emerging flux • West-to-east Motion • CCW Rotation • in the Lower sunspot

Part of the sheared cored field erupted, while part of them stayed behind. X 3.4 flare on 2006/12/13 X1.5 flare on 2006/12/14

Pre-flare vs. post-flare sheared core field (Dec 13 flare) • Post-flare core field is less sheared than the pre-flare core field • Reformation or partial eruption of the filament

Pre-flare vs. post-flare sheared core field (Dec 14 flare) • Post-flare core field is less sheared than the pre-flare core field • Reformation or partial eruption of the filament

Summary • The formation of the sheared core field is caused by the CCW rotation and west-to-east motion of an emerging sunspot. • XRT observations of partial eruption of the sheared core field may explain the existence of the filament after the flare. • Post-flare core field is much less sheared than the pre-flare core field, which is consistent with the scenario that the energy released during the flare is stored in the highly sheared core field.

Thank you for your attention !

Part of the sheared cored fields erupted, Part of the sheared core fields stayed behind

Magnetic Shear in Two-ribbon Solar Flares