HR: 16:00h
AN: SH54B-03    [Abstracts]
TI: Magnetic Twist and Writhe of Delta Active Regions
AU: * Tian, L
EM: alicetlr@rice.edu
AF: Department of physics and astronomy, Rice University, 6100 Main Street, Houston, TX 77005 United States
AU: Alexander, D
EM: dalex@rice.edu
AF: Department of physics and astronomy, Rice University, 6100 Main Street, Houston, TX 77005 United States
AU: Liu, Y
EM: yliu@quake.stanford.edu
AF: W. W. Hansen Experimental Physics Lab., Stanford University, Stanford, San Francisco, CA 94305-4085 United States
AU: Yang, J
AF: Beijing Normal University, Haidian District, Beijing, 100875 China
AB: Active regions with a δ magnetic configuration from 1996 to 2002 were selected to study how important a role the kink instability plays in such active regions. We employ the systematic tilt angle of each active region as a proxy for the writhe of a fluxtube and the force-free parameter, α_best, as a proxy for the magnetic field twist in the fluxtube. It is found that 65-67% of the 104 active regions have the same sign of twist and writhe, which violate the Hale-Nicholson and Joy's Laws (HNJL) or the hemispheric helicity rule (HHR). 68% (46/68) of these active regions produced more than five large flares. Active regions violating HNJL, but following HHR, have a much stronger tendency to produce X-class flares and/or strong proton events. Continuously clockwise rotation of magnetic configuration of a long-lived active region (AR 9604-9632-9672-9704-9738) which produced major flares, fast CMEs and many strong proton events shows that a kink instability would play very important role in such active regions. These results support the prediction for the presence of a kink instability, that the twist and writhe of the magnetic fields exhibit the same sign for δ active regions (Linton et al, 1998, 1999, and Fan et al., 1999). Finally, we analyze possible origins of the twist and writhe of the magnetic fields for the active regions with different relations between the twist and writhe.
DE: 7513 Coronal mass ejections
DE: 7519 Flares
DE: 7524 Magnetic fields
DE: 7529 Photosphere
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2005 Joint Assembly