Twist accumulation and topology structure of a solar magnetic flux rope

Journal Article · Fri Dec 20 04:00:00 EST 2013 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/779/2/157· OSTI ID:22348434

Guo, Y.; Ding, M. D.; Cheng, X. ^[1]; Zhao, J. ^[2]

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1. School of Astronomy and Space Science, Nanjing University, Nanjing 210093 (China)
2. Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 (China)

To study the buildup of a magnetic flux rope before a major flare and coronal mass ejection (CME), we compute the magnetic helicity injection, twist accumulation, and topology structure of the three-dimensional (3D) magnetic field, which is derived by the nonlinear force-free field model. The Extreme-ultraviolet Imaging Telescope on board the Solar and Heliospheric Observatory observed a series of confined flares without any CME before a major flare with a CME at 23:02 UT on 2005 January 15 in active region NOAA 10720. We derive the vector velocity at eight time points from 18:27 UT to 22:20 UT with the differential affine velocity estimator for vector magnetic fields, which were observed by the Digital Vector Magnetograph at Big Bear Solar Observatory. The injected magnetic helicity is computed with the vector magnetic and velocity fields. The helicity injection rate was (– 16.47 ± 3.52) × 10{sup 40} Mx{sup 2} hr{sup –1}. We find that only about 1.8% of the injected magnetic helicity became the internal helicity of the magnetic flux rope, whose twist increasing rate was –0.18 ± 0.08 Turns hr{sup –1}. The quasi-separatrix layers (QSLs) of the 3D magnetic field are computed by evaluating the squashing degree, Q. We find that the flux rope was wrapped by QSLs with large Q values, where the magnetic reconnection induced by the continuously injected magnetic helicity further produced the confined flares. We suggest that the flux rope was built up and heated by the magnetic reconnection in the QSLs.

• OSTI ID: 22348434
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 779; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
EXTREME ULTRAVIOLET RADIATION
HELICITY
INJECTION
LAYERS
MAGNETIC FIELDS
MAGNETIC FLUX
MAGNETIC RECONNECTION
MASS
Q-VALUE
SUN
THREE-DIMENSIONAL CALCULATIONS
VELOCITY