Twist Accumulation and Topology Structure of a Solar Magnetic Flux Rope

Abstract

To study the build up of a magnetic flux rope before a major flare and coronal mass ejection (CME), we compute the magnetic helicity injection, twist accumulation, and the topology structure of the three dimensional 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 40 Mx 2 hr −1 . We find that only about 1.8% of the injected magnetic helicity became finally the internal helicity of the magnetic flux rope, whose twist increasing rate was −0.18 ± 0.08 Turns hr −1 . The quasiseparatrix layers (QSLs) of the three dimensional 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.

Tracking the Evolution of a Coherent Magnetic Flux Rope Continuously From the Inner to the Outer Corona

“…DEM analysis shows that the MFR top and footpoints were heated to over 6.0 MK. It is hypothesized that the heating may result from the reconnection near the periphery of the MFR, i.e., QSLs, where the magnetic linkages undergo drastic changes and, hence, strong current layers are formed there (Demoulin et al 1996;Savcheva et al 2012b;Guo et al 2013). The reconnection in the presumed QSLs has two important roles in the slow rise phase.…”

Magnetic reconnection during eruptive magnetic flux ropes

“…1, which is calculated by sampling points on the z-axis. These Φ num values are calculated by the integration of the angular variation along the magnetic axis curve of MFR (Guo et al 2013). Its value on the MFR surface is about five turns, which means the MFR is kink unstable.…”

FORCED FIELD EXTRAPOLATION OF THE MAGNETIC STRUCTURE OF THE Hα FIBRILS IN THE SOLAR CHROMOSPHERE

“…Preprocessing the magnetogram has been very popular Schrijver et al 2008;De Rosa et al 2009;Tadesse et al 2009;Guo et al 2013;Cheng et al 2014;Jiang et al 2014;Wang et al 2015), which makes it more consistent with NLFFF. Metcalf et al (2008) showed that preprocessing improved the metrics quantifying the agreement between the NLFFF solution and reference model field.…”