Merging and Fragmentation in Solar Active Region 10930 Caused by Emerging Magnetic Flux Tube with Asymmetric Field-Line Twist Distribution along Its Axis
In order to clarify origins of merging and fragmentation of photospheric magnetic polarity regions (MPRs) in Active Region 10930, which were associated with the formation of sigmoidal structure followed by a flare in a corona, we constructed a magnetohydrodynamic model of the AR based on flux emergence. A key feature of this model is that field-line twist was asymmetrically distributed along the axis of an emerging flux tube. While emerging below a solar surface (photosphere), weakly twisted part of the flux tube was subjected to partial splitting, producing divided MPRs in the photosphere. As the flux emergence proceeded, these divided MPRs started to merge and then broke up, while in the corona a flux rope and sigmoidal structure were formed. When the flux rope erupted, a current layer appeared below the erupting flux rope, where magnetic field locally had a deep V-shaped configuration reminiscent of a nearly anti-parallel magnetic field configuration. We discussed possible physical processes involved in characteristic evolution of MPRs that leads to forming the magnetic structure of a major sunspot surrounded by small sunspots (satellite MPRs).
Reference
Magara, T.
Journal of the Korean Astronomical Society, 52, 89
movie
movie (Yellow arrow represents photospheric sound speed.)
movie (Yellow layer represents the photosphere, while gray layer corresponds to the bottom of the corona. Yellow arrow represents 10 × photospheric sound speed.)
Yellow layer represents the photosphere, while gray layer corresponds to the bottom of the corona.
