Half-turn rotation of polarity inversion line associated with formation of quadrupolar-like structure via flux emergence
We performed a three-dimensional MHD simulation of an emerging twisted flux tube to investigate what causes half-turn rotation of a neutral line/polarity inversion line (PIL) in a solar surface. When it emerged, the flux tube first produced a bipolar region with the PIL in the surface, followed by the half-turn rotation of the PIL associated with formation of quadrupolar-like structure. The magnetic field configuration is given by W-shaped field lines (W-loops), which is reminiscent of, but essentially different from the so-called inverse-polarity configuration proposed for magnetic structure of a solar filament/prominence. We demonstrated that W-loop emergence is the underlying physical process responsible for the formation of quadrupolar-like structure and the half-turn rotation of the PIL. The W-loop emergence may play a key role in stabilizing the magnetic structure of the filament/prominence.
Reference
Magara, T. et al. 2011 JKAS, 44, 143
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Formation of quadrupolar-like structure and half-turn rotation of PIL via W-loop emergence. In the left movie inner and outer field lines of emerging flux tube are drawn in blue and red, respectively. The inner field lines compose flux rope, while the outer field lines are regarded as Ω-loops overlying the flux rope and W-loops underlying the flux rope (see also pre-eruptive magnetic structure). In the right movie red arrows represent transverse component of surface magnetic field, while the gray-scale map shows distribution of vertical magnetic flux density in the surface.
