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Formation of a quadrupolar-like configuration at the photosphere via emergence of W-loop. In the left movie inner and outer field lines of a flux tube are drawn in blue and red, respectively. The inner field lines form a flux rope while the outer field lines form an Ω-shaped arcade above a flux rope and W-shaped underlying loop below a flux rope. In the right movie red arrows show transverse component of photospheric magnetic field while a gray-scale map indicates the distribution of vertical magnetic flux at the photosphere. A PIL rotates as the emergence of W-loop proceeds.
This paper reports a characteristic motion of a polarity inversion line (PIL) formed at the solar surface, which is newly found by performing a three-dimensional magnetohydrodynamic simulation of flux emergence in the Sun. A magnetic flux tube composed of twisted field lines is assumed to emerge below the surface, forming a bipolar region with a PIL at the surface. A key finding is the successive half-turn rotation of the PIL, leading to the formation of a quadrupolar-like region at the surface and a magnetic configuration in the corona; this configuration is reminiscent of, but essentially different from the so-called inverse-polarity configuration of a filament magnetic field. We discuss a physical mechanism for producing the half-turn rotation of a PIL, which gives new insights into the magnetic structure formed via flux emergence. This presents a reasonable explanation of the configuration of a filament magnetic field suggested by observations.Magara, T. etal 2011 JKAS, 44, 143
