We performed a three-dimensional MHD simulation for reproducing emergence of a twisted flux tube
in an undulated shape, to investigate subsurface origins of several observed
features of a solar filament. These features are found in fine structure with barbs and satellite/parasitic polarity regions and flux cancellation proceeding below the filament. We found that the emergence of the undulated flux tube with left-handed (right-handed) field-line twist may provide a natural formation process of a dextral (sinistral) filament (Magara 2007a; see also the bottom panel in the figure given below). We also found that emergence of shallow U-loops composing the lower half of the flux tube produced flux cancellation in a solar surface where opposite magnetic polarity regions apparently converged to a polarity inversion line between them, while a diverging plasma flow was generated on these U-loops (Magara 2007b).
References
Magara, T.
2007a PASJ, 59, L51
Magara, T.
2007b ASPC, 369, 809
Magnetic structure of solar filament formed via emergence of undulated flux tube with left-handed field-line twist. Upper panel shows pre-emergent (t=5) and post-emerged (t=33) states of the flux tube. Outer and inner field lines of the flux tube were drawn in red and white, respectively. Lower panel shows spatial relationship between the main and satellite/parasitic polarity regions rooted by the inner (dark blue) and outer (green and orange) field lines, respectively. The inner and outer field lines compose magnetic structure of the main body (spine) and feet (barbs) of the filament, respectively. From Magara (2007a).