We performed a three-dimensional MHD simulation in which a twisted flux tube emerges
in an undulated shape (undulated flux tube), to investigate subsurface origins of the following observed
features of a solar filament: barbs and satellite/parasitic polarity regions and flux cancellation proceeding below the filament. The simulation showed that an undulated flux tube of left-handed (right-handed) field-line twist naturally formed a dextral (sinistral) filament (Magara 2007a). The simulation also showed that emergence of shallow U-loops composing lower half of the twisted flux tube produced flux cancellation in a solar surface where opposite magnetic polarity regions apparently converge to a polarity inversion line between them, while on these U-loops a diverging plasma flow arises (Magara 2007b).
References
Magara, T.
2007a PASJ, 59, L51
Magara, T.
2007b ASPC, 369, 809
Magnetic structure of solar filament formed dynamically via emergence of undulated flux tube of 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 are drawn in red and white, respectively. Lower panel shows spatial relationship between the main and satellite/parasitic polarity regions, which are rooted by the inner (dark blue) and outer (green and orange) field lines, respectively. The inner and outer field lines compose magnetic structure of main body (spine) and feet (barbs) of the filament, respectively. From Magara (2007a).