  A magnetic channel - a series of polarity reversals separating elongated flux
threads with opposite polarities - may be a manifestation of a highly
non-potential magnetic configuration in active regions. To understand its
formation we have carried out a detailed analysis of the magnetic channel in AR
10930 using data taken by the Solar Optical Telescope/Hinode. As a result, we
found upflows (-0.5 to -1.0 km/s) and downflows (+1.5 to +2.0 km/s) inside and
at both tips of the thread respectively, and a pair of strong vertical currents
of opposite polarity along the channel. Moreover, our analysis of the nonlinear
force-free fields constructed from the photospheric magnetic field indicates
that the current density in the lower corona may have gradually increased as a
result of the continuous emergence of the highly sheared flux along the
channel. With these results, we suggest that the magnetic channel originates
from the emergence of the twisted flux tube that has formed below the surface
before the emergence.
