Three-dimensional view of magnetic field lines. Left panels: extrapolated field lines computed using the observed photospheric magnetic field as a lower boundary condition (top panel: lateral view, bottom panel: top view). The B_z component of the magnetic field strength is shown in the background. Right panels: extrapolated field lines computed using the observed chromospheric magnetic field as a lower boundary condition (top panel: lateral view, bottom panel: top view). The intensity image in the background shows He absorption features along the loops; closed black and white contours represent the locations of photospheric positive and negative polarity, respectively.