Fig. 36

Magnetic structures in a CH. The gray-coding shows the field strength in the photosphere. The black line gives roughly the boundary of the CH. The field of view for SUMER is marked as a red rectangle in both panels. The magnetic field was constructed from a MDI magnetogram. Left figure: mostly closed loops at various scales. Only closed magnetic field lines with B ≥ 30 G are shown. Right figure: only open fields with large photospheric values, B ≥ 100 G. The open flux is bundled in narrow uniform filaments and originates in stronger fields concentrated at small-scale footpoints. The flux tubes expand as they extend into the corona. Taken from Wiegelmann, Xia and Marsch (2005)