High-resolution images obtained in Hα with the new Swedish Solar Telescope at La Palma, Spain, have been used for studies of fine-scale threads in solar filaments. The widths of the thin threads are ≤0.3 arc sec. The fact that the width of the thinnest threads is comparable to the diffraction limit of the telescope of about 0.14 arc sec, at the wavelength of Hα, suggests that even thinner threads may exist. Assuming that the threads represent thin magnetic strings, we conclude that only a small fraction of these are filled with observable absorbing plasma, at a given time. The absorbing plasma is continuously flowing along the thread structures at velocities 15 ± 10 km s −1 , which suggests that the flows must be field-aligned. In one case where a bundle of thin threads appears to be rooted in the nearby photosphere, we find that the individual threads connects with intergranular, dark lanes in the photosphere. We do not find signs of typical network fields at the 'roots' of the fine threads, as normally evidenced by bright points in associated G-band images. It is suggested that filament threads are rooted in relatively weak magnetic fields.

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The locations of barbs of quiescent solar filaments are compared with the photospheric/chromospheric network, which thereby serves as a proxy of regions with enhanced concentrations of magnetic flux. The study covers quiet regions, where also the photospheric network as represented by flow converging regions, i.e., supergranular cell boundaries, contain largely weak magnetic fields. It is shown that close to 65% of the observed end points of barbs falls within the network boundaries. The remaining fraction points into the inner areas of the network cells. This confirms earlier findings (Lin et al., Solar Physics, 2004) that quiescent filaments are basically connected with weaker magnetic fields in the photosphere below.

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Post-flare loops were observed on June 26, 1992 in the Ho~ line with the Multichannel Subtractive Double-Pass spectrograph (MSDP) on Pic-du-Midi and with the Swedish telescope on La Palma. The highly dynamic loops are inhomogeneous (blobs). The cool loops were observed 10-12 hours after the X 3.9 class flare which had a maximum on June 25 at 20:11 UT. From 2D images obtained with the MSDP on June 26 we derive Ho~ intensities and Doppler velocities of the loop plasma. Using a geometrical reconstruction technique we show that these loops are mainly perpendicular to the solar surface and have the shape of a dipole magnetic configuration. We derive the bulk-flow velocities along the loop as a function of height using the Doppler velocities and the results from the loop reconstruction. Where the Doppler velocities are too small, we derive the bulk-flow velocities from the displacements of the falling blobs. We discuss existing deviations from free-fall velocity in the lower parts of the loops.