FINE-STRUCTURE OF SOLAR FILAMENTS .2. DYNAMICS OF THREADS AND FOOTPOINTS

A filament observed in an active region in June 1986 underwent a slow Disparition Brusque which lasted 4 d. Here we focus our study on the dynamical behaviour of the fine structures (scale approximately 350 km) in this filament. The fine structures were observed at the Pic du Midi with the Multi-Channel Subtractive Double Pass (MSDP) spectrograph during a period of 15 min. We observed no substantial changes in intensity during this period. However, we observed widespread continual changes in the velocity field and, for the region taken as a whole, there was virtually no correlation from one minute to the next. High velocities (up to +/- 15 km s-1) were detected using the first order differential cloud model method at the locations where the filament was anchored in the chromosphere. We argue that these footpoints are essentially the same kind of structures as the chromospheric bushes seen around supergranules, showing spicule-like activity modified by the local magnetic field geometry, and which may supply matter to the filament by direct injection. Elongated Doppler structures with coherent motions were observed parallel to the filament axis. These structures may be interpreted as magnetic flux tubes identifiable during their short rise time, or they may indicate the presence of coherent wave motions.