On arch-filament systems in spotgroups

Systems of arch-shaped filaments (AFS) occurring in the interspot region of young bipolar groups are studied. Their main characteristics are: Average length: 30000km, average width 20000km, width of individual filaments 1000–3000 km, height of arches 4–15000 km. A typical lifetime of the filaments 30 min; appreciable changes of the system occur within several hours; the lifetime of a system is about three days. - The arch-filament systems bridge the neutral line and connect the regions of the innermost spots of opposite polarity. Material moves along the filaments (v 25–50 km/sec) following the direction of the magnetic field, and sometimes arches are observed rising at a rate of 20 km/sec. They are very dark on the inner disk and appear either in emission or in absorption close to the solar limb. - The occurrence of bright points (moustaches) is found to be closely associated with AFS in young spotgroups. - The possible nature of AFS and their relation to other types of filamentary structures is discussed.