Dipped magnetic field configurations associated with filaments and barbs

In this paper, three-dimensional linear force-free field configurations tha t can be associated with filaments are considered. It is assumed that the f ield configurations are suitable to represent filaments if they contain mag netic dips. With the photospheric Bur distribution chosen to be an arcade w ith a dextral/sinistral axial component, it is found that dipped configurat ions exist only for large values of alpha (where, del x B = alpha B). The d ips always lie above the polarity inversion line in the centre of the chann el between the flux regions. When the dips are viewed from above to a depth of 1 Mm they resemble closely the shape of filaments viewed in absorption on the solar disk. As the magnitude of alpha increases, the horizontal acid vertical extent of the dips also increases, giving active-region filaments for low values of alpha and quiescient filaments for high values of alpha. Dextral filaments only form for negative values of alpha and sinistral fil aments for positive values of alpha. The portion of the field line that is dipped is always of inverse polarity and the magnitude of the field in the dipped region increases with height, both of which are consistent with Lero y, Bommier, and Sahal-Brechot (1983). Overlying the region of dips there ar e arcades of normal polarity which have the correct left-bearing/right-bear ing orientation for dextral/sinistral filaments. When the hypothesis of bar bs occurring in dipped field lines is used, barbs that branch out of the ma in axis and to the right/left for dextral/sinistral filaments can be formed around minority polarity elements on either side of the polarity inversion line. No barbs are found around normal polarity elements. The model reprod uces many of the observed features of filament channels, filaments and thei r barbs.