Authors: Bruce W. Lites
Affiliation: National Center for Atmospheric Research, High Altitude Observatory
The Advanced Stokes Polarimeter has been used to simultaneously measure the photospheric vector magnetic field (Fe I 630 nm) and chromospheric structure (Ha) in a number of active regions. These data have been examined for the possible occurrence of low-lying filaments which might be associated with flux ropes at the photospheric level. Presented here are high-resolution measurements of the photospheric vector magnetic field that suggest such occurrence is not at all uncommon. I examine regions where 1) the active region vertical magnetic field component has a significant length of contiguous opposite polarities (a ``polarity inversion line''), that is 2) accompanied by a filament observed in Ha along this polarity inversion line, 3) that occurs in plage and not in sunspots or large pores, and 4) is not accompanied by an Ha arch filament system running perpendicular to the polarity inversion line. In nearly every case examined, the horizontal photospheric field vector is aligned along the length of the polarity inversion line, in agreement with the widely-accepted flux rope picture of the overlying chromospheric filament. In several cases the photospheric vector field takes on the character of a ``concave-upward' geometry in the immediate vicinity of the inversion line. This finding suggests that the flux ropes that support active region prominences are generated in the solar interior and rise through the photosphere into the corona to form filaments.