Prominence magnetic dips in three-dimensional sheared arcades

We calculate the distribution of field-line dips in the three-dimensional sheared arcade model for prominence/filament magnetic fields. We consider both moderately and highly sheared configurations computed by fully time-dependent three-dimensional MHD simulations in which the field was relaxed to a static equilibrium end state. In agreement with previous low spatial resolution measurements of the magnetic field inside prominences, we find that for all configurations, the field in the great majority of the calculated dips exhibits inverse polarity. But for each configuration we also find well-defined narrow regions with stable dips of normal polarity. These tend to be located on the edges of the filament ends and at the top of the central part of the prominence. This distinctive mixture of normal/inverse polarity dips that we find in sheared arcades is not likely to be present in twisted flux rope prominence models. Therefore, our results provide a rigorous and unique observational test that can distinguish between the two classes of models, as well as new predictions for future high spatial resolution spectropolarimetric observations of filaments and prominences.