The magnetic structure of solar prominence cavities: New observational signature revealed by coronal magnetometry

The Coronal Multi-Channel Polarimeter (CoMP) obtains daily full-Sun above-the-limb coronal observations in linear polarization, allowing, for the first time, a diagnostic of the coronal magnetic field direction in quiescent prominence cavities. We find that these cavities consistently possess a characteristic "lagomorphic" signature in linear polarization indicating twist or shear extending up into the cavity above the neutral line. We demonstrate that such a signature may be explained by a magnetic flux-rope model, a topology with implications for solar eruptions. We find corroborating evidence for a flux-rope structure in the pattern of concentric rings within cavities seen in CoMP line-of-sight velocity.