Prominences (called filaments when they are observed on the solar disk) often lie along polarity inversion lines (PILs - lines separating positive and negative polarity regions). A well-known feature of the corona is that a large-scale shear and twist of the magnetic field is often present at these locations (referred to as filament channels). This energization of the magnetic field can structurally change the shape and morphology of the overlying streamers. Our procedure for energizing the field is described in our paper about the 2017 Eclipse prediction. For this preliminary prediction, the handedness of the shear was estimated using the hemispheric rule in quiet sun, and by visual inspection of AIA images for active regions. The introduction of shear qualitatively changes the shape of the streamers and the connectivity of the underlying fields, and increases the free magnetic energy in the corona.
The PIL segments where we emerged shear and twist are illustrated on the two maps below. The PIL segments (thick colored lines) were selected by examining H-alpha and AIA observations for evidence of filamentary structures, starting from about 45 days before the prediction.