Comparison of footpoint locations for PFSS extrapolations using different values of ℓ_max (left), R_ss (middle), and SSW synchronic map dates (right). The STEREO-A/EUVI 304 Å image of the brightening on December 16 at 04:36 UT is also shown, with the brightening location marked by the white arrow. In the right panel, although the date of the input synchronic map differs from the time of the event, each field line footpoint is projected at the correct Carrington coordinates during the brightening.