In Figure 5, the AMPERE-derived potentials from 19-22 UT are overlaid on TEC data from the MIDAS GPS-based tomographic imaging algorithm. The results indicate that our derived potential patterns are consistent with the independent TEC data. The tongue of ionization emanating from the US sector propagates directly along the path predicted by the potential contours (ion drifts are oriented along the contour lines, pointing from day to night in the center of the pattern). At other times (not shown), when Kp was lower, the potential is far smaller in magnitude and no such tongues of ionization are seen. The level of agreement between these two independent observational sets is remarkable, with azimuthal deviations in the tongue of ionization matched by variations in the dayside potential (e.g. at 22 UT).