Fig. 4: Hε synthesized with electric fields.

a Stokes-I, b Stokes-\(Q/I\), c Stokes-\(V/I\), and d Stokes-\(U/I\) profiles in the Balmer line of neutral hydrogen, Hε, at 397.0 nm. Black curves and bars are measured data points at the location marked by the red cross in Figs. 1 and 2. Error bars are shown as the standard deviation in the continuum only for Stokes-Q/I, U/I, and V/I, because they are too small for Stokes-I. The gray curves were derived from quiet regions in the same way as the derivation of the blue dashed curve in Fig. 3d to show the Stokes signals of the weak photospheric lines. The red solid lines are profiles of Hε synthesized in the presence of an electric field and no magnetic fields. We calculated them while varying the three components of the electric field vector by 10 \({{{\rm{V}}}}\,{{{{\rm{m}}}}}^{-1}\) in strength and 5° in inclination and azimuth angles. Then, we selected some that reproduce the amplitudes of the measured profiles. The blue dashed lines are similar to that of the red lines, but with the addition of a photospheric magnetic field as inferred through the Weak Field Approximation¹² using the Fe I 630.15 nm line (Fig. 2). Source data are provided as a Source Data file.