Mass density in a vertical cut through the model atmosphere along the blue line in Fig. 8. For each spectral line mentioned in the legend, corresponding dashed curves show the maximum formation height at optical depth unity. The white dotted line shows the first occurrence from the upper convection zone where the magnetic pressure equals gas pressure (β = 1). The arrows show the direction of the magnetic field vector in the plane of the cut along the formation height curve of Hα. These arrows are plotted every tenth grid point.