Hαμ = 1 four-panel diagram at t = 102 s in the pixel indicated with a white circle in Fig. 4. The quantities, plotted as functions of frequency and altitude, are indicated in the upper left corner of each subplot and are plotted in grayscale. z = 0 Mm marks the photosphere. In all panels, the vertical velocity is shown as a function of altitude (white dotted line), where upwards velocity is positive and downwards is negative. In the upper left panel, v_z = 0 is indicated by a vertical solid white line. Additionally, the altitude where τ = 1 is also plotted in all subplots (orange dotted line). The different quantities are as follows. Upper left: opacity χ_ν over optical depth τ_ν. Upper right: total source function S_ν (Eq. (2)), temperature (green line) and source function (blue line). Lower left: attenuation factor τ_νexp(−τ_ν). Lower right: contribution function C_I (Eq. (3)), and emergent intensity (solid white line).