Departures from statistical equilibrium from a vertical slice through the Bifrost simulation. Top panel: departure of the total source function from SE. Middle panel: departure of the hydrogen n = 2 populations from SE. Bottom panel: temperature structure of the Bifrost simulation. The vertical slice is taken at the position marked with white dashed lines in Fig. 6. Red solid: Hετ = 1 height for SE. White dashed: Hετ = 1 height for HNEI.