Grey shaded area: distribution of temperature versus gas pressure in two representative snapshots of metal-poor red giant surface convection simulations at  [Fe/H]  =  −3 (left panel) and  [Fe/H]  =  −2 (right panel). The simulations were computed with the radiative transfer solver for the coherent scattering case. Darker shades indicate higher frequency of occurrence. Dashed lines: mean stratifications, averaged over time and surfaces of constant Rosseland optical depth. Thin grey lines: contours of constant entropy.