Average relative density for each radial velocity at different radii for the O4 model. 〈ρ_r〉 is the average density at every radial cell. Colours here represent relative density (ρ/〈ρ_r〉) with yellow displaying under-dense regions and blue representing over-dense clumps. The red dash-dotted line indicates the local escape velocity, the black dashed vertical line is the average photosphere 〈R_★〉 and the black dash-dotted vertical line is the average sonic point 〈R_sonic〉. The zoomed-in part highlights the regions below the optical photosphere.