Vertical (left) and horizontal (right) velocity maps in a typical 3D snapshot of the red giant model constructed at different geometrical depth, z, with z = 0 set at log τ_Ross = 0 and increasing towards the stellar center. Locations where the vertical velocity  Mach (supersonic down-flows) are marked with white contours, those where v_z and v_h exceed 1 Mach are contoured in black (contours start at Mach =  ± 1.0 and are drawn at every  ± 0.5 Mach thereof). Vertical lines mark the x position (x = 7.77 × 10¹¹ cm) at which the 1D velocity profiles shown in Fig. 8 were taken.