Divergence of the plasma velocity field, ∇ ⋅ u, for Experiments 1 (top) and 2 (bottom) at different stages of the magnetic flux emergence process. Arrows are superimposed pointing out the location of some of the shocks within the emerged regions. Dashed lines indicate the location of the solar surface (line at z = 0 Mm) and of the transition region (isocontour at T = 10⁵ K). An animation of this figure is available online.