Initial set-up of the flux emergence MHD simulation. Top: Dependence on height of the initial values of density, temperature, gas, and magnetic pressure (in cgs units). The vertical line denotes the location of the photosphere. Bottom: Initial configuration of the magnetic field, consisting of the twisted flux tube (black field lines) and the uniform, oblique ambient field (white field lines). The density stratification is shown with colour in the background, on a logarithmic scale. The yellow boxes are the projections of the subvolumes examined in Sect. 4.2 on the respective planes.