Left panel: geometry of the cubed-sphere grid. The number of cells has been reduced compared to grids used in the other two panels to ease the identification of individual cells and their shapes. Middle and right panel: shell convection in a setup comparable to that in Sect. 5.3 but with a shallower stratification and ideal gas EoS. Middle panel: color coded Mach number in a run without well-balancing. Numerical discretization errors quickly lead to spurious flows in the central region and the maximum Mach number reaches 3 × 10⁻². In the run with deviation well-balancing shown in the right panel the convective shell is clearly maintained. The maximum Mach number is 2 × 10⁻³.