Stratified ICM atmosphere. The density ρ₀ (in g/cm³, left); temperature T₀ (in keV, centre); and entropy S₀ (right) profiles are shown. In blue: Initial profiles common to all simulations. In yellow: Same profiles but averaged over time for the 3D run F0 with κ_eff = 0.075. In green: Same but for the 2D run S0 with a realistic Spitzer conduction (see discussion in Sect. 4.3). In red: ICM atmosphere at both hydrostatic and thermal equilibria in the presence of a hypothetical background heat flux with a Spitzer conductivity, Eq. (13), subject to the same boundary conditions on the temperature (for comparison only).