Mean latitudinal profile of the surface Nusselt number defined in Eq. (3), for three typical models. (a) E = 3 × 10⁻⁵, Pr = 1, N_ρ = 3, and Ra ≈ 1.7 Ra_c close to the onset of convection (b) E = 3 × 10⁻⁵, Pr = 0.3, N_ρ = 4, and Ra ≈ 3 Ra_c at the transition toward turbulent flows (c) E = 3 × 10⁻⁴, Pr = 1, N_ρ = 6, and Ra ≈ 8 Ra_c. Left: variations with the magnetic Prandtl number Pm. Solid black lines represent either pure hydrodynamic models or MHD models without magnetic dynamo (i.e., too low values of Pm). Right: spherical representation for the nonmagnetized model (i.e., the lowest value of Pm) and the most magnetized dynamo model (i.e., the highest value of Pm) in each case. Note that we use different colorbars in each row to enhance the visualization contrast.