Mean latitudinal profile of the Nusselt number defined in Eq. (3), for models with N_ρ = 3, E = 3 × 10⁻⁵, and Pr = 1. The value of the Rayleigh number Ra increases from the left to the right and the magnetic Prandtl number Pm is varied. Solid black lines represent either pure hydrodynamic models or MHD models without magnetic dynamo (i.e., too low values of Pm). Note that panel (a) is similar to Fig. 6a but is added here for the sake of completeness and comparison.