Growth of magnetic energy with time and kinetic and magnetic spectra. Left: temporal profiles of the magnetic energy density averaged over the full domain as function of time for simulations dh24, dh16, dh12, dh8, dh6, dh6ν_sη_H25, and dh6η_H12. Solid lines denote simulations showing dynamo action, whereas dashed lines denote simulations without dynamo action. Right: spectra of the normalised kinetic energy density (solid lines) and magnetic energy density (dashed lines) averaged over the time span of the kinematic phase and in space between z = −900 km and z = −700 km.