  Solar magnetic fields comprise an 11-year activity cycle, represented by the
number of sunspots. The maintenance of such a solar magnetic field can be
attributed to fluid motion in the convection zone, i.e. a dynamo. This study
conducts the mean-field analyses of the global solar dynamo simulation
presented by Hotta et al. (2016). Although the study succeeds in producing
coherent large-scale magnetic fields at high Reynolds numbers, the detailed
physics of the maintenance of this field have not been fully understood. This
study extracts the alpha-tensor and the turbulent magnetic diffusivity tensor
through mean-field analyses. The turbulent magnetic diffusivity exhibits a
significant decrease towards high Reynolds numbers. The decrease in the
turbulent magnetic diffusivity suppresses the energy conversion of large-scale
field to small-scale field. This implies that the decrease in the turbulent
magnetic diffusivity contributes to the maintenance of a large-scale magnetic
field at high Reynolds numbers. A significant downward turbulent pumping is
observed; it is enhanced in the weak phase of the large-scale field. This study
proposes a cyclic reversal process of a large-scale field which is dominantly
driven by the alpha-effect and is possibly triggered by downward pumping.
