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We perform a mean-field analysis of the EULAG-MHD millenium simulation ofglobal magnetohydrodynamical convection presented in Passos et al. 2014. Theturbulent electromotive force operating in the simulation is assumed to belinearly related to the cyclic axisymmetric mean magnetic field and its firstspatial derivatives. At every grid point in the simulation's meridional plane,this assumed relationship involves 27 independent tensorial coefficients.Expanding on Racine et al. 2011, we extract these coefficients from thesimulation data through a least-squares minimization procedure based onsingular value decomposition. The reconstructed alpha-tensor shows goodagreement with that obtained by Racine et al. 2011, who did not includederivatives of the mean-field in their fit, as well as with the alpha-tensorextracted by Augustson et al. 2015 from a distinct ASH MHD simulation. Theisotropic part of the turbulent magnetic diffusivity tensor beta is positivedefinite and reaches values of 5.0x10^7 m2s-1 in the middle of the convectingfluid layers. The spatial variations of both alpha_phiphi and beta_phiphicomponent are well reproduced by expressions obtained under the SOCA, with agood matching of amplitude requiring a turbulent correlation time about fivetimes smaller than the estimated turnover time of the small-scale turbulentflow. We find the magnetic quenching of the alpha-effect to be driven primarilyby a reduction of the small-scale flow's kinetic helicity, with variations ofthe current helicity playing a lesser role in most locations in the simulationdomain. Our measurements of turbulent diffusivity quenching are restricted tothe beta_phiphi component, but indicate a weaker quenching, by a factor of1.36, than of the alpha effect, which in our simulation drops by a factor ofthree between the minimum and maximum phases of the magnetic cycle.

Characterisation of the turbulent electromotive force and its magnetically-mediated quenching in a global EULAG-MHD simulation of solar convection