  We perform a mean-field analysis of the EULAG-MHD millenium simulation of
global magnetohydrodynamical convection presented in Passos et al. 2014. The
turbulent electromotive force operating in the simulation is assumed to be
linearly related to the cyclic axisymmetric mean magnetic field and its first
spatial 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 the
simulation data through a least-squares minimization procedure based on
singular value decomposition. The reconstructed alpha-tensor shows good
agreement with that obtained by Racine et al. 2011, who did not include
derivatives of the mean-field in their fit, as well as with the alpha-tensor
extracted by Augustson et al. 2015 from a distinct ASH MHD simulation. The
isotropic part of the turbulent magnetic diffusivity tensor beta is positive
definite and reaches values of 5.0x10^7 m2s-1 in the middle of the convecting
fluid layers. The spatial variations of both alpha_phiphi and beta_phiphi
component are well reproduced by expressions obtained under the SOCA, with a
good matching of amplitude requiring a turbulent correlation time about five
times smaller than the estimated turnover time of the small-scale turbulent
flow. We find the magnetic quenching of the alpha-effect to be driven primarily
by a reduction of the small-scale flow's kinetic helicity, with variations of
the current helicity playing a lesser role in most locations in the simulation
domain. Our measurements of turbulent diffusivity quenching are restricted to
the beta_phiphi component, but indicate a weaker quenching, by a factor of
1.36, than of the alpha effect, which in our simulation drops by a factor of
three between the minimum and maximum phases of the magnetic cycle.
