  Context. The recently developed test-field method permits to compute dynamo
coefficients from global, direct numerical simulations. The subsequent use of
these parameters in mean-field models enables us to compare self-consistent
dynamo models with their mean-field counterparts. So far, this has been done
for a simulation of rotating magnetoconvection and a simple benchmark dynamo,
which are both (quasi-)stationary. Aims. It is shown that chaotically
time-dependent dynamos in a low Rossby number regime may be appropriately
described by corresponding mean-field results. Also, it is pointed out under
which conditions mean-field models do not match direct numerical simulations.
Methods. We solve the equations of magnetohydrodynamics (MHD) in a rotating,
spherical shell in the Boussinesq approximation. Based on this, we compute
mean-field coefficients for several models with the help of the previously
developed test-field method. The parameterization of the mean electromotive
force by these coefficients is tested against direct numerical simulations. In
addition, we use the determined dynamo coefficients in mean-field models and
compare the outcome with azimuthally averaged fields from direct numerical
simulations. Results. The azimuthally and time-averaged electromotive force in
fast rotating dynamos is sufficiently well parameterized by the set of
determined mean-field coefficients. In comparison to the previously considered
(quasi-)stationary dynamo, the chaotic time-dependence leads to an improved
scale separation and thus to a better agreement between direct numerical
simulations and mean-field results.

Solar and Stellar Astrophysics