  The magnetic fields of solar-type stars are observed to cycle over decadal
periods -11 years in the case of the Sun. The fields originate in the turbulent
convective layers of stars and have a complex dependency upon stellar rotation
rate. We have performed a set of turbulent global simulations that exhibit
magnetic cycles varying systematically with stellar rotation and luminosity. We
find that the magnetic cycle period is inversely proportional to the Rossby
number, which quantifies the influence of rotation on turbulent convection. The
trend relies on a fundamentally non-linear dynamo process and is compatible
with the Sun's cycle and those of other solar-type stars.
