  The magnetic activity of late-type stars is correlated with their rotation
rates. Up to a certain limit, stars with smaller Rossby numbers, defined as the
rotation period divided by the convective turnover time, have higher activity.
A more detailed look at this rotation-activity relation reveals that, rather
than being a simple power law relation, the activity scaling has a shallower
slope for the low-Rossby stars than for the high-Rossby ones. We find that, for
the chromospheric CaII H&K activity, this scaling relation is well modelled by
a broken two-piece power law. Furthermore, the knee-point of the relation
coincides with the axisymmetry to non-axisymmetry transition seen in both the
spot activity and surface magnetic field configuration of active stars. We
interpret this knee-point as a dynamo transition between dominating axi- and
non-axisymmetric dynamo regimes with a different dependence on rotation and
discuss this hypothesis in the light of current numerical dynamo models.
