  Bistability and hysteresis of magnetohydrodynamic dipolar dynamos generated
by turbulent convection in rotating spherical fluid shells is demonstrated.
Hysteresis appears as a transition between two distinct regimes of dipolar
dynamos with rather different properties including a pronounced difference in
the amplitude of the axisymmetric poloidal field component and in the form of
the differential rotation. The bistability occurs from the onset of dynamo
action up to about 9 times the critical value of the Rayleigh number for onset
of convection and over a wide range of values of the ordinary and the magnetic
Prandtl numbers including the value unity.
