  We explore effects of random non-axisymmetric perturbations of kinetic
helicity (the $\alpha$ effect) and diffusive decay of bipolar magnetic regions
on generation and evolution of large-scale non-axisymmetric magnetic fields on
the Sun. Using a reduced 2D nonlinear mean-field dynamo model and assuming that
bipolar regions emerge due to magnetic buoyancy in situ of the large-scale
dynamo action, we show that fluctuations of the $\alpha$ effect can maintain
the non-axisymmetric magnetic fields through a solar-type $\alpha^{2}\Omega$
dynamo process. It is found that diffusive decay of bipolar active regions is
likely to be the primary source of the non-axisymmetric magnetic fields
observed on the Sun. Our results show that the non-axisymmetric dynamo model
with stochastic perturbations of the $\alpha$ effect can explain periods of
extremely high activity (`super-cycle' events) as well as periods of deep
decline of magnetic activity. We compare the models with synoptic observations
of solar magnetic fields for the last four activity cycles, and discuss
implications of our results for interpretation of observations of stellar
magnetic activity.

Solar and Stellar Astrophysics