  The evolution of the solar activity comprises, apart from the well-known
11-year cycle, various temporal scales ranging from months up to the secondary
cycles known as mid-term oscillations. Its nature deserves a physical
explanation. In this work, we consider the 5-to-6 year oscillations as derived
both from sunspot and from solar magnetic dipole time series. Using the solar
dynamo model, we deduced that these variations may be a manifestation of the
dynamo nonlinearities and non-harmonic shape of the solar activity cycles. We
conclude that the observed mid-term oscillations are related to the nonlinear
saturation of the dynamo processes in the solar interior.
