Simplified model for an alpha(2)-omega dynamo fed by dynamical evolution of the zonal shear

Recent solar observations pointed out the presence of a 2-yr periodicity superposed on the main 11 yr cycle, showing how different time-scales characterize the solar magnetic variability. A new model, presented here, interpreted the presence of time-scales smaller than the predominant period of 11 years, as due to a non-linear coupling of the magnetic field with a time-dependent omega effect. The latter is described by the evolution of the zonal shear, dynamically integrated with the induction equation. The model is built up retaining the main physical ingredients concurring to the dynamo effect by modelling the equations in terms of sources and sinks. In this way, a low-order alpha(2) - omega dynamo model is obtained and then numerically solved. The results show an oscillatory behaviour of the magnetic field components reproducing a basic cycle and superimposed characteristic smaller time-scales different from the frequency of the source terms. Moreover, a double-peaked structure has been found during the maxima of the magnetic field strength, resembling the behaviour of the solar activity as seems to be revealed by several solar cycle indicators. A phase shift between the poloidal and toroidal magnetic field components is also obtained.