The solar magnetic fields are far from being earth-like, dipolar configurations, consisting instead of a wide range of length-scales and strengths. Interestingly, the large-scale solar magnetic fields evolve in a cyclic fashion with a 22-year periodicity. A magnetohydrodynamic dynamo operating in the Sun is most likely to be responsible for producing the solar magnetic activity cycle. The first dynamo models, built about half a century ago, involved two basic processes: (i) generation of toroidal fields by shearing the pre-existing poloidal fields by differential rotation (the Ω-effect), (ii) re-generation of poloidal fields by lifting and twisting the toroidal fluxtubes (the α-effect). Until the 1980's, these models remained the favored explanatory models for the periodic evolution of sunspots -- the best known manifestation of the solar activity cycle. But due to the increasing number of observational constraints being revealed to us over the past decades, the current status of the large-scale solar dynamo mechanism differs significantly from that of early models. After briefly reviewing the historical evolution of solar dynamo models, we will present the recent flux-transport type dynamo models. We will close by demonstrating how this class of models can be applied for predicting the mean amplitudes and durations of the upcoming solar cycles.
References:
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