What Makes the Sun Tick? - The Origin of the Solar Cycle
  In contrast to the situation with the geodynamo, no breakthrough has been made in the solar dynamo problem for decades. Since the appearance of mean-field electrodynamics in the 1960's, the only really significant advance was in the field of flux tube theory and flux emergence calculations. These new results, together with helioseismic evidence, have led to the realization that the toroidal magnetic flux giving rise to activity phenomena must be stored and presumably generated below the convection zone proper, in what I will call the DOT (Dynamo-Overshoot-Tachoclyne) layer. The only segment of the problem we can claim to basically understand is the transport of flux from this layer to the surface. On the other hand, as reliable models for the DOT layer do not exist we are clueless concerning the precise mechanisms responsible for toroidal/poloidal flux conversion and for characteristic migration patterns (extended butterfly diagram) and periodicities. Even the most basic result of mean-field theory, the interpretation of the butterfly diagram as an alpha-omega dynamo wave, has been questioned. This review therefore will necessarily ask more questions than give answers. Some of these key questions are   - Structure of the DOT layer   - alpha-quenching and distributed dynamo   - High-latitude migration patterns and their interpretation   - The ultimate fate of emerged flux 
K. Petrovay