The competition in the solar dynamo between surface and deep-seated α-effects

The solar magnetic field is generated by the action of a hydromagnetic dynamo. Although there is a consensus that the site for the production of the toroidal magnetic field is the region of strong shear ( differential rotation) at the base of the solar convection zone, there are two competing theories for the site of the production of the poloidal field. In the early models of Babcock and Leighton, the poloidal field is produced by the decay of active regions at the solar surface, while in interface dynamo models, it is produced near the base of the solar convection zone, either by the action of cyclonic turbulence or via the instability of a magnetic layer. Here we discuss the pros and cons of these two scenarios and present results that demonstrate that, owing to the proximity of the regeneration region to the region of strong shear, the interface dynamo is considerably more effective than the surface dynamo-even if the mechanism for regenerating the poloidal field at the base of the solar convection zone is substantially weaker.