A solar-like dynamo driven by magnetic buoyancy

The Sun's magnetic field is produced by a dynamo process operating deep below the solar surface. Magnetic buoyancy – the tendency for regions of strong magnetic field to be lighter than their surroundings – is certainly involved in the transport of field to the surface, but is not usually thought to play a role in the generation of the field itself. However, we have recently shown that magnetic buoyancy instability operating just below the Sun's convection zone, in the strongly sheared "tachocline", can contribute to the generation of large-scale poloidal field, which is the most elusive step in solar dynamo models. We also have preliminary results, using numerical simulations in a local Cartesian model, demonstrating that a combination of shear and magnetic buoyancy can produce a cyclic, migratory dynamo analogous to that of the Sun. We propose to extend these results to geometries that are more representative of the solar interior, beginning with an equatorial beta-plane model and then moving on to a full spherical shell. Our goal is to show that a solar-type dynamo can be achieved using just the physical processes – shear and magnetic buoyancy – known to be operating in the tachocline. If successful, this will revolutionise our understanding of the solar dynamo (and dynamos in solar-type stars more generally).