Structure of the magnetic field in the lower convection zone

The properties of the magnetic field and the convective flows near the base of the solar convection zone are crucial for understanding the working of the solar dynamo. We consider three aspects of this complex problem. (i) Magnetic flux needs to be stored against buoyant loss for a sufficiently long time in order to be amplified by the dynamo process. Convective pumping in strongly stratified convection is probably not sufficient for the strong fields (of order 10⁵ G) which have been inferred from the simulations of rising flux tubes. The required subadiabatically stratified storage region is likely to be generated by the asymmetric flow field (strong coherent downflows, weak upflows) characteristic for compressible convection in a stratified medium. (ii) In a weakly subadiabatic region or a convective overshoot layer, the force equilibrium of a magnetic layer is very similar to that of an isolated flux tube: zero buoyancy and balance between the magnetic curvature (tension) force and the Coriolis force induced by a longitudinal flow along the field lines in a rotating system. In a strongly subadiabatic radiative region, a magnetic layer develops a different kind of force equilibrium, which involves buoyancy and a latitudinal pressure gradient.(iii) A field of 10⁵ G is difficult to generate by convection or differential rotation. The outflow of plasma from an 'exploded' flux tube provides an intensification mechanism which is not limited by the Lorentz force and converts potential energy of a superadiabatic stratification into magnetic energy.