ABSTRACT
The observed properties of the magnetic field in the solar photosphere and theoretical studies of magneto-convection in electrically well-conducting fluids suggest that the magnetic field in stellar convection zones is quite inhomogeneous: magnetic flux is concentrated into magnetic flux tubes embedded in significantly less magnetized plasma. The storage of magnetic flux for periods comparable to the amplification time of the dynamo requires the compensation of magnetic buoyancy by a stably stratified medium, a situation realized in a layer of overshooting convection at the bottom of the convection zone. The major part of the magnetic flux at the surface of the Sun is not distributed in a diffuse manner, but appears in discrete structures, namely magnetic flux tubes, of which sunspots are the most prominent manifestation. The flux tube is idealized as a bundle of magnetic field lines, which is separated from its non-magnetic environment by a tangential discontinuity. Another important point is the stability of a magnetic layer.
