  We show that the MHD theory that explains the solar tachocline by an effect
of the magnetic field can work with the decay modes of a fossil field in the
solar interior if the meridional flow of the convection zone penetrates
slightly the radiative zone beneath. An equatorward flow of about 10 m/s
penetrating to a maximum depth of 1000 km below the convection zone is able to
generate almost horizontal field lines in the tachocline region so that the
internal field is almost totally confined to the radiative zone. The theory of
differential solar rotation indeed provides meridional flows of about 10 m/s
and a penetration depth of < 1000 km for viscosity values that are
characteristic of a stable tachocline.

Astrophysics