Propagation of a dynamo ®eld in the radiative interior of the Sun

AB S TRACT Large-scale magnetic ®elds are believed to play an important role in the radiative zone of the Sun, in particular in the dynamical processes in the transition region between the convective and radiative zones (the tachocline). Also, they are probably responsible for the observed uniform rotation of the radiative zone. In that respect, since it has been suggested that the solar dynamo may lie near the outer edge of the tachocline, it is important to assess the question of how deep the dynamo ®eld can penetrate, and whether it can in ̄uence signi®cantly the dynamics of the solar interior. The magnetic cycle of the Sun is not strictly periodic, but undergoes random ̄uctuations in amplitude and phase. It is shown how the random ̄uctuations in the poloidal ®eld diffuse into the radiative zone. An explicit solution for this diffusion process is given under certain simplifying assumptions. The result is then used together with some assumptions about the solar dynamo ®eld to suggest that a ®eld of order of 10 G should be expected near the outer edge of the radiative zone, dropping rapidly to 10 G beneath r ˆ 0:3R(. This con®rms the expectation that the dynamo ®eld has a negligible effect on the dynamical processes taking place both in the tachocline and deeper in the radiative zone.