Penetration of dynamo-generated magnetic fields into the Sun's radiative interior

We show that a regular cyclic dynamo can also be the origin of strong magnetic fields in the solar radiative tachocline and interior below. By exploiting a kinematic, mean-field flux-transport dynamo, we show that for a wide range of core-diffusivity values, from 10⁹ cm² s⁻¹ down to a molecular diffusivity of 10³ cm² s⁻¹, oscillatory dynamo fields penetrate below the tachocline.

Amplitudes of these fields are in the range of ~1 kG to 3 × 10³ kG, depending on core diffusivity value, when the dynamo produces ~100 kG peak toroidal fields in the overshoot tachocline. For a low enough core diffusivity (≲10⁸ cm² s⁻¹), there is also a steady (nonreversing) dynamo in the radiative tachocline and below, which generates strong toroidal field of amplitude ~1 kG to 3 × 10³ kG or more there. The key elements in this dynamo are the low diffusivity, the differential rotation near the bottom of the tachocline, and an assumed tachocline α-effect.