Helioseismology has pinned down with great accuracy the internal solar structure, including the internal differential rotation, and the exact location of the core-envelope interface. Unless noted otherwise, all illustrative models discussed in this section were computed using the following analytic formulae for the angular velocity and magnetic diffusivity :4. This rotational transition takes place across a spherical shear layer of half-thickness coinciding with the core-envelope interface at (see Figure 5, with parameter values listed in caption). As per Equation (19), a similar transition takes place with the net diffusivity, falling from some large, “turbulent” value in the envelope to a much smaller diffusivity in the convection-free radiative core, the diffusivity contrast being given by . Given helioseismic constraints, these represent minimalistic yet reasonably realistic choices.
Ultimately, the magnetic diffusivities and differential rotation in the convective envelope owe their existence to the turbulence therein, more specifically to the associated Reynolds stresses. While it has been customary in solar dynamo modelling to simply assume plausible functional forms for these quantities (such as Equations (17, 18, 19) above), one recent trend has been to calculate these quantities in an internally consistent manner using an actual model for the turbulence itself (see, e.g., Kitchatinov and Rüdiger, 1993). While this approach introduces additional - and often important - uncertainties at the level of the turbulence model, it represents in principle a tractable avenue out of the kinematic regime.
© Max Planck Society and the author(s)