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 :3. 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 (17), 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 minimal yet reasonably realistic choices.
It should be noted already that such a solar-like differential rotation profile is quite complex from the point of view of dynamo modelling, in that it is characterized by three partially overlapping shear regions: a strong positive radial shear in the equatorial regions of the tachocline, an even stronger negative radial shear in its the polar regions, and a significant latitudinal shear throughout the convective envelope and extending partway into the tachocline. As shown in panel B of Figure 5, for a tachocline of half-thickness , the mid-latitude latitudinal shear at is comparable in magnitude to the equatorial radial shear; its potential contribution to dynamo action should not be casually dismissed.
Living Rev. Solar Phys. 7, (2010), 3
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