Internal rotation in the Sun, showing differential rotation in the outer convective region and almost uniform rotation in the central radiative region. The transition between these regions is called the tachocline.
is the transition region of the Sun
between the radiative interior and the differentially rotating
outer convective zone. It is in the outer third of the Sun (by radius). This causes the region to have a very large shear
as the rotation rate changes very rapidly. The convective exterior rotates as a normal fluid with differential rotation with the poles rotating slowly and the equator rotating quickly. The radiative interior exhibits solid-body rotation, possibly due to a fossil field
. The rotation rate through the interior is roughly equal to the rotation rate at mid-latitudes, i.e. in-between the rate at the slow poles and the fast equator. Recent results from helioseismology
indicate that the tachocline is located at a radius of at most 0.70 times the Solar radius (measured from the core, i.e., the surface is at 1 solar radius), with a thickness of 0.04 times the solar radius. This would mean the area has a very large shear profile that is one way that large scale magnetic fields can be formed. The geometry and width of the tachocline plays an important role in models of the solar dynamo
by winding up weaker poloidal
field to create a much stronger toroidal
field. The term tachocline
was coined in a paper by Edward Spiegel
and Jean-Paul Zahn
by analogy to the oceanic thermocline
- ^ Spiegel, E.~A., & Zahn, J.-P., 1992, Astronomy and Astrophysics, 265, 106 
- Charbonneau, P., Christensen-Dalsgaard, J., Henning, R., Larsen, R.M., Schou, J., Thompson, M.J., Tomczyk, S., 1999a, “Helioseismic Constraints on the Structure of the Solar Tachocline”, Astrophys. J., 527, 445-460, .
- Basu, S., Antia, H.M., Narasimha, D., 1994, “Helioseismic Measurement of the Extent of Overshoot Below the Solar Convection Zone”, Mon. Not. R. Astron. Soc., 267, 209-224, 
- Hughes, D.W., Rosner, R., Weiss, N.O. 2007 The Solar Tachocline, 382pp (Cambridge University Press).
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