Tachocline

The tachocline is the transition region of stars of more than 0.3 solar masses, between the radiative interior and the differentially rotating outer convective zone.

The radiative interior exhibits solid-body rotation, possibly due to a fossil field.

The geometry and width of the tachocline are thought to play an important role in models of the stellar dynamos by winding up the weaker poloidal field to create a much stronger toroidal field.

Recent radio observations of cooler stars and brown dwarfs, which do not have a radiative core and only have a convective zone, demonstrate that they maintain large-scale, solar-strength magnetic fields and display solar-like activity despite the absence of tachoclines.

[1] The term tachocline was coined in a paper by Edward Spiegel and Jean-Paul Zahn in 1992[2] by analogy to the oceanic thermocline.

An illustration of the structure of the Sun
Internal rotation in the Sun, showing differential rotation in the outer convective region (as a function of latitude) and almost uniform rotation in the central radiative region. The transition between these regions is called the tachocline. To convert the y-axis to period, use 500 nanoHz = 23.15 days.