The solar tachocline.

Acoustic sounding of the Sun reveals that the variation of angular velocity with latitude is independent of depth in the convection zone. By contrast, deep within the radiative zone, the rotation appears to be rigid. The transition between the two rotation laws occurs in a thin, unresolved layer that the authors here call the tachocline. This paper is an examination of the structure and previous evolution of this layer. It is assumed that the stress exerted by the convection zone is prescribed, much as oceanographers take the wind stress on the sea surface as given. It is concluded that the helioseismic observations are best rationalized by a scenario in which, after an initial adjustment or spindown period, the subconvective rotation settles into a quasisteady state with a turbulent boundary layer. In the tachocline, the advection of angular momentum is controlled by horizontal turbulence. If this turbulence is intense enough, the tachocline is thin and is unresolved.