  We present self-consistent numerical simulations of the sun's convection zone
and radiative interior using a two-dimensional model of its equatorial plane.
The background reference state is a one-dimensional solar structure model.
Turbulent convection in the outer convection zone continually excites gravity
waves which propagate throughout the stable radiative interior and deposit
their angular momentum. We find that angular velocity variations in the
tachocline are driven by angular momentum transported by overshooting
convective plumes rather than the nonlinear interaction of waves. The mean flow
in the tachocline is time dependent but not oscillatory in direction. Since the
forcing in this shallow region can not be described by simple linear waves, it
is unlikely that the interaction of such waves is responsible for the solar
cycle or the 1.3 year oscillation. However, in the deep radiative interior, the
interaction of low amplitude gravity waves, continually excited by the
overshooting plumes, is responsible for the angular velocity deviations
observed there. Near the center of the model sun the angular velocity deviation
is about two orders of magnitude greater than that in the bulk of the radiative
region and reverses its direction (prograde to retrograde or vice versa) in the
opposite sense of the angular velocity deviations that occur in the tachocline.
Our simulations thus demonstrate how angular velocity variations in the solar
core are linked to those in the tachocline, which themselves are driven by
convective overshooting.

Astrophysics