  We characterize and analyze rotational torsional oscillations developing in a
large-eddy magnetohydrodynamical simulation of solar convection (Ghizaru,
Charbonneau, and Smolarkiewicz, Astrophys. J. Lett., 715, L133 (2010); Racine
et al., Astrophys. J., 735, 46 (2011)) producing an axisymmetric large-scale
magnetic field undergoing periodic polarity reversals. Motivated by the many
solar-like features exhibited by these oscillations, we carry out an analysis
of the large-scale zonal dynamics. We demonstrate that simulated torsional
oscillations are not driven primarily by the periodically-varying large-scale
magnetic torque, as one might have expected, but rather via the magnetic
modulation of angular-momentum transport by the large-scale meridional flow.
This result is confirmed by a straightforward energy analysis. We also detect a
fairly sharp transition in rotational dynamics taking place as one moves from
the base of the convecting layers to the base of the thin tachocline-like shear
layer formed in the stably stratified fluid layers immediately below. We
conclude by discussing the implications of our analyses with regards to the
mechanism of amplitude saturation in the global dynamo operating in the
simulation, and speculate on the possible precursor value of torsional
oscillations for the forecast of solar cycle characteristics.
