  The advent of helioseismology has determined in detail the average rotation
rate of the Sun as a function of radius and latitude. These data immediately
reveal two striking boundary layers of shear in the solar convection zone (CZ):
a tachocline at the base, where the differential rotation of the CZ transitions
to solid-body rotation in the radiative zone, and a 35-Mm-thick near-surface
shear layer (NSSL) at the top, where the rotation rate slows by about 5% with
increasing radius. Though asteroseismology cannot probe the differential
rotation of distant stars to the same level of detail that helioseismology can
achieve for the Sun, it is possible that many cool stars with outer convective
envelopes possess similar differential rotation characteristics, including both
a tachocline and a NSSL. Here we present the results of 3D global hydrodynamic
simulations of spherical-shell convection for a Sun-like star at different
levels of density contrast across the shell. The simulations with high
stratification possess characteristics of near-surface shear, especially at low
latitudes. We discuss in detail the dynamical balance of torques giving rise to
the NSSL in our models and interpret what these balances imply for the real
Sun. We further discuss the dynamical causes that may serve to wipe out
near-surface shear at high latitudes, and conclude by offering some theories as
to how this problem might be tackled in future work.
