  We study line driven stellar winds using time-dependent radiation
hydrodynamics where the continuum radiation couples to the gas via either a
scattering or absorption opacity and there is an additional radiation force due
to spectral lines that we model in the Sobolev approximation. We find that in
winds with scattering opacities, instabilties tend to be suppressed and the
wind reaches a steady state. Winds with absorption opacities are unstable and
remain clumpy at late times. Clumps persist because they are continually
regenerated in the subcritical part of the flow. Azimuthal gradients in the
radial velocity distribution cause a drop in the radial radiation force and
provide a mechanism for generating clumps. These clumps form on super-Sobolev
scales, but at late times become Sobolev-length sized indicating that our
radiation transfer model is breaking down. Inferring the clump distribution at
late times therefore requires radiation-hydrodynamic modeling below the Sobolev
scale.
