  Radiation-dust driven outflows, where radiation pressure on dust grains
accelerates gas, occur in many astrophysical environments. Almost all previous
numerical studies of these systems have assumed that the dust was
perfectly-coupled to the gas. However, it has recently been shown that the dust
in these systems is unstable to a large class of resonant drag instabilities
(RDIs) which de-couple the dust and gas dynamics and could qualitatively change
the nonlinear outcome of these outflows. We present the first simulations of
radiation-dust driven outflows in stratified, inhomogeneous media, including
explicit grain dynamics and a realistic spectrum of grain sizes and charge,
magnetic fields and Lorentz forces on grains (which dramatically enhance the
RDIs), Coulomb and Epstein drag forces, and explicit radiation transport
allowing for different grain absorption and scattering properties. In this
paper we consider conditions resembling giant molecular clouds (GMCs), HII
regions, and distributed starbursts, where optical depths are modest,
single-scattering effects dominate radiation-dust coupling, Lorentz forces
dominate over drag on grains, and the fastest-growing RDIs are similar, such as
magnetosonic and fast-gyro RDIs. These RDIs generically produce strong
size-dependent dust clustering, growing nonlinear on timescales that are much
shorter than the characteristic times of the outflow. The instabilities produce
filamentary and plume-like or 'horsehead' nebular morphologies that are
remarkably similar to observed dust structures in GMCs and HII regions.
Additionally, in some cases they strongly alter the magnetic field structure
and topology relative to filaments. Despite driving strong micro-scale dust
clumping which leaves some gas behind, an order-unity fraction of the gas is
always efficiently entrained by dust.
