The first multi-dimensional view of mass loss from externally FUV
  irradiated protoplanetary discs
  Computing the flow from externally FUV irradiated protoplanetary discs
requires solving complicated and expensive photodissociation physics
iteratively in conjunction with hydrodynamics. Previous studies have therefore
been limited to 1D models of this process. In this paper we compare
2D-axisymmetric models of externally photoevaporating discs with their 1D
analogues, finding that mass loss rates are consistent to within a factor four.
The mass loss rates in 2D are higher, in part because half of the mass loss
comes from the disc surface (which 1D models neglect). 1D mass loss rates used
as the basis for disc viscous evolutionary calculations are hence expected to
be conservative. We study the anatomy of externally driven winds including the
streamline morphology, kinematic, thermal and chemical structure. A key
difference between the 1D and 2D models is in the chemical abundances. For
instance in the 2D models CO can be dissociated at smaller radial distances
from the disc outer edge than in 1D calculations because gas is
photodissociated by radiation along trajectories that are assumed infinitely
optically thick in 1D models. Multidimensional models will hence be critical
for predicting observable signatures of environmentally photoevaporating
protoplanetary discs.
