  We present high resolution transmission spectra, calculated directly from a
3D radiative-hydrodynamics simulation that includes kinetic cloud formation,
for HD209458b. We find that the high opacity of our vertically extensive cloud
deck, composed of a large number density of sub-micron particles, flattens the
transmission spectrum and obscures spectral features identified in observed
data. We use the PandExo simulator to explore features of our HD209458b
spectrum which may be detectable with the James Webb Space Telescope (JWST). We
determine that an 8 - 12 micron absorption feature attributed to the
mixed-composition, predominantly silicate cloud particles is a viable marker
for the presence of cloud. Further calculations explore, and trends are
identified with, variations in cloud opacity, composition heterogeneity and
artificially scaled gravitational settling on the transmission spectrum.
Principally, by varying the upper extent of our cloud decks, rainout is
identified to be a key process for the dynamical atmospheres of hot-Jupiters
and shown to dramatically alter the resulting spectrum. Our synthetic
transmission spectra, obtained from the most complete, forward atmosphere
simulations to--date, allow us to explore the model's ability to conform with
observations. Such comparisons can provide insight into the physical processes
either missing, or requiring improvement.
