  To understand and compare the 3D atmospheric structure of HD 209458 b and HD
189733 b, focusing on the formation and distribution of cloud particles, as
well as their feedback on the dynamics and thermal profile. We couple the 3D
Met Office Unified Model (UM), including detailed treatments of atmospheric
radiative transfer and dynamics, to a kinetic cloud formation scheme. The
resulting model self--consistently solves for the formation of condensation
seeds, surface growth and evaporation, gravitational settling and advection,
cloud radiative feedback via absorption and, crucially, scattering. Fluxes
directly obtained from the UM are used to produce synthetic SEDs and phase
curves. Our simulations show extensive cloud formation in both planets,
however, cooler temperatures in the HD 189733 b result in higher cloud particle
number densities. Sub-micron particles are suspended by vertical flows leading
to extensive upper-atmosphere cloud cover. A combination of meridional
advection and efficient cloud formation in cooler high latitude regions, result
in enhanced cloud coverage for latitudes > 30 degrees and leads to a zonally
banded structure for all our simulations. The cloud bands extend around the
entire planet(s), as the temperatures, even on the day side, remain below the
condensation temperature of silicates and oxides. Therefore, our simulated
optical phase curve for HD 209458 b shows no `offset', in contrast to
observations. Efficient scattering by cloud results an atmospheric cooling of
up to 250K, and an advection-driven fluctuating cloud opacity causes temporal
variability in the thermal emission. The inclusion of this fundamental
cloud-atmosphere radiative feedback leads to significant differences with
approaches neglecting these physical elements and suggests both a note of
caution of interpretations neglecting such cloud feedback and scattering, and
merits further study.
