  To study the complexity of hot Jupiter atmospheres revealed by observations
of increasing quality, we have adapted the UK Met Office global circulation
model (GCM), the Unified Model (UM), to these exoplanets. The UM solves the
full 3D Navier-Stokes equations with a height-varying gravity, avoiding the
simplifications used in most GCMs currently applied to exoplanets. In this work
we present the coupling of the UM dynamical core to an accurate radiation
scheme based on the two-stream approximation and correlated-k method with
state-of-the-art opacities from ExoMol. Our first application of this model is
devoted to the extensively studied hot Jupiter HD 209458b. We have derived
synthetic emission spectra and phase curves, and compare them to both previous
models also based on state-of-the-art radiative transfer, and to observations.
We find a reasonable a agreement between observations and both our day side
emission and hot spot offset, however, our night side emission is too large.
Overall our results are qualitatively similar to those found by Showman et al.
(2009) with the SPARC/MITgcm, however, we note several quantitative
differences: Our simulations show significant variation in the position of the
hottest part of the atmosphere with pressure, as expected from simple timescale
arguments, and in contrast to the "vertical coherency" found by Showman et al.
(2009). We also see significant quantitative differences in calculated
synthetic observations. Our comparisons strengthen the need for detailed
intercomparisons of dynamical cores, radiation schemes and post-processing
tools to understand these differences. This effort is necessary in order to
make robust conclusions about these atmospheres based on GCM results.
