The UK Met Office GCM with a sophisticated radiation scheme applied to the hot Jupiter HD 209458b
Astronomy and Astrophysics
EDP Sciences for European Southern Observatory (ESO)
To study the complexity of hot Jupiter atmospheres revealed by observations of increasing quality, we have adapted the UK Met Off ce 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 o set, 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 diff erences: 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 diff erences 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.
We would like to thank Jonathan Tennyson and Travis Barman for insightful discussions. This work is partly supported by the European Research Council under the European Community’s Seventh Framework Programme (FP7/2007-2013 Grant Agreement No. 247060-PEPS and grant No. 320478-TOFU). DSA acknowledges support from the NASA Astrobiology Program through the Nexus for Exoplanet System Science. NM acknowledges funding from the Leverhulme Trust via a Research Project Grant. JM and CS acknowledge the support of a Met Office Academic Partnership secondment. DH acknowledges funding from the DFG through the Collaborative Research Centre SFB 881 “The Milky Way System”. The calculations for this paper were performed on the University of Exeter Supercomputer, a DiRAC Facility jointly funded by STFC, the Large Facilities Capital Fund of BIS, and the University of Exeter.
This is the author accepted manuscript. The final version is available from EDP Sciences via the DOI in this record.
Online 26 August 2016