The UK Met Office global circulation model with a sophisticated radiation scheme applied to the hot Jupiter HD 209458b

¹ Astrophysics Group, University of Exeter, Exeter, EX4 4QL, UK
² Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY 10025, USA
e-mail: d.s.amundsen@columbia.edu
³ NASA Goddard Institute for Space Studies, New York, NY 10025, USA
⁴ Université Lyon, ENS de Lyon, Université Lyon 1, CNRS, CRAL, UMR5574, 69007 Lyon, France
⁵ Met Office, Exeter, EX1 3PB, UK
⁶ Maison de la Simulation, CEA-CNRS-INRIA-UPS-UVSQ, USR 3441, Centre d’étude de Saclay, 91191 Gif-Sur-Yvette, France
⁷ Zentrum für Astronomie der Universität Heidelberg, Landessternwarte, Königstuhl 12, 69117 Heidelberg, Germany

Received: 24 June 2016
Accepted: 26 August 2016

Abstract

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 agreement between observations and both our days side emission and hot spot offset, however, our night side emissions is too large. Overall our results are qualitatively similar to those found by Showman et al. (2009, ApJ, 699, 564) 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.