Using a weather prediction code to model exoplanet atmospheres

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Weather prediction on the Earth, as anyone who has a weather-dependant hobby knows, is a tricky business. It is, however, something scientists have, over the last decade or so, got much better at. One of the leading centres for research on the Earth’s weather and climate is the UK Met Office. The Met Office uses simulations produce by a monstrous piece of complex software, a Global-Circulation-Model. This comprises the so-called “Unified Model”,  which models the Earth’s atmosphere, coupled to an ocean model, sea ice model and land surface model, to predict global and local (down to a resolution of ~1km) weather and the future (and past) climate of the Earth.

A Figure of pressure (colour map) and horizontal wind speed (arrows) at the top of the atmosphere for a simulation of HD209458b, mapped onto a sphere.

Now, that is all well and good but how much more fun would it be to use this code to model something much more extreme? In a process which is a little like taking a Lamborghini for a spin around a 4×4 off-roading course, a team of Exeter Physicists are attempting to adapt the Unified Model for use in modeling Hot-Jupiters.

I’m responsible for grappling the ~million lines of code  into submission, and in reality finding which 900,000 lines can be bypassed/thrown out! Many Earth-oriented circulation models have been adapted for the study of Solar or Extrasolar planets, and in all cases this is extremely challenging. What makes it hard is that we have to deal with day-night temperature contrasts more than  1000 K, wind speeds close to the speeed of sound and a dynamical atmosphere extending from a few mBar down to ~10kBar. So why do this with the Met Office code? Well because it is one of the most complete GCM models available. The code solves the equations of motion of the atmosphere without the raft of usual assumptions and simplifications, which in particular allows the solution of dynamical transport at very high pressures. This project is progressing well but we are still some way from predicting pollen counts on HD 209458 b.

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About Author

I am a Postdoctoral researcher at the University of Exeter. I started working with Prof. Isabelle Baraffe in November 2011 on a project to model the atmospheres of Hot Jupiters using a Global Circulation Model (GCM). My research history includes a Masters level research project on Surface Plasmon Resonance, a PhD in Stellar ages and observational astrophysics and a postdoctoral project on radiative transfer in brown dwarf accretion discs. (More)