Category Archives: Exeter Exoplanets

National Astronomical Meeting 2014

Abstract submitted for the annual UK National Astronomical Meeting:

We are developing a tool to simulate the atmospheric chemistry of exoplanets, Solar System planets and the early-Earth. We are coupling a chemical network to an existing radiative-convective equilibrium model (Atmo) to study disequilibrium chemistry in 1D. This 1D chemistry model will be able to act as a stand-alone tool but will also be coupled to the Met Office Unified Model (UM); a fully-compressible, non-hydrostatic global circulation model. We will initially apply this model to study hot Jupiter atmospheres, primarily focusing on the formation of high altitude haze which observations increasingly show to be common in these atmospheres.

 

Initial tests of the 1D model show that we successfully reproduce equilibrium chemistry. Vertical mixing and photochemistry are being tested currently. We are also performing an analysis of uncertainty in chemical kinetic data, which has the potential to significantly affect the chemical abundances particularly for quenching species such as methane and ammonia (Drummond, Tremblin, Baraffe et al. in prep). Preliminary results of this work will be presented as well as an outline of the future plans to apply this flexible model to a range of different planetary atmospheres.

 

We aim to build a ‘planetary simulator’ applicable to any arbitrary planet and this project focuses on the chemistry. Most past photochemical studies have utilised a 1D model only and inherently 3D processes and characteristics are not correctly represented or lacking entirely.  Coupling disequilibrium chemistry with the 3D UM will provide further understanding of the chemical composition of these atmospheres.

Fingers crossed for a talk.

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A Step Forward for the Planetary Simulator

In another step forward of adapting the Unified Model (UM), a sophisticated 3D atmosphere model, to the extreme conditions of hot Jupiter exoplanets a new paper from our group explains the alterations to the radiative transfer scheme.

This latest paper by David Skålid Amundsen (http://arxiv.org/pdf/1402.0814.pdf) tests the Edwards-Slingo radiation scheme when applied to hot Jupiter type atmospheres. It utilises two approximations; one for the radiative transfer itself, the two stream approximation, and one for the opacity source of the atmosphere, the correlated k-method. The two stream approximation simplifies matters by assuming that radiation only travels in two directions, up and down. The correlated k-method involves a specific way of averaging millions of separate lines of a very high-resolution data set which describes how the radiation interacts with molecules in the atmosphere. Tackling this data-set fully would require an infeasible amount of computing time and the correlated k-method reduces this.

This study updated the molecular line list, used to calculate the opacity of the atmosphere, to be suitable for high temperatures of hot Jupiter atmospheres. Subsequent tests of this updated radiation scheme with a detailed (slow) model, Atmo, showed that these two approximations introduce no more than 10% error into the heating rates, yet reduce computation time by a factor of ~100.

Blue- The low temperature molecular line list used in the UM for Earth simulations. Green- The high temperature molecular line list used in this study.

Blue- The low temperature molecular line list used in the UM for Earth simulations. Green- The high temperature molecular line list used in this study. – D. S. Amundsen

These tests show the adaptations of the radiation scheme to high temperatures have resulted in a fast yet accurate radiative transfer model. The next stages will be to couple this radiation scheme with the UM to investigate the coupled effects dynamics and radiation in a 3D model.