June 7, 2013: General Circulation Modeling of Close-In Exoplanet Atmospheres

Many exoplanets are on close-in orbits and are likely tidally synchronized. Atmospheric circulation affects the temperature distribution and thus transit observations of these planets. In particular, hot spots shifted by broad, steady, superrotating jets have been emphasized in the literature, but vortices can also play an important role. The scale of jets and vortices is expected to be large for this type of planets, which makes their possible time variability crucial. Our goal is to explore dominant circulation patterns and constrain conditions and mechanisms for variability on tidally locked exoplanets.

We use a general circulation model, solving the primitive equations with thermal relaxation. The parameter space relevant for tidally synchronized planets is explored, using the mini-Neptune GJ1214b and hot Jupiter HD209458b as reference planets. Furthermore, results are compared from models using different numerical algorithms and grids for a range of relevant test cases.

For a large range of conditions, robust features include a small number of jets and large-scale vortices. The vortices often exhibit time variability, associated with planetary scale waves, with corresponding variability in the position of relative hot and cold regions.

The results make a strong case for mission concepts such as ESA’s EChO, that emphasize repeated measurements of a given planet. The feedback between such observations and modeling offers an opportunity to gain new insights into exoplanet atmospheres from the time modulation of the signals, in addition to spatial variability.

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