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Characterising the circulation of temperate sub-Neptunes using 3D GCM simulations

Presentation #102.210 in the session Poster Session.

Published onJun 20, 2022
Characterising the circulation of temperate sub-Neptunes using 3D GCM simulations

In the last two decades, over a thousand sub-Neptune-sized exoplanets have been discovered by observational surveys. These planets, with extended, hydrogen-dominated atmospheres, have no solar-system analogues despite being one of the most abundant types of planet in our galaxy. With the advent of the James Webb Space Telescope, we expect the number of temperate sub-Neptunes with atmospheres characterised by transmission spectroscopy to increase greatly, but we have limited knowledge of their atmospheric circulations. We use the ExoFMS GCM with a simple semi-grey radiation scheme to simulate a range of temperate sub-Neptune atmospheres, in the hope of providing a baseline for the study of their dry dynamics. Using K2-18b as our fiducial case, we find atmospheres that are characterised by weak horizontal temperature gradients and high-latitude cyclostrophic jets. These features are robust across a range of temperate instellations and rotation periods. The predominant overturning circulation is from dayside to nightside, and we derive scaling relations linking the strength of the circulation and vertical velocities to the instellation. We compare our results to a previous study of K2-18b’s atmosphere (Charnay 2021) and find significant variations in the jet structures between our two models, highlighting the need for GCM intercomparisons in this area. Finally, we present preliminary results on the effect of latent heating and clouds on these circulations, using a simplified cloud scheme.

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