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Abstract

We present simulations of the climate dynamics of condensible-rich atmospheres using a hierarchy of planetary climate models. A key different feature in our model compared to other models studying the moist climates is that we especially develop a simple parameterization of moist convection valid in the nondilute as well as dilute limits. The new convection scheme is used to discuss the basic character of nondilute convection. The energy conservation properties of the scheme are discussed in detail, and are verified in one-dimensional radiative- convective simulations. As a further illustration of the behavior of the scheme, results for a runaway greenhouse atmosphere for seasonally varying instellation corresponding to a highly eccentric orbit are presented. This case illustrates that the high thermal inertia associated with latent heat in nondilute atmospheres can damp out the effects of even extreme seasonal forcing.,We then develop a 3D idealized general circulation model that incorporates the 1D single column model, and use it to study condensible-rich atmospheres. We find that nondilute atmospheres have weak horizontal temperature gradients even for rapidly rotating planets, and that their circulations are largely barotropic. The relative humidity of the condensible component tends towards 100% as the atmosphere becomes more nondilute, which has important implications for runaway greenhouse thresholds.,We then shift our focus to condensible-rich atmospheres on slowly and synchronously rotating planets, because the atmospheres on such terrestrial exoplanets would be charac- terized by near-future telescopes, and fruitful observation results are expected to come out in the coming decade. We first study the moist climates governed by an overturning circulation with a weak cold trap. The simulation suggests high-level cloud formation near the substellar region and build up of condensible substance on the nightside. We next use a one-dimensional energy budget model to study the more strongly nondilute atmosphere governed by low-level evaporation-driven flow, and derive a non-dimensional parameter that determines whether the atmosphere is global or local. We discuss the possibility to discriminate the circulation regimes of condensible-rich atmospheres by using the broadband phase curve. Our finding will facilitate characterizing condensible atmospheres on tidally locked terrestrial exoplanets in the near future, including the habitable worlds when the condensible substance is water vapor.

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