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Abstract:
In anticipation of the next era of space telescopes for exoplanet characterization (James Webb, ARIEL) it is essential that sophisticated modeling tools for the atmospheres of transiting planets are developed. However, the associated effects of strong stellar irradiation and tidal locking make these objects inherently three-dimensional (3D) in nature, and multidimensional forward models are thus required to accurately simulate the multitude of processes that comprise an atmospheric system. This is especially the case for the out-of-equilibrium chemical composition, which is tightly coupled to the planetary climate through dynamical quenching and can show large longitudinal variations due to day-night temperature differences and photochemical reactions. Despite fast developments in the field, coupling 3D general circulation models (GCM) with radiative transfer and chemistry, computation times are a major bottleneck of these models and thus they are only applied to a small number of planets. In an effort to remedy this limitation, we employ a range of post-processed forward models in sequence: a 3D GCM (MITgcm, Adcroft+2004) with simplified, Newtonian radiative transfer (based on petitCODE, Mollière+ 2015), a post-processed pseudo-2D chemical network solver (Agundez+ 2014) and a ray-tracing code (petitRADTRANS, Mollière+ 2019), to compute an extensive grid of planetary atmospheres and synthetic transmission spectra. This allows us to study the mechanisms of disequilibrium chemistry and their effect on the observables in a systematic way for a large range of planets. More specifically, we report on the change in synthetic transmission spectra due to longitudinally-varying vertical mixing and photochemistry. This enables us to derive general parametrizations for these processes for implementation in 1D retrieval codes, a necessary step in preparing for the interpretation of high-quality data coming from the James Webb Space Telescope and ARIEL.
