Modeling the Atmospheres of Tidally Locked Exoplanets in N columns

Exoplanet atmosphere models face two competing demands. On the one hand atmospheres are shaped by a large number of physical processes, including radiative transfer; atmospheric chemistry; and fluid dynamics; and models that resolve all these processes in detail are computationally expensive. On the other hand quantitative comparison between models and exoplanet data requires that models be evaluated thousands of times, so models should be as fast as possible. As a result, state-of-the-art exoplanet retrieval models largely still focus on 1D radiative transfer, which means these models cannot resolve the physics of atmospheric fluid motions and large-scale transport.Here we present an N-column atmospheric model that bridges the gap between 1D and 3D, and is suitable for modeling tidally locked exoplanets. The physics of large-scale atmospheric fluid motions is represented using Weak-Temperature-Gradient (WTG) theory, a well-known framework from tropical meteorology. WTG theory allows us to parameterize both atmospheric heat transport and tracer redistribution. First, we test the N-column model using grey radiative transfer. The model successfully captures the main features of tidally locked rocky planets, as simulated by a 3D global climate model (GCM), but at a fraction of the computational cost. Second, we implement the N-column framework in HELIOS, a sophisticated radiative transfer model for exoplanet atmospheres. Finally, we explore the application of this modeling approach for observations and atmospheric retrievals of rocky exoplanets with near-future space telescopes.