A physically derived eddy parameterization for giant planet atmospheres with application on hot-Jupiter atmospheres

Abstract

We present a parameterization for the eddy diffusion profile of gas giant exoplanets based on physical phenomena and we explore how the parameterized eddy profile impacts the chemical composition, the thermal structure, the haze microphysics, and the transit spectra of 8 hot-Jupiters. Our eddy parameterization depends on the planetary intrinsic temperature (T$_{int}$ ), we thus evaluate how the increase of this parameter to values higher than those typically used ($\sim$100K) impacts the atmospheric structure and composition. Our investigation demonstrates that despite the strong impact of T$_{int}$ on the chemical composition of the deep atmosphere, the upper atmosphere is not affected for T$_{eq}$ $>$ 1300 K owing to high altitude quench levels at these conditions. Below this threshold, however, the larger atmospheric temperatures produced by increasing T$_{int}$ affect the quenched chemical composition. Our parameterization depends on two parameters, the eddy magnitude at the radiative-convective boundary (K$_0$) and the corresponding magnitude at the homopause (K$_{top}$). We demonstrate that, when using common K$_0$ and K$_{top}$ values among most of the different planet cases studied, we derive transit spectra consistent with Hubble Space Telescope observations. Moreover, our simulations show that increasing the eddy profile enhances the photochemical production of haze particles and reduces their average radius, thus providing a steeper UV-Visible slope. Finally, we demonstrate for WASP-39b that the James Webb Space Telescope observations provide improved constraints for the hazes and clouds and we show that both components seem necessary to interpret the combined transit spectrum from HST and JWST observations.