Quantifying the differences in transmission and emission spectra of hot irradiated gaseous exoplanet atmospheres: a comparison of 1D and 3D modelling using <i>JWST</i>

ABSTRACT Modelling the atmospheres of exoplanets is fundamental to understanding their atmospheric physics and chemical processes. While 1D atmospheric models with 1D radiative transfer (RT) have been widely used, advances in 3D general circulation models (GCMs) and 3D RT methods now allow quantitative comparisons of these approaches. With the precision and sensitivity of James Webb Space Telescope (JWST), such differences can be observationally tested. This study investigates the spectral variations produced by 1D and 3D models and estimates the JWST observing time or number of transits needed to distinguish them. Using HD 189733b as a case study, three sets of simulations were performed: 1D atmospheric models with 1D RT and 3D GCM models coupled with both 1D and 3D RT. An inherent limitation of our study is that the temperature–pressure (T–P) profiles derived from the 3D GCM extend only to the high-pressure regions. The simulations incorporated both equilibrium and disequilibrium chemistry. Significant spectral discrepancies were found, with 3D models generally showing weaker features. Using a JWST noise simulator, the signal-to-noise ratio (SNR) for detecting these differences was calculated. For transmission spectra, the SNR ranged from 2.04–7.68 (equilibrium) and 1.66–7.04 (disequilibrium), while for emission spectra it ranged from 5.90–34.52 (equilibrium) and 7.11–36.93 (disequilibrium). To test the limitations of the 3D GCM, we extended the atmosphere to lower pressures using an isothermal T–P profile and found wavelength-dependent variations in both the spectra and the SNR. These results show that JWST can distinguish 1D from 3D model spectra for major molecular features, underscoring the importance of 3D modelling in interpreting exoplanetary atmospheres.