Comparison between ozone column depths and methane lifetimes computed by one- and three-dimensional models at different atmospheric O ₂ levels

Abstract

Recently, Cooke et al . (Cooke et al . 2022 R. Soc. Open Sci. 9 , 211165. ( doi:10.1098/rsos.211165 )) used a three-dimensional coupled chemistry-climate model (WACCM6) to calculate ozone column depths at varied atmospheric O 2 levels. They argued that previous one-dimensional (1-D) photochemical model studies, e.g. Segura et al . (Segura et al . 2003 Astrobiology 3 , 689–708. ( doi:10.1089/153110703322736024 )), may have overestimated the ozone column depth at low pO 2 , and hence also overestimated the lifetime of methane. We have compared new simulations from an updated version of the Segura et al . model with those from WACCM6, together with some results from a second three-dimensional model. The discrepancy in ozone column depths is probably due to multiple interacting parameters, including H 2 O in the upper troposphere, lower boundary conditions, vertical and meridional transport rates, and different chemical mechanisms, especially the treatment of O 2 photolysis in the Schumann–Runge (SR) bands (175–205 nm). The discrepancy in tropospheric OH concentrations and methane lifetime between WACCM6 and the 1-D model at low pO 2 is reduced when absorption from CO 2 and H 2 O in this wavelength region is included in WACCM6. Including scattering in the SR bands may further reduce this difference. Resolving these issues can be accomplished by developing an accurate parametrization for O 2 photolysis in the SR bands and then repeating these calculations in the various models.

A Correlated‐K Parameterization for O2 Photolysis in the Schumann‐Runge Bands

“…The results, which were somewhat unexpected, are shown in Table 3 (Note: These results are not directly comparable to those shown in Ji, Kasting, et al. (2023), because the Ji et al. standard model did not include chlorine chemistry and because Ji et al.…”

“…The current paper was motivated by studies by Cooke et al (2022) and Ji, Kasting, et al (2023), in which the authors compared calculations of ozone column depth vs. atmospheric pO 2 using several different photochemical models. Two of these models received special attention: (a) the Kasting-group 1-D photochemical model (see, e.g., Kasting, 1979;Kasting et al, 1985;Segura et al, 2003), and (b) the (3-D) Whole Atmosphere Community Climate Model version 6, WACCM6, developed at the National Center for Atmospheric Research (Cooke et al, 2022;Gettelman et al, 2019).…”

Degenerate Interpretations of O3 Spectral Features in Exoplanet Atmosphere Observations Due to Stellar UV Uncertainties: A 3D Case Study with TRAPPIST-1 e

“…Based on previous results, it seems that stellar flares will exacerbate the interpretation of observed spectra, so future work on incoming UV uncertainties could evaluate the additional impact of stellar flares. The present modeling uncertainties in the O 2 -O 3 nonlinear relationship arising from differences in predictions between 1D and 3D models (Cooke et al 2022;Kozakis et al 2022;Yassin Jaziri et al 2022;Ji et al 2023) will compound this issue. In addition to previous work, our simulations, which focus on the specific target of TRAPPIST-1 e, further motivates the need for a dedicated next-generation observatory with UV capabilities to characterize exoplanet host stars.…”

“…The chemical mechanism, which is described in Emmons et al (2020), has 98 chemical species and 298 chemical reactions (including photochemical reactions). Absorption by CO 2 and H 2 O in the Schumann-Runge bands is included (Ji et al 2023). The full details of the model setup, alongside simulation scripts, are available via GitHub.…”

Global Chemical Transport on Hot Jupiters: Insights from the 2D VULCAN Photochemical Model

“…Modeling efforts have been put into implementing reduced chemical schemes in a GCM to account for transport-induced disequilibrium (Drummond et al 2020;Tsai et al 2022;Lee et al 2023). While Earth climate models have provided insights into the oxygen response of Earth-like atmospheres (Chen et al 2021;Cooke et al 2022;Braam et al 2023;Deitrick & Goldblatt 2023;Ji et al 2023), to date the incorporation of photochemistry into 3D models for diverse non-Earth-like atmospheres has not yet been realized.…”