Code modifications in CESM2.1.3 for exoplanet and paleoclimate simulations

Authors: Greg Cooke (gjc53@cam.ac.uk, University of Cambridge, University of Leeds) & Dan Marsh (University of Leeds)

Introduction

This repository contains the code modifications necessary for simulating plaeoclimates and exoplanets with CESM2.1.3, specifically with WACCM6.

It details how to set up simulations, why the changes were made, as well as problems that were encountered.

Namelist file changes, boundary conditions, solar spectra input files, and source code modifications are given.

The location of restarts directories will also be given and are currently on the ARC4 supercomputer at the University of Leeds.

If anything is unclear, please get in touch with Greg at gjc53@cam.ac.uk.

Publications

• Cooke G. J., Marsh D. R., Walsh C., Youngblood A., 2023, Degenerate Interpretations of O3 Spectral Features in Exoplanet Atmosphere Observations Due to Stellar UV Uncertainties: A 3D Case Study with TRAPPIST-1 e, Astrophsical Journal, https://iopscience.iop.org/article/10.3847/1538-4357/ad0381/meta.
• Ji A., Kasting J. F., Cooke G. J., Marsh D. R. and Tsigaridis K. 2023, Comparison between ozone column depths and methane lifetimes computed by one- and three-dimensional models at different atmospheric O2 levels, R. Soc. open sci, 10230056230056, https://doi.org/10.1098/rsos.230056.
• G J Cooke, D R Marsh, C Walsh, S Rugheimer, G L Villanueva, Variability due to climate and chemistry in observations of oxygenated Earth-analogue exoplanets, Monthly Notices of the Royal Astronomical Society, Volume 518, Issue 1, January 2023, Pages 206–219, https://doi.org/10.1093/mnras/stac2604.
• Cooke G. J., Marsh D. R., Walsh C., Black B. and Lamarque J.-F. 2022, A revised lower estimate of ozone columns during Earth’s oxygenated history, R. Soc. open sci, 9211165211165, https://doi.org/10.1098/rsos.211165.

Varied O₂ simulations (paleoclimates / Earth-analogue exoplanets)

These simulations were used to calculate new ozone estimates from 0.1% the present atmospheric level (PAL) of O₂ to 150% PAL of O₂ - see Cooke et al. 2022. They were then used to predict time-varying direct imaging of Earth-analogue exoplanets - see Cooke et al. 2023.

Instructions on how to set up these cases are found in the O2_Earth_analogues_folder.

A list of cases (where PAL means present atmospheric level) are described in the table below:

Table 1

Simulation name	Description
Pre-industrial	Standard pre-industrial BWma1850 case
150% PAL	150% PAL of O2
50% PAL	50% PAL of O2
10% PAL	10% PAL of O2
10% PAL CH4 em10	10% PAL of O2 5000 Tg/yr CH4 flux
10% PAL CH4 em1	10% PAL of O2 500 Tg/yr CH4 flux
10% PAL CH4 em0.1	10% PAL of O2 50 Tg/yr CH4 flux
5% PAL	5% PAL O2
1% PAL	1% PAL of O2
1% PAL CH4 em10	1% PAL of O2 5000 Tg/yr CH4 flux
1% PAL CH4 em1	1% PAL of O2 500 Tg/yr CH4 flux
1% PAL CH4 em0.1	1% PAL of O2 50 Tg/yr CH4 flux
1% PAL 2 Ga YS	1% PAL of O2 2 Gyr younger Sun
1% PAL 2 Ga YS 4x CO2	1% PAL of O2 2 Gyr younger Sun with 1120 ppmv CO2
1% PAL 2 Ga YS 21 hr	1% PAL of O2 2 Gyr younger Sun with 21 hour day
0.5% PAL	0.5% PAL of O2
0.1% PAL	0.1% PAL of O2

Since these simulations were performed, we (Dan, Greg, and Doug Kinnison) have updated the source code to include absorption in the Schumann-Runge bands, and also added in previously missing cross sections. Whilst these updates do not make an appreciable difference for the pre-industrial atmosphere, it is now recommended to include these updates when investigating low-O₂ atmospheres (for Earth, this occurs at 1% PAL and lower). For the understanding of why this is important, see Ji et al., 2023. The following simulations were performed for Ji et al., 2023.

Table 2

Simulation name	Description
10% PAL 10x lower halogens	10% PAL of O2 with 10x lower amounts of halogen molecules, including CH3Cl and CH3Br
1% PAL 10x lower halogens	1% PAL of O2 with 10x lower amounts of halogen molecules, including CH3Cl and CH3Br
1% PAL 1e9x lower halogens	1% PAL of O2 with 1e9x lower amounts of halogen molecules, including CH3Cl and CH3Br
10% PAL 1D LBC and SRB	10% PAL of O2 with Kasting 1D model lower boundary conditions and absorption for HO2O and CO2 in the Schumann-Runge Bands included
1% PAL 1D LBC and SRB	1% PAL of O2 with Kasting 1D model lower boundary conditions and absorption for HO2O and CO2 in the Schumann-Runge Bands included
0.1% PAL 1D LBC and SRB	0.1% PAL of O2 with Kasting 1D model lower boundary conditions and absorption for HO2O and CO2 in the Schumann-Runge Bands included

Tidally locked exoplanet scenarios

Instructions on how to set up these cases are found in the Tidally_locked_exoplanets_folder.

Table 3

Simulation name	Description
TP-1e P19 PI	P19 spectrum, PI composition, tidally locked TP-1e, substellar point over Pacific Ocean
TP-1e P19 PI SPL	P19 spectrum, PI composition, tidally locked TP-1e, substellar point over Africa
TP-1e P19 PI noTL	P19 spectrum, PI composition, tidally locked TP-1e, not tidally locked (1 day rotation)
TP-1e P19 10% PAL	P19 spectrum, 10% PAL of O2, tidally locked TP-1e, substellar point over Pacific Ocean
TP-1e P19 1% PAL	P19 spectrum, 1% PAL of O2, tidally locked TP-1e, substellar point over Pacific Ocean
TP-1e P19 0.1% PAL	P19 spectrum, 0.1% PAL of O2, tidally locked TP-1e, substellar point over Pacific Ocean
TP-1e W21 PI	W21 spectrum, PI composition, tidally locked TP-1e, substellar point over Pacific Ocean
TP-1e W21 PI SPL	W21 spectrum, PI composition, tidally locked TP-1e, substellar point over Africa
TP-1e W21 PI noTL	W21 spectrum, PI composition, tidally locked TP-1e, not tidally locked (1 day rotation)
TP-1e W21 10% PAL	W21 spectrum, 10% PAL of O2, tidally locked TP-1e, substellar point over Pacific Ocean
TP-1e W21 1% PA	W21 spectrum, 1% PAL of O2, tidally locked TP-1e, substellar point over Pacific Ocean
TP-1e W21 0.1% PAL	W21 spectrum, 0.1% PAL of O2, tidally locked TP-1e, substellar point over Pacific Ocean
PCb PI	GJ551 MUSCLES spectrum, PI composition, tidally locked PC b, substellar point over Pacific Ocean
PCb PI SPL	GJ551 MUSCLES spectrum, PI composition, tidally locked PC b, substellar point over Africa
PCb 10% PAL	GJ551 MUSCLES spectrum, 10% PAL of O2, tidally locked PC b, substellar point over Pacific Ocean
PCb 1% PAL	GJ551 MUSCLES spectrum, 1% PAL of O2, tidally locked PC b, substellar point over Pacific Ocean
PCb 0.1% PAL	GJ551 MUSCLES spectrum, 0.1%PAL of O2, tidally locked PC b, substellar point over Pacific Ocean

The tidally locked simulations cover several cases for known M dwarf terrestrial exoplanets. The basic modifications include changing the rotation rate of the model, changing the radius and gravitational acceleration, and fixing the solar zenith angle (in order to fix the substellar point). The substellar point is placed either in the middle of the Pacific ocean at 180° longitude, or at 30° longitude in Africa. Additionally, depending on the exoplanet in question, the solar file will need to be changed and scaled to the irradiance that the planet recieves. The Stellar Wind and Irradiance Model (SWIM) has been developed for this purpose. The TRAPPIST-1e (TP-1e) simulations were originally started in 2020. In 2021, the Mega-MUSCLES spectrum (W21) became available, so this spectrum was introduced in order to compare the differences that arise in the simulations between the two spectra.

Other TRAPPIST-1 scenarios

Coming soon

Other exoplanet scenarios

Coming soon