DOI: 10.5281/zenodo.17187196
title: Model Outputs and Spectra for "Limb Asymmetries on WASP-39b: A Multi-GCM Comparison of Chemistry, Clouds, and Hazes"

description: This Zenodo archive contains data supporting the publication “Limb Asymmetries on WASP-39b: A Multi-GCM Comparison of Chemistry, Clouds, and Hazes” by Steinrueck, Savel, Christie et al. (2025). 

Publication abstract

With JWST, observing separate spectra of the morning and evening limbs of hot Jupiters has finally become a reality. The first such observation was reported for WASP-39b, where the evening terminator was observed to have a larger transit radius by about 400 ppm and a stronger 4.3 µm CO2 feature than the morning terminator. Multiple factors, including temperature differences, photo/thermochemistry, clouds and hazes, could cause such limb asymmetries. To interpret these new limb asymmetry observations, a detailed understanding of how the relevant processes affect morning and evening spectra grounded in forward models is needed. Focusing on WASP-39b, we compare simulations from five different general circulation models (GCMs), including one simulating disequilibrium thermochemistry and one with cloud radiative feedback, to the recent WASP-39b limb asymmetry observations. We also post-process the temperature structures of all simulations with a 2D photochemical model and one simulation with a cloud microphysics model. Although the temperatures predicted by the different models vary considerably, the models are remarkably consistent in their predicted morning--evening temperature differences. Several equilibrium-chemistry simulations predict strong methane features in the morning spectrum, not seen in the observations. When including disequilibrium processes, horizontal transport homogenizes methane, and these methane features disappear. However, even after including photochemistry and clouds, our models still cannot reproduce the observed ~2000 ppm asymmetry in the CO2 feature. A combination of factors, such as varying metallicity and unexplored parameters in cloud models, may explain the discrepancy, emphasizing the need for future models integrating cloud microphysics and feedback across a broader parameter space.

Content Description

Contents

The folder “Vulcan2DInput” contains the 2D pressure-temperature and velocity profiles that were used as input for 2D Vulcan. (See below for a more detailed description of files.)

The folder “spectra” contains the spectra presented in the publication.

PT.ipynb is a Jupyter notebook for reproducing Figures 1 (temperature profiles at terminator) and  2 (temperature profiles at substellar and anti stellar point) in the paper.

VelProf.ipynb reproduces Figures 18 (vertical profiles of zonal velocity).

Spectra.ipynb reproduces Figures 3, 8, 9 and 14. Note that in order to work, this script needs the observational data from Espinoza et al. (2024) in the form of the file catwoman_res100_priorlds.txt, which can be downloaded from https://github.com/nespinoza/wasp39-terminators in the folder “figure3” (permalink: https://github.com/nespinoza/wasp39-terminators/blob/57587796023fee9051121ea17d435f0ad6852589/figure3/catwoman_res100_priorlds.txt). The correct citation for the observational data is:Espinoza, N., Steinrueck, M.E., Kirk, J. et al. (2024): Inhomogeneous terminators on the exoplanet WASP-39 b. Nature 632, 1017–1020. https://doi.org/10.1038/s41586-024-07768-4

Description of files in Vulcan2DInput

Filenames: The first part of each filename describes the model that contributed the model. For each model, there are two files, one ending in “RMSwind”, describing the velocities in the simulation, and one ending in “TP”, describing the temperature structure. 

Each file contains three lines of header. The first line in the header includes the number of longitudes included, then a list of the values of the longitudes, with a longitude of zero referring to the substellar point. The second line specifies the units of the columns. The third line lists the columns individually.

The first column of each “TP” file contains pressure, the other columns contain the temperatures at each of the longitudes included.

The first column of each “RMSwind” file contains pressure, the next N_lon columns contain zonal (=longitudinal) velocities at the longitudes listed in the header, where N_lon is the number of longitudes included, and the final N_lon columns contain the vertical velocities.

All quantities (temperature, zonal velocity, vertical velocity) were averaged latitudinally from -30 degrees to +30 degrees latitude. For temperature and zonal velocities, the mean was used. Zonal (=longitudinal) velocities are reported as positive for eastward velocities. For vertical velocities, the root-mean-square was used.

Description of files in spectra

For each simulation, there is a separate file for the morning and evening spectrum each. The first column contains the wavelength in micrometers, the second column contains the transit depth in percent. When calculating the transit depths separately for the morning and evening terminator, the morning or evening side was mirrored onto the other half of the planet for the 3D ray-striking radiative transfer calculation, as described in section 2.5 in Steinrueck, Savel, Christie et al. When comparing to the limb depths reported by Espinoza et al. (2024) derived with catwoman, these transit depths have to be divided by a factor of two, as the limb depths correspond to the area of a semi-circle rather than a full circle.

For the spectra including photochemistry, “B1” in the filenames corresponds to the “Full limb” post-processing and “B2” corresponds to the “Jet” post-processing.

For the figures in Steinrueck et al. (2025), the spectra were shifted up or down to provide the best match to the full-transit transmission spectrum calculated using a least-squares minimization. See Section 3.3 in the paper or Spectra.ipynb for more details.

Attribution

Please cite Steinrueck, Christie, Savel et al. (2025) as well as the Zenodo record when using the model outputs or spectra included in this repository.