Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published August 1, 2016 | Published
Journal Article Open

Differences in Water Vapor Radiative Transfer among 1D Models Can Significantly Affect the Inner Edge of the Habitable Zone

Abstract

An accurate estimate of the inner edge of the habitable zone is critical for determining which exoplanets are potentially habitable and for designing future telescopes to observe them. Here, we explore differences in estimating the inner edge among seven one-dimensional radiative transfer models: two line-by-line codes (SMART and LBLRTM) as well as five band codes (CAM3, CAM4_Wolf, LMDG, SBDART, and AM2) that are currently being used in global climate models. We compare radiative fluxes and spectra in clear-sky conditions around G and M stars, with fixed moist adiabatic profiles for surface temperatures from 250 to 360 K. We find that divergences among the models arise mainly from large uncertainties in water vapor absorption in the window region (10 μm) and in the region between 0.2 and 1.5 μm. Differences in outgoing longwave radiation increase with surface temperature and reach 10–20 W m^(−2); differences in shortwave reach up to 60 W m^(−2), especially at the surface and in the troposphere, and are larger for an M-dwarf spectrum than a solar spectrum. Differences between the two line-by-line models are significant, although smaller than among the band models. Our results imply that the uncertainty in estimating the insolation threshold of the inner edge (the runaway greenhouse limit) due only to clear-sky radiative transfer is ≈10% of modern Earth's solar constant (i.e., ≈34 W m^(−2) in global mean) among band models and ≈3% between the two line-by-line models. These comparisons show that future work is needed that focuses on improving water vapor absorption coefficients in both shortwave and longwave, as well as on increasing the resolution of stellar spectra in broadband models.

Additional Information

© 2016 American Astronomical Society. Received 2016 March 31; revised 2016 May 23; accepted 2016 May 26; published 2016 August 2. We thank the anonymous reviewer for her/his helpful comments and suggestions that greatly improved the article. We are grateful to Robin Wordsworth for insightful discussions, and to Jonah Bloch-Johnson and Xiaoxiao Tan for their help in radiative transfer calculations. We thank Rodrigo Caballero for maintaining CliMT, which we used in the project. Software: SBDART, AM2 (1D), CAM3 (1D), CAM4_Wolf (1D), LMDG (1D), SMART, LBLRTM.

Attached Files

Published - apj_826_2_222.pdf

Files

apj_826_2_222.pdf
Files (2.3 MB)
Name Size Download all
md5:8565787760652ea8f81ff4a6308b5f90
2.3 MB Preview Download

Additional details

Created:
August 22, 2023
Modified:
October 20, 2023