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

Yang, Jun and Leconte, Jérémy and Wolf, Eric T. and Goldblatt, Colin and Feldl, Nicole and Merlis, Timothy M. and Wang, Yuwei and Koll, Daniel D. B. and Wang, Feng and Forget, François and Abbot, Dorian S. (2016) Differences in Water Vapor Radiative Transfer among 1D Models Can Significantly Affect the Inner Edge of the Habitable Zone. Astrophysical Journal, 826 (2). Art. No. 222. ISSN 0004-637X. http://resolver.caltech.edu/CaltechAUTHORS:20161003-082759999

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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.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.3847/0004-637X/826/2/222DOIArticle
http://iopscience.iop.org/article/10.3847/0004-637X/826/2/222/metaPublisherArticle
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.
Subject Keywords:astrobiology; methods: numerical; planets and satellites: atmospheres; planets and satellites: general; planets and satellites: terrestrial planets; radiative transfer
Record Number:CaltechAUTHORS:20161003-082759999
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20161003-082759999
Official Citation:Jun Yang et al 2016 ApJ 826 222
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:70742
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:03 Oct 2016 17:03
Last Modified:03 Oct 2016 17:03

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