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Runaway Greenhouse Effect in a Semigray Radiative-Convective Model

The effects of the nongray absorption (i.e., atmospheric opacity varying with wavelength) on the possible upper bound of the outgoing longwave radiation (OLR) emitted by a planetary atmosphere have been examined. This analysis is based on the semigray approach, which appears to be a reasonable compromise between the complexity of nongray models and the simplicity of the gray assumption (i.e., atmospheric absorption independent of wavelength). Atmospheric gases in semigray atmospheres make use of constant absorption coefficients in finite-width spectral bands. Here, such a semigray absorption is introduced in a one-dimensional (1D) radiative– convective model with a stratosphere in radiative equilibrium and a troposphere fully saturated with water vapor, which is the semigray gas. A single atmospheric window in the infrared spectrum has been assumed. In contrast to the single absolute limit of OLR found in gray atmospheres, semigray ones may also show a relative limit. This means that both finite and infinite runaway effects may arise in some semigray cases. Of particular importance is the finding of an entirely new branch of stable steady states that does not appear in gray atmospheres. This new multiple equilibrium is a consequence of the nongray absorption only. It is suspected that this new set of stable solutions has not been previously revealed in analyses of radiative–convective models since it does not appear for an atmosphere with nongray parameters similar to those for the earth’s current state

© Journal of the Atmospheric Sciences, 2002, vol. 59, núm. 19, p. 2801-2810

American Meteorological Society

Author: Pujol i Sagaró, Toni
North, Gerald R.
Date: 2002
Abstract: The effects of the nongray absorption (i.e., atmospheric opacity varying with wavelength) on the possible upper bound of the outgoing longwave radiation (OLR) emitted by a planetary atmosphere have been examined. This analysis is based on the semigray approach, which appears to be a reasonable compromise between the complexity of nongray models and the simplicity of the gray assumption (i.e., atmospheric absorption independent of wavelength). Atmospheric gases in semigray atmospheres make use of constant absorption coefficients in finite-width spectral bands. Here, such a semigray absorption is introduced in a one-dimensional (1D) radiative– convective model with a stratosphere in radiative equilibrium and a troposphere fully saturated with water vapor, which is the semigray gas. A single atmospheric window in the infrared spectrum has been assumed. In contrast to the single absolute limit of OLR found in gray atmospheres, semigray ones may also show a relative limit. This means that both finite and infinite runaway effects may arise in some semigray cases. Of particular importance is the finding of an entirely new branch of stable steady states that does not appear in gray atmospheres. This new multiple equilibrium is a consequence of the nongray absorption only. It is suspected that this new set of stable solutions has not been previously revealed in analyses of radiative–convective models since it does not appear for an atmosphere with nongray parameters similar to those for the earth’s current state
Format: application/pdf
ISSN: 0022-4928 (versió paper)
1520-0469 (versió electrònica)
Document access: http://hdl.handle.net/10256/7717
Language: eng
Publisher: American Meteorological Society
Collection: Reproducció digital del document publicat a: http://dx.doi.org/10.1175/1520-0469(2002)059<2801:RGEIAS>2.0.CO;2
Articles publicats (D-F)
Is part of: © Journal of the Atmospheric Sciences, 2002, vol. 59, núm. 19, p. 2801-2810
Rights: Tots els drets reservats
Subject: Efecte hivernacle (Meteorologia)
Greenhouse effect, Atmosphere
Radiació atmosfèrica
Atmospheric radiation
Gasos -- Absorció i adsorció
Gases -- Absorption and adsorption
Title: Runaway Greenhouse Effect in a Semigray Radiative-Convective Model
Type: info:eu-repo/semantics/article
Repository: DUGiDocs

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