Image:Atmospheric Transmission.png

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Description

Shows how the absorption and recycling of energy by the atmosphere is a defining characteristic of the greenhouse effect.

This figure shows the absorption bands in the Earth's atmosphere (middle panel) and the effect that this has on both solar radiation and upgoing thermal radiation (top panel). Individual absorption spectrum for major greenhouse gases plus Rayleigh scattering are shown in the lower panel.

Both the Earth and the Sun emit electromagnetic radiation (e.g. light) that closely follows a blackbody spectrum, and which can be predicted based solely on their respective temperatures. For the sun, these emissions peak in the visible region and correspond to a temperature of ~5500 K. Emissions from the Earth vary following variations in temperature across different locations and altitudes, but always peak in the infrared.

The position and number of absorption bands are determined by the chemical properties of the gases present. In the present atmosphere, water vapor is the most significant of these greenhouse gases, followed by carbon dioxide and various other minor greenhouse gases. In addition, Rayleigh scattering, the physical process that makes the sky blue, also disperses some incoming sunlight. Collectively these processes capture and redistribute 25-30% of the energy in direct sunlight passing through the atmosphere. By contrast, the greenhouse gases capture 70-85% of the energy in upgoing thermal radiation emitted from the Earth surface.

Data sources and notes

The data used for these figures is based primarily on Spectral Calculator of GATS, Inc. which implements the LINEPAK system of calculating absorption spectra (Gordley et al. 1994) from the HITRAN2004 (Rothman et al. 2004) spectroscopic database. To aid presentation, the absorption spectra were smoothed. Features with a bandwidth narrower than 0.5% of their wavelength may be obscured.

Calculations were done on the assumption of direct vertical transmission through an atmosphere with gas concentrations representative of modern day averages. In particular, absorption would be greater for radiation traveling obliquely through the atmosphere as it would encounter more gas.

The total scattering and absorption curve includes only the components indicated in the lower panel. These represent the vast majority of absorption contributing to the greenhouse effect and follow the treatment of Peixoto and Oort (1992), but other minor species such as carbon monoxide, nitric oxide and chloroflourocarbons (CFCs) have been omitted. Also omitted was scattering due to aerosols and other sources besides Rayleigh scattering.

The peaks in the blackbody spectra were adjusted to have the same height for ease in presentation.

Copyright

This figure was prepared by Robert A. Rohde for the Global Warming Art project.

Image from Global Warming Art

This image is an original work created for Global Warming Art.

Permission is granted to copy, distribute and/or modify this image under either:

• The GNU Free Documentation License Version 1.2; with no Invariant Sections, Front-Cover Texts, or Back-Cover Texts.
• The Creative Commons Attribution-NonCommercial-ShareAlike License Version 2.5

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Please refer to the image description page on Global Warming Art for more information

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 only as published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled " Text of the GNU Free Documentation License." Català | English | Español | Français | 日本語 | Polski | Português | Русский | Tiếng Việt | ‪中文(简体)‬ | ‪中文(繁體)‬ | +/-

References

• Gordley, Larry L., Benjamin T. Marshall, Allen D. Chu (1994). "LINEPAK: Algorithms for modeling spectral transmittance and radiance". Journal of Quantitative Spectroscopy & Radiative Transfer 52 (5): 563-580.
• L.S. Rothman, D. Jacquemart, A. Barbe, D. Chris Benner, M. Birk, L.R. Brown, M.R. Carleer, C. Chackerian Jr., K. Chance, L.H. Coudert, V. Dana, V.M. Devi, J.-M. Flaud, R.R. Gamache, A. Goldman, J.-M. Hartmann, K.W. Jucks, A.G. Maki, J.-Y. Mandin, S.T. Massie, J. Orphal, A. Perrin, C.P. Rinsland, M.A.H. Smith, J. Tennyson, R.N. Tolchenov, R.A. Toth, J. Vander Auwera, P. Varanasi, G. Wagner (2004). "The HITRAN 2004 molecular spectroscopic database". Journal of Quantitative Spectroscopy & Radiative Transfer 96: 139-204.
• Peixoto, Jose P. and Abraham H. Oort (1992). Physics of Climate. Springer.

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