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To: ETL
Ok folks, another thinking cap question: I was taught that gases do absorb energy. See the below reference. Now, what does the gas do with the absorbed energy? I was taught that it did not increase the temp of the gas but that the electrons were stepped up to another level. Eventually the gas molecule would want to settle down and would release the energy as a photon again? If random, half would be release back to outer space and half transmitted to earth. Ok, the below says CO2 is a good absorber of infrared energy but NOTE THAT THE STAEMENT STOPS THERE. What happens to that absorbed energy.? My mind says that half goes down to earth and half goes to space. Do the “models” assume it all goes back to earth? It is more complex than this as I remember pigments (not gases) absorb higher spectrum and release lower spectrum.

Greenhouse Gas Absorption Spectrum
http://www.meteor.iastate.edu/gccourse/forcing/spectrum.html
Figure 4 gives the amount of energy absorbed by greenhouse gases in various wavelength regions, from ultraviolet radiation on the left, to visible light in the middle, to infrared radiation on the right.

The CFCs are not plotted here but will be considered separately. For each gas is given a plot of the absorptance of the gas, ranging from 0 to 1, for each wavelength.

As an example, if we look at the plot for oxygen and ozone, we see that the absorption is very high in the ultraviolet region but essentially zero in the visible and infrared regions, except for isolated peaks. We interpret this to mean that this gas absorbs essentially all radiation in the ultraviolet but is transparent in the visible and mostly transparent in infrared portions of the spectrum. This gas then is responsible for shielding earth-based biological systems from lethal ultraviolet radiation, radiation with wavelengths less than 0.3 micrometers (or 300 nanometers), but allows visible light and infrared radiation to pass through without much absorption.

Other gases have much different absorption properties. Methane (CH4), for example, has a couple of very small wavelength regions in which it absorbs strongly and these occur at about 3.5 and 8 microns, which are in the infrared region. Nitrous oxide, N2O, having peaks at about 5 and 8 microns, absorbs in fairly narrow wavelength ranges.

Carbon dioxide has a more complex absorption spectrum with isolated peaks at about 2.6 and 4 microns and a shoulder, or complete blockout, of infrared radiation beyond about 13 microns. From this we see that carbon dioxide is a very strong absorber of infrared radiation. The plot for water vapor shows an absorption spectrum more complex even than carbon dioxide, with numerous broad peaks in the infrared region between 0.8 and 10 microns.

The total spectrum of all atmospheric gases is given in the bottom plot. This shows a “window” between 0.3 and 0.8 microns (the visible window), which allows solar radiation (without the lethal UV component) to reach the earth's surface. “Earth radiation”, the upwelling infrared radiation emitted by the earth's surface, has a maximum near 10 microns. The total atmosphere plot shows that a narrow window (except for an oxygen spike) exists in the range of wavelengths near 10 microns.

41 posted on 02/15/2010 7:44:01 AM PST by PeterPrinciple ( Seeking the truth here folks.)
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To: PeterPrinciple
If we look at that graph...

We see that water vapor not only absorbs more wavelengths, those wavelengths are shorter than those absorbed by CO2. Shorter wavelengths have higher energy than longer wavelengths. Thus H20 absorbs much more energy than does CO2. These higher energies are then converted into kinetic energy; heat.

44 posted on 02/15/2010 7:54:06 AM PST by Redcloak (Messin' up threads since 1998)
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