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Post by nonentropic on Nov 13, 2009 3:36:41 GMT
I would have thought that with such fantastic satellite technology we would know the temperature record of mars to a micron as we do on earth also from such instruments.
The other thing that stuns me is we have put up as an example of the effects of CO2 on climate Venus. It does not rotate and we are constantly reminded that it is the model of what will happen to Earth if the CO2 level rises. That is you will have molten lead in the streets. Does anyone know the temperature of the cold side, or more interesting the average temperature of the Planet? I suspect it will be a little less spectacular than suggested.
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Post by spaceman on Nov 13, 2009 3:52:04 GMT
Well we do have 390/w/m^2 leaving it's over a larger surface area measuring 240w/m^2. Do the math. It's 390 w/m^2 spread out over increasing area as space is approached. What time interval are we talking about?
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Post by socold on Nov 13, 2009 19:45:51 GMT
I would have thought that with such fantastic satellite technology we would know the temperature record of mars to a micron as we do on earth also from such instruments. The problem is the temperature of Mars varies from night to day and season to season so much that it's hard to put a precise figure on average temperature. We don't even know the absolute temperature of Earth very well, only that it's about 15C. Same problem, but not as bad as with Mars. The surface temperature of Venus over 400 degrees C. That level of warming won't happen to Earth even if co2 does rise. Something crazy happened on Venus that let it's greenhouse effect runaway. It won't happen on Earth, the best we'll do is warm Earth up a lot but nothing like hundreds of degrees.
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Post by socold on Nov 13, 2009 19:50:02 GMT
socold, What happened to the run a way increase in heat? Mars atmosphere is 95% co2. With that much co2 it is pretty easy to calculate the amount of retained heat based on the model they did for earth minus pressure and watts/m^2. Mars has a far less dense atmosphere than Earth, so that 95% co2 is only about 12 times the co2 that Earth has. The pressure difference affects absorption so no easy comparison can be made. I agree, the number will be about somewhere.
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Post by socold on Nov 13, 2009 19:56:43 GMT
There are a number of different values for the surface temperature of Mars. I kept finding new ones when I googled around. Who is right? After seeing how much variation there is between night and day and across the year I gave up because it's clear noone can pin down the actual surface temperature average with any certainty due to such variation. Given that the greenhouse effect would be significantly smaller than on Earth, it's probably within that uncertainty. Thank you SoCold. But another question. Why would the greenhouse effect be significantly smaller than on earth? I know the pressure is less and am not learned enough to extrapolate that pressure diff to the 15X co2. I have read it's a few degrees F, not great sources they just mention it in passing, but that's all I have found. While there's more co2 in the martian atmosphere there is far less water vapor so I can understand why it would be less than on Earth. If the average temp of the atmosphere and the surface is uncertain then the difference between them would be uncertain too
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Post by kiwistonewall on Nov 14, 2009 9:01:35 GMT
(From Goody & Yung) As I have maintained, Oxygen and Nitrogen (in fact all the atmopheric gases except Argon etc) have a background thermal absorbance/emission from collisions: Quote: pg115 "a homonuclear diatomic molecule such as oxygen or Nitrogen, that has no dipole moment in an isolated state, may have a dipole moment induced in it by a colliding molecule, in which case dipole transitions may occur during the short period occupied by the collision" and "collision-induced spectra and dimers or polymers, have some relevance to atmospheric calculations" Collisions induced will follow the boltzmann distribution and is reflected in the low intensity, but standard blackbody shape. The 10-20% of atmospheric absorbance outside the spectral lines can be attributed at least partly to this effect, though some of that additional absorbance will be due to dust and aerosols. But because this low level absorbance (10-20%) operates across the entire Earth thermal spectrum, even in the so called IR window, the magnitude of this contribution to the greenhouse effect is high. Oxygen and Nitrogen do have IR absorption when (O2)2 and (N2)2 and maybe O2-N2 are formed (Quadrapoles). These are strongly seen at higher pressures, but will form at lower pressures. The main Oxygen and Nitrogen (dimer) absorption is at 6.42 and 4.29 microns. The 6.42 band is right slap in the middle of the Water band, and 4.29 in one of the CO2 bands. All this is discussed in Atmospheric radiation: theoretical basis By Richard M. Goody, Y. L. Yung Link to relevant discussion is here: books.google.com.au/books?id=Ji0vfj4MMH0C&pg=PA116&lpg=PA116&dq=Oxygen+molecule+Quadrapole&source=bl&ots=7SiSU421ag&sig=LR2-JGvbz_Vh-t5dbrbYYb-yMy8&hl=en&ei=JGP-SojDHo-msgP-rPSHCw&sa=X&oi=book_result&ct=result&resnum=1&ved=0CAgQ6AEwADgK#v=onepage&q=&f=falseAs I have stated before, ALL matter radiates thermal energy. Goody & Yung also state the need to consider O2 & N2 for accurate atmospheric heat balance. The addition absorbance is what reduces transmittance in the atmosphere: Even in the best IR window region, something is still blocking 10% (and mostly 20-30%) this can only be the Atmosphere as a whole, plus any minor effects from Aerosols & dust)
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Post by kiwistonewall on Nov 14, 2009 9:24:59 GMT
Of course, it is absolutely immaterial WHAT causes the 10-30% aborbance across the Earth thermal Spectrum. (That is, the failure of transmittance to be 100%) Whatever it is, it is a major contribution to the greenhouse effect, as it operates across the entire bandwidth.
It may be collisions of molecules, dust or aerosols, but that is entirely moot. The point will be obvious to all who understand integration.
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Post by steve on Nov 16, 2009 11:23:54 GMT
Well we do have 390/w/m^2 leaving it's over a larger surface area measuring 240w/m^2. Do the math. It's 390 w/m^2 spread out over increasing area as space is approached. What time interval are we talking about? Watts are joules per second. So we are talking about a time interval of every second. We don't have 390W/m^2 leaving. Calculate the surface area of a sphere of 6700km (radius of earth's surface) then one of a sphere of 6900km (approx height of a satellite measuring the radiation budget). Venus doesn't really have a cold side. It's spectacularly hot all over.
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Post by steve on Nov 16, 2009 11:45:18 GMT
As was stated earlier, even in the "window", water vapour has a continuum-like spectrum which can account for much of the absorption in this window.
It is an interesting finding, Kiwistonewall, and much appreciated. But it is more relevant to the discussion between you and the dearly departed Radiant who appeared to hold that a O2-N2 atmosphere would be super transmitting. I note that the measurements they describe are done at 10 bar and 60 bar - the pressure being important because it increases the frequency of the collisions that produce the lines.
But the position you seemed to hold before was that the spectrum was "grey". The important point for the "greenhouse effect" is that the window exists at all. Whether it is 10% or 30%, it still leaves more than 70% of radiation in parts of the spectrum to be affected by the increasing levels of CO2 which, even above half of the atmosphere and most of the water vapour, will readily absorb most of the radiation around its spectral lines.
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