On Nov 27, 3:11 am, "Raymond W. Arritt" <[EMAIL PROTECTED]> wrote: > Alastair wrote: > > I (and Newton) say that warming is caused by absorption. After WWII > > they found that the lines were narrower at high altitude, but the > > radiation has all been absorbed well before it reaches that height. > > In fact it is nearly all absorbed in the first 30m. John Tyndall > > reckoned that 10% was absorbed in the within the first 6 feet. > > What happens to the energy that corresponds to the absorbed radiation? > Since energy cannot be created or destroyed (leaving relativistic > effects aside here), do the lowest few tens of meters continue to heat > indefinitely?
The simple answer is yes. You can see this most obviously on Venus where the surface heated up until it melted. What happened then was that clouds formed and cut off the initiating solar radiation. On Earth the most of the surface is already molten, and the average cloud cover has makes the incoming solar radiation match the outgoing longwave radiation. On Mars conditions are different and dust storm form long before the surface melts. These intermittent dust storms provide the cooling to Mars that on Earth happens due to "permanent" by water clouds. Of course everyone thinks that it is the thick CO2 atmosphere that gives Venus its runaway greenhouse, but the with the standard model the maximum surface temperature is twice the effective temperature. For Venus that is widely exceeded. This is a known problem; see Goody and Walker's Atmospheres 1972. On Earth, this would solve the Faint Young Sun problem. See this link for a description of it. http://arjournals.annualreviews.org/doi/abs/10.1146/annurev.aa.32.090194.000503 Of course convection is also acting, and that is claimed to save the model, there is very little convection on Venus or Mars. > > There are two things happening. There is the greenhouse warming at > > the surface of the atmosphere, and there is OLR at the top of the > > atmosphere. The OLR has to balance the ISR but it cannot change > > because it is coming from the mesosphere which does not respond to the > > surface temperature. (I am leaving a lot out, but you should be able > > to see the picture.) > > Where does the OLR come from, if (as you state) all the outgoing > radiation from the surface is absorbed in the lowest few tens of meters? A good point! My previous description was an over simplification. Greenhouse gases both absorb and emit. Both are quantum mechanical effects and so are not simple but I will try to explain without writing a text book. So I will ignore water vapour which complicates things by condensing. In the middle atmosphere all the CO2 molecules are at the same temperature so on average they are all radiating with the same strength. And thus you have a situation where Kirchoff's Law is obeyed and absorption equals emission. At the TOA there are no molecules in space radiating in so there is a net loss of radiation out to space and this is where OLR is generated. (Of course you knew that already.) At the base of the atmosphere, the surface radiates blackbody radiation, and the intensity in the CO2 bands depends on the surface temperature through Planck's blackbody function B(T). Einstein showed that the greenhouse gas will also emit radiation according to B(T) so it would seem that once the air equals the surface temperature then all absorption will cease. So de Saussure's hot box should not work. http://www.solarcooking.org/saussure.htm But the T for the CO2 vibrational emission is the vibrational temperature not the kinetic temperature. Tvib is much lower than T for CO2 because its vibrations are "frozen out". So it is all of the net radiation which is absorbed in the first 30 m, not all of the all outgoing radiation :-) HTH, Cheers, Alastair. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups Global Change ("globalchange") newsgroup. Global Change is a public, moderated venue for discussion of science, technology, economics and policy dimensions of global environmental change. Posts will be admitted to the list if and only if any moderator finds the submission to be constructive and/or interesting, on topic, and not gratuitously rude. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/globalchange -~----------~----~----~----~------~----~------~--~---
