The MODTRAN web user interface allows you to see radiative fluxes given a temperature profile. The temperatures are an input, not an output.
No one denies that the atmosphere becomes opaque at absorption bands as the absorbing constituent increases. In the tool exposed on the web, though, and in MODTRAN standing alone, the feedback to temperature is absent. So it doesn't answer the question. Once again, Bill, you are (at best) assuming you understand things you don't. about the project: I can take no credit for this project. (Remarkably, David's young son Jeremy did the web interface, I think at the age of 12, building on some work of David's to simplify setting up the runs for his undergrad classes.) MODTRAN itself is a product of the USAF, the result of many years of professional effort, though. For some reason some patents apply, which I find not especially satisfactpry as a taxpayer, but taht's a bit beside the point. about Venus: Here is an interesting commentary from http://www.realclimate.org/index.php/archives/2006/04/lessons-from-venus/ by Ray Pierrehumbert (response to comment 10) ===> logarithmic behavior of CO2 in Earth's atmosphere only applies over a limited (but rather extensive) range of concentrations. At very low concentrations (say, around 1 ppm) bands are unsaturated and OLR becomes more sensitive to CO2 than in the logarithmic range. At sufficiently high concentrations (say, when you start to get around 10% or 20% of CO2 in the atmosphere) the absorption starts to be dominated by weak bands that have a different probability distribution than the bands that dominate in the present climate; this again starts to lead to an increase in sensitivity. Radiative transfer is complicated because of the complex line structure of greenhouse gases, but for a long time I have been looking for a simple, accessible explanation of the typical logarithmic behavior. I'm writing that section of my climate book now (check Chapter 4 of The Climate Book in a few months). As far as I can tell, the simplest way to put it is like this: CO2 opacity for the present Earth is dominated by the 15 micron band group. The envelope of the absorption strength in this group tails off roughly exponentially from the center of the group, once the lines are broad enough to overlap significantly within each sub-band of the interval, and the resulting probability distribution of absorption can be shown to give rise to the logarithmic behavior. However, the exponential envelope is only approximate, and only extends a certain distance out from 15 microns, so once you put in enough CO2 you get out of the logarithmic range. Hence the answer to your question, roughly, is that it depends both on pressure/temperature broadening and on CO2 concentration. To get a logarithmic behavior, you need enough pressure or temperature to make the lines broad enough to start overlapping, but if you put in too much CO2, you make the overall width of the principal absorption region (that's not the line width!) wide enough that you get out into a different shape of envelope, and lose the logarithmic behavior. <=== Of course, the main article and many of the other commentaries are very interesting. mt --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
