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Viewing Single Post From: The giant space ship example  

Chris HoStuart  Dec 11 2011, 06:38 AM 
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The point is that CO2 is not a grey gas; accurate modeling of CO2 will require calculation of frequency dependent k values.
Venus is a good example. I used these parameters in the 8 available input places. Radius: 6052 (a tad less than Earth) Gravity: 8.9 (a tad less that Earth) Surface temperature: 464C (very hot!) Surface air pressure: 92 atm (very high pressure) Cp: 0.8501 (check out the references at the "readme" sheet; one of them gives Cp and R for different planets gamma: 1.2857 (using gamma = 1/(1Cp/R) and R = 0.1889) Lapse rate: I just used the DALR calculated, which is 10.47 k: 473 The choice of "k" is really only picking the number that happens to give the thermal emission to space at the correct value of 184.2 W/m^2 As expected, this is a higher k value than for Earth. Beyond that we can't say much, because neither planet has a grey atmosphere. The values for the greenhouse effect magnitude are as expected, which is no surprise. The "k" value was chosen only on the basis of getting those results!
Yes; that is an interesting consequence of the fixed lapse rate assumption. If the lapse rate is fixed all the way up the atmosphere, then the altitude at which you get a temperature of absolute zero depends only on lapse rate and surface temperature. Pressure makes no difference. Really. What happens with higher pressures is that the gas is just more dense. Maximum altitude stays unchanged. Version 2 is going to remove the fixed lapse rate assumption, by identifying a tropopause and applying radiative equilibrium above that point. I don't expect it to make much difference to the magnitude of the greenhouse effect in most cases; but I'll have to see. It will be a more realistic model of the atmosphere; but the tropopause height I calculate won't be particularly accurate. I haven't attempted to do the moist adiabat, let alone model the environmental lapse rate. In reality, the troposphere on Earth tends to have lapse rates that are slightly unstable to convection; and there's a usually a point within the troposphere where the atmosphere has dried out and the dry adiabiat is the stable case up until the tropopause. 
The giant space ship example · Physical theory for climate 