The warming effect of CO2 is expressed by the ditch in the spectrum between wave numbers 550 and 800, with the bottom of the ditch associated with the emission temperature 220 K occurring in the tropopause. This is the minimum temperature of the atmosphere and thus gives maximal warming effect of CO2. Running Modtran with different concentration of CO2 from 50 ppm to 1000 ppm puts the bottom of the ditch at 220 K with the central resonance at 667 climbing to higher temperature reflecting emission from the stratosphere.
Modtran/IRIS translates a line spectrum to a continuous spectrum with the CO2 warming effect expressed as the area of the ditch in the spectrum between 550 - 800. The area depends on the bottom of the ditch anchored at 220 K for CO2 concentrations larger than 50 ppm, and on the width which is slightly increasing with increasing concentrations. The warming effect of doubled CO2 from 300 ppm then comes out to be 3.7 W/m2, which serves as the starting point of CO2 alarmism. This effect is not directly measured but comes from a model of line broadening in a translation of a line spectrum to a continuous spectrum.
In an upcoming post I will scrutinize the line broadening model. To prepare, note that the emission altitude and thus temperature is determined by the fact that the atmosphere above that altitude is essentially transparent to the chosen wave number. Increasing CO2 concentration will then mean increasing altitude and then cooling above the tropopause as seen for 667. The key question of OLR can thus be reduced the tractable problem of transparency at sufficient altitude without resolving the complex heat transfer within the atmosphere. This makes it possible to decode fabrication of artificial warming if present.
Inlägg
Here is a clear demonstration on the unreliability of the HITRAN - MODTRAN data that, rearranged, give an optical depth of about 100q (q is the mixture ratio in ppm) for the wavelength of 15 microns and the CO2 at zero height in the terrestrial atmosphere.
SvaraRaderaThat is τ0 = 38000: simply huge!
The optical depth is proportional to the pressure and varies with the height as
τ0 = τ0exp(-z/H)
with H of approximately 8 km.
With these values the Earth's atmosphere should be:
- completely opaque for 0 < z < 72 km
- gray for 72 < z < 84 km
- transparent for z > 84 km
This is very absurd for the Earth where the atmosphere is transparent above 16 km.
The HITRAN - MODTRAN data on the CO2cross sections should be reduced to at least 2/10000.
Michael
Maybe I do not understand the spectralcalc version of Modtran but if I put in CO2 and wavelengths 13 to 16 micron it gives 4 peaks at 13.4, 13.9, 14.7, & 15.4 where as if I put in H2O there is one peak at 14.9 micron.
SvaraRaderaThere is no doubt that there is an overlap of radiation absorption between H2O & CO2 in the wavelength around 14.8 micron which has been the measured to be the peak for CO2 and that is why it is not used for CO2 detection in distant stars and planets. However, all the absorption spectra, I am aware of, has a single peak for CO2 and multiple peaks for H2O in the range 13-16 micron. The broadening of the absorption of CO2 by additional concentration(or partial pressure) should not be noticeable whereas this should be be a distinguishing feature of H2O.
One has to wonder if Spectralcalc or Modtran has mixed up these gases.
You have found something that few bother to look at and just accept because a) the originators of such calculation methods do not list their assumptions, calculation methods or computer code b)very few have the necessary understanding of the technology involved or the mathematical and computer skills to detect problems, and C) there is a general acceptance particularly by people who lack technical competence to accept the written word of others they think are more skilled (that is a failure of peer review)
I have come across many errors in computer programs particularly arising from the USA due to a) unclear and wrong assumptions b) lack of understanding of statistics and treatment of errors and d) lack of understanding of dimensions and wrong use of units -many in USA still use modified imperial units and do not know how to correctly convert d) poor computer code, and finally d) lack of real world experience in measurement, analyses and process control.
The agreement in the diagram between the measured curve according to IRIS and the calculated one according to Modtran is fairly good. But how is the difference between the curves at the ATM Window explained?
SvaraRaderaBoth are similarly computed from spectral input from Hitran/IRIS which explains the close similarity. Yes, the drop in the Modtran results in the ATM window is the only notable difference. It probably reflects Hitran data with some absorptivity even in the window.
SvaraRaderaPS As far as I understand, IRIS singles out a gas line spectrum from a continuous spectrum, reflecting the line spectrum of Hitran, and the computations involve translating line spectra from IRIS/Hitran to a continuous spectrum using in particular a model for line broadening which thus is the crucial part. With the same line broadening model IRIS and Hitran gives very similar results.
SvaraRadera