Guest Post by Willis Eschenbach
I’ve been messing about with the “Modtran” online calculator for atmospheric absorption. It’s called “Modtran” because it is a MODerate resolution program to calculate atmospheric infrared absorption written in ForTRAN, which calculates the result for each 1 cm-1 wide band of the wavenumber across the spectrum. Not quite a “line-by-line” calculation, but close. Here’s a sample of the input page:
Figure 1. User input page for the Modtran online calculation for infrared absorption. Left side is user input. Upper right graph shows absorption as a function of frequency. The lower right graph shows the GHG concentrations, pressure, and temperature, as a function of altitude. See here for an overview of the model. Click to enlarge
This shows the situation during the subarctic summer, with no clouds or rain.
Along the way, I ran into a curious mystery, one for which I have no answer.
Here’s the peculiarity I found. I decided to see what Modtran had to say about the “instantaneous forcing”. This is the forcing immediately after a change in e.g. CO2 or other greenhouse gas. In Table 1 of “Efficacy of Climate Forcings” , James Hansen et al. say that the instantaneous forcing from a doubling of CO2 is 4.52 W/m2.
So I tested that claim with Modtran using a variety of different locations, with different combinations of clear skies, cloud, and rain. I started by testing every few hundred PPMV increase, to see if the results were linear with the log (to the base 2) of the change in CO2. Finding that they were perfectly linear, I then tested each situation using 375 ppmv, doubled CO2 (750 ppmv) and two doublings of CO2 (1500 ppmv). I noted the absorption at each level, and compared that to the logarithm (base 2) of CO2. That let me calculate the forcing, which is typically given as the change in forcing for a doubling of CO2. Using Modtran, I get the following results:
Figure 2. Instantaneous forcing calculated by Modtran for different scenarios.
Now, this has the expected form, in that the forcing is highest at the equator and is lowest at the poles. The addition of either rain or clouds reduces the forcing, again as we’d expect, except during subarctic winter when some kinds of clouds increase the forcing slightly.
So the mystery is, according to Modtran, the absolute maximum instantaneous forcing from a doubling of CO2 is 3.2 W/m2 in the clear-sky tropics. I can’t find any combination of locations and weather that gives a larger value for the instantaneous forcing than that. And the minimum value I can find is subarctic winter plus cirrus, at 1.57 W/m2. I can’t find any combination giving less than that, although there may be one.
As a result, according to Modtran the planetary average instantaneous forcing from CO2 doubling cannot be any more than 3.2 W/m2, and is likely on the order of 2.4 W/m2 or so … but according to Hansen et al., the real answer is nearly double that, 4.5 W/m2.
So the mystery is, why is the accepted value for instantaneous forcing nearly twice what Modtran says?
Note that the answer to the mystery is not “feedbacks”, because we’re looking at instantaneous forcing, before any response by the system or any possible feedbacks.
All suggestions welcome, except those that are anatomically improbable …
w.
DATA: Excel spreadsheet here. You don’t need it, though. For any situation, simply use Modtran successively for two CO2 values where one CO2 value is double the other, and note the difference in the calculated upwelling radiation. This is the instantaneous climate sensitivity for that situation.
THE USUAL: If you disagree with me or someone else, in your comment please quote the exact words that you disagree with. This lets everyone know your exact subject of disagreement.
NOTE: I see as I finish this that they have an upgraded user interface to Modtran here … the results are the same. I prefer the older version, the graphics are more informative, but that’s just me.
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D. J. Hawkins says:
April 12, 2014 at 12:57 pm
Perhaps the word “instantaneous” has a different meaning in your neck of the woods.
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Oh no! Thanks for the correction.
“But yes, of the three computer languages I learned during the 1960s (ALGOL, COBOL, and FORTRAN), only one survives”
COBOL and FORTAN are still in widespread use. Btw. Fortran was called FORTRAN up until and including the 1978 ANSI standard. After that it was “Fortran”, it was never “ForTRAN” as the article suggests.
Forgive my ignorance, I’m new to MODTRAN, but I thought I’d take a look up from the ground and observe the infra red coming down. I put zero in for the height above ground and also put zero in for the amount of CO2, CH4 and Ozone. I set the locality to Mid Latitude summer with no rain or cloud cover ,( just leaving H20 vapour, O2 and N2 presumably) and changed the display to wavelength. I observe a near blackbody curve at approx 10um corresponding to a temperature of about 290K, with a chunk taken out of it. So where’s it coming from as it isn’t the Sun, that has a different blackbody curve. I thought gases only emitted spectrally.
Looking up also makes it easier to see the amount of back radiation coming down due to changes in CO2. A doubling of CO2 gives a change of down radiation of approx 2.1 W/m2.
Willis, you used modtran to calculate the impact, from what I can understand Hansen did not necessarily use modtran. Has he in fact stated how he came by his number and how can one critique a result if the methodology usewd to compute it is not known? However, when faced with a result one is not sure about, a very good way to check it is to calculate the result by some completely different means and see if the results roughly agree. In this case, Heinz Hug has measured the absorptivity of the atmospheric column of CO2 at 280 ppm as around 2000 abs. If we take the saturation point of the line center as approximately 2 abs (an amount that would absorb 99% of incident 14.7 micron radiation) that means the atmospheric column at 280 ppm is about 1000 times the saturation point of the line center (the logarithmic relationship starts when the line center saturates because from that point on incremental absorption is due to line broadening and thats a logarithmic relationship). 1000 time saturation is 10 doublings (2^10=1024). Now the generally accepted contribution of CO2 to energy retention is around 27 watts/sqM to 32 watts/sqM. That means the sensitivity is between 27/10 and 32/10 or 2.7 to 3.2 watts/sqM which agrees very well with your modtran result. For Hansen to be right, the contribution of CO2 to warming would have to be around 45 watts/sqM which I have not seen suggested.
For anyone claiming that CO2 does indeed retain 45 watts/sqM the calculation is a simple one. The impact of CO2 is to block radiation from the surface (over the absorption band) and replace it with radiation from the top of the CO2 column which is about the tropopause – 288K for the surface versus 220K for the tropopause. Numerical integration of pascals equation for the two temperatures over the line width and making some allowance for the imapct of clouds yields a difference in emission to space between no CO2 and CO2 at 280 ppm of around 27 watts/sqM. My money is on your result.
One point of very considerable interest (although not unexpected) in the plot you showed is the spike in the middle of the CO2 absorption band and the spike in the middle of the O3 absorption band. This shows that CO2 is NOT well mixed in the stratosphere as many sources claim but instead is highly stratified pooling in the lower stratosphere where the temperature is almost the same as at the tropopause.
george e. smith says:
April 12, 2014 at 6:18 pm
It [ Beer-Lambert Law ] does NOT apply to the TRANSMISSION of energy through the sample, because most if not all materials RE-RADIATE the absorbed energy as some other wavelength radiation.
More problems with Beer-Lambert. Necessary conditions for its application include homogeneous, no scattering, same length of medium and monochromatic.
Homogeneous, no. The atmosphere has a pressure, temperature and density profile.
Scattering, yes. The sky is blue and clouds are white.
Path length same, no. Midday light is not the same as at sunset
Monochromatic, no. Sun’s light has a range of frequencies.
Beer-Lambert Law is incorrectly applied to the atmosphere. Radiative-convective models are wrong.
I used IR spectroscopy and beer-Lambert Law as an analytic tool in 1970’s. Extending it, wrongly, to the atmosphere is due to IR trained graduates looking for research money and politicians looking to demonize CO2.
Roy Clark says:
April 13, 2014 at 12:15 am
There is another way to look at this issue.
“Radiative forcing is based on the assumption of an ‘equlibrium atmosphere’ in which perturbation theory is used to ‘predict’ the effects of an increase in atmospheric CO2 concentration on surface temperature. It is a mathematical ritual that has no basis in physical reality. There is no equilibrium, and it goes downhill from there. …………………………”
And….
“Rather than argue over meaningless forcings, feedbacks and climate sensitivities, perform the real engineering calculations of the climate heat transfer. CO2 induced global warming then disappears into the noise of the surface fluctuations. There is no such thing as an average climate, average temperature or average flux…..”
Thanks Roy. This makes the most sense to me…
The 3.7 W/m2 from doubled CO2 that is commonly used by climate science and the IPCC come from Myhre 1998. This paper used Hitran.
(the climateaudit link to the paper seems to be the most stable of the 2 or 3 out there).
http://www.climateaudit.info/pdf/others/myhre.1998.pdf
This paper made an adjustment for the shortwave impacts in the stratosphere. This is also where the formula 5.35 ln(CO2ppm/CO2orig) came from. It is remarkably lacking in detail and explanation. Myhre hasn’t done much since this paper.
Sometimes, doubled CO2 forcing estimates also includes the impact from Methane, N20 and the CFCs that are expected to be there when CO2 reaches doubling which can bump the forcing number up to 4.2 W/m2 which is the number I always use.
But this forcing is not showing up.
The TOA energy imbalance is only 0.6 W/m2. The oceans, land and atmosphere are only accumulating 0.5035 W/m2. Where is the 5.35 ln(397/280) = 1.9 W/m2 CO2 forcing and the additional 0.8 W/m2 from all other GHGs showing up?
Its not there.
It’s not there because the tropics have a strong negative feedback.
http://climategrog.files.wordpress.com/2014/03/tropical-feedback.png?w=777
If it works radiative forcing from volcanoes it probably works CO2. The forcing is there, it just gets corrected by negative feedbacks.
Mainstream have spent the last 25 years doing everything possible to avoid the obvious: that a stable climate is dominated by negative feedbacks. They’be been desperately trying to make things work with positive water vapour feedbacks but this has included dropping the Lacis et al 1992 value of 30 W/m2 * optical density to 21 W/m2 * optical density in order to get the models closer to the climate record.
Rather then fix the model (be adding neg. f/b) they “corrected” in the inputs.
Yet another case of don’t fix the model, fix the data.
daveburton says; “The results from the old MODTRAN page showed water vapor amplification for clear sky and tropical atmosphere to be about +65%, but the new MODTRAN page calculates it to be only about +8%, i.e., almost, as Ferdinand said, exactly the same as with constant water vapor pressure.”
Very interesting. It appears someone has been tweaking MODTRAN. It will be interesting to see whether you get a credible reply.
I was wondering whether there wasn’t another web interface to MODTRAN an came across this:
http://www.realclimate.org/index.php/archives/2007/10/my-model-used-for-deception/
It looks like David Archer’s site that I cam across years ago, was calling the U.C. installation.
But if this is run by someone linked to RC, you can bet your arm they been “correcting” the source code.
BTW Moderate Resolution Atmospheric Transfer (MODTRAN) code, not some amalgam with Fortran.
http://climateaudit.org/2008/01/14/from-lacis-et-al-1981-to-archer-modtran/
MODO 4 contains original MODTRAN 4 executables , MODO is commercial software but trail 30d licences are available on request.
http://www.rese.ch/download/index.html
For anyone wanting to check out ‘old’ versions this may be a good option.
The currently “accepted” (and also now used by IPCC) formula comes from Myhre in 1998:
ΔF = 5.35·ln(C1/C0) [W·m-2]
Thus for doubling of CO2 concentration the forcing would be 3.71 W·m-2 .
The 4.52 forcing figure cited here comes from an older Hansen paper (1988). It is calculated from the old equation ΔF = 6.52·ln(C1/C0) which IPCC was using in erlier assessments.
The Myhre estimate is derived from line-by-line, narrow band and broad band molecular models.
Ref: Myhre et al.“New estimates of radiative forcing due to well mixed greenhouse gases.”, Geophysical Research Letters, Vol. 25, No.14, pages 2715-2718, July 15, 1998, http://folk.uio.no/gunnarmy/paper/myhre_grl98.pdf
Note also that Myhre evaluates the forcing due to changes in concentration of all Well Mixed Greenhouse Gases (CO2, CH4, N2O, CFCs) at 2.25 W·m-2 (CO2 concentration was 374 ppm when he made this assessment, it is now approaching 400 ppm, an additional forcing of 0.36 W·m-2).
The MODTRAN programm is based on line-by-line band models with a width of 1 cm-1. This may be too coarse and miss lines.
Finer absorption spectra with 0.01 cm-1 band resolution can be obtained here:
http://spectra.iao.ru/1280×796/en/home/
Note that absorbance is also temperature dependant.
If you want to play with standard atmospheres (tropical, polar, temperate, etc.) there are quite a lot of numbers to crunch.
Spectra examples of various air mixtures:
https://db.tt/QeNwYzem
https://db.tt/bB87DiXK
https://db.tt/dqEFkF7l
bones says:
April 12, 2014 at 4:49 pm
M Simon says:
April 12, 2014 at 3:49 pm
Willis,
You say “which calculates the result for each 1 cm-1 wide band of the wavenumber across the spectrum.”. I might believe 1um. Or 100nm. Or 10nm. (I know nothing of MODTRAN) But 1/1cm seems rather broad. At 1cm you are more into microwaves than light. Although really it is all light. But common nomenclature.
———————————————————–
A reciprocal centimeter bandwidth is just an increment of the spectrum over which the calculations were performed.
*******************************************************************************8
Well I’m an EE I get that. (actually 1/f – but I digress)
What I was pointing out that MODTRAN probably does not calculate the absorption over 1 cm intervals. It calculates them over nm intervals. So lets see 1/1cm = 30,000,000,000 Hz. 30E9 for short. At 500 nm
the frequency is 600E12 Hz. Add 30E9. Convert back to wavelength and you get 499.9750e-9. Roughly. So that I could believe. .025 nm intervals at 500 nm. It does seem excessive though for a MODerate program.
It would make more sense to me to state that it is calculated over some x nm interval or better over some frequency interval to say it is calculated over 1/1cm intervals is confusing. But I don’t operate in that domain. Maybe the nomenclature used is standard.
politicians looking to demonize CO2.
Tax it actually. But demonization is a step on the way to taxation.
I used the MODTRAN online tool Willis pointed us at the look at upwelling radiation at 0.1km in a US standard atmosphere. The result is essentially black body radiation at 288K.
But if I’m over the ocean, is upwelling IR really black body? Won’t it be influenced by the chemical composition of the ocean? I don’t know much about this space, but I’d have thought the H2O in the ocean would emit pretty much on the atmospheric H2O absorbtion spectrum, making the H2O GHG effect even greater over the oceans.
Commercial MODTRAN has some ‘liquid water surface options’…..anybody seen anything on that?
Willis
Here is a VERY good early paper on the subject.
The Influence of Carbon Dioxide Variations on the Atmospheric
Heat Balance:
By LEWIS D. KAPLAN, Massachusetts Institute of Technology
A special note here is that Gavin Schmidt, James Hansen, et al, specifically trace their lineage in climate science back to Plass. They ignore Kaplan because he, using the actual data gathered by the USAF for their “upper atmospheric research” (aka research into IR sensors for heat seeking missiles), shows that Plass’s numbers are much too high. The paper goes into the details on the subject.
This was back when scientists were driven by science, not ideology.
Thus for doubling of CO2 concentration the forcing would be 3.71 W·m-2 .
The 4.52 forcing figure cited here comes from an older Hansen paper (1988). It is calculated from the old equation ΔF = 6.52·ln(C1/C0) which IPCC was using in erlier assessments.
IF you go through earlier references in Hansen, he gets his numbers from Plass, who calculated the number at 3.8 w/m2 in the mid 1950’s
_____________________________________________________________
PLASS,G, . N., 1956 a: The influence of the 15 p carbondioxide
band on the atmospheric infra-red cooling
rate, Quart. J. Roy. Meteor. SOC8. 2, pp. 310-324.
PLASS,G, . N., 1956 b: The carbon dioxide theory of
climatic change, Tellus 8, pp. 140-154.
PLASS,G, . N., 1956 c: Etfect of carbon dioxide variations
on climate, American J. of Physics 24, pp. 376-387.
PLASS,G, . N., 1959:C arbon dioxide and climate, Scient$c
American 201, pp. 41-47.
___________________________________________________________
If you go to Gavin Schmidt’s work he acknowledges Plass, but ignores Kaplan, who in 1959 showed that Plass’s numbers were high by a factor of 2-3
The Influence of Carbon Dioxide Variations on the Atmospheric
Heat Balance:
By LEWIS D. KAPLAN, Massachusetts Institute of Technology
Net fluxes of radiation in the IS micron carbon dioxide band at the top and bottom of the
atmosphere have been calculated for several atmospheric models and with various cloud heights.
The variation of the fluxes with carbon dioxide amounts is determined, and its effect on temperature discussed. Plass’ estimate of a temperature drop of 3.8′ C due to a halving of the carbon dioxide concentration appears to be too high by a factor of two or three.
“””””…..Jim s says:
April 12, 2014 at 12:12 pm
Well, and I might be wrong, but the theory of CAGW does not rely on CO2 alone. The theory states that increasing CO2 leads to increasing H20 …..”””””
Well increasing H2O itself leads to decreasing surface Temperatures, so that would not be an enhancing effect even if it were true that more CO2 gives more water.
Willis, here is a reference to the original somewhat arbitrary definition of the bottom and top of the atmosphere by Kaplan, who uses Plass’s definitions. A lot of this stuff was originally decided in the 1950’s, but modern climate scientists simply assume it without delving into whether the assumptions used back then are still valid..
The 1,000 millibar level was taken as the bottom of the atmosphere and the IOO millibar level as the top of the atmosphere. The net upward flux was calculated at both of these levels as a function of thermal structure and cloud heights. The bases and tops of clouds were chosen in hundred millibar intervals; and the lapse-rate of temperature was considered constant with height. It was assumed that the ground temperature was the same as the adjacent air temperature.
This is from the paper by Kaplan referenced above…
“””””…..RERT says:
April 13, 2014 at 8:19 am
I used the MODTRAN online tool Willis pointed us at the look at upwelling radiation at 0.1km in a US standard atmosphere. The result is essentially black body radiation at 288K.
But if I’m over the ocean, is upwelling IR really black body? Won’t it be influenced by the chemical composition of the ocean? I don’t know much about this space, but I’d have thought the H2O in the ocean would emit pretty much on the atmospheric H2O absorbtion spectrum, making the H2O GHG effect even greater over the oceans……”””””
Rert, you are confusing apples with oranges.
The deep oceans act rather like a “Black Body” in that at least within the range of the solar spectrum; what goes in never comes out.
I can confirm, from fishing on the quiet Sea of Cortez, that the deep ocean shielded from the sky, looks black and NOT blue. (did the experiments myself).
Consequently one would expect the ocean surface to emit somewhat like a black body in a thermal spectrum dependentonly on the ocean Temperature.
That spectrum, is centered in the 10.1 micron region (288 K), and as luck would have it, the absorption of water at those frequencies, is almost total in just the top 100 microns of water.
So the expected emission from the ocean is indeed a 288 K or thereabouts thermal (BB like) spectrum, and since that is 70+ % of earth’s surface, it must be what the earth largely looks like from space (sans clouds ).
You won’t see much of any H2O characteristic spectral lines from a warm ocean surface.
Willis: Others have noted that radiative forcing is defined as the NET change in flux at the tropopause after the stratosphere has come into equilibrium with the changed CO2 or other forcing. Unlike the troposphere, where convection plays the major role in determining temperature, temperature in the stratosphere is controlled by radiation and the equilibrium temperature change at all altitudes can be determined by using the forcing to predict a modified temperature profile, using the modified temperature profile in a new radiative transfer calculation, and repeating this process until the results converge. I don’t know if MODTRAN has this capability.
Radiative forcing is the NET change in flux across the tropopause. You should set the “Altitude” to LOOK DOWN and to LOOK UP from the tropopause (a different altitude in the tropics, midlatitudes and the poles). With more CO2 in the stratosphere, its radiative cooling is enhanced and its temperature drops. Therefore, the DOWNWARD flux from stratosphere will drop from the lower temperature (if the calculation allows the temperature to change) and from the increased opacity from CO2. Both factors should REDUCE the calculated reduction in in the UPWARD flux.
Hansen’s value of 4.5 W/m2 for 2XCO2 was reduced to 3.7 W/m2 by more precise work, mainly by Gunnar Myhre et al. He appears to be most responsible for the IPCC “consensus” on this subject. A Google Scholar search of his name and “radiative forcing” will turn up many papers that are not behind paywalls. I remember looking at the paper below, but being frustrated that his complete methodology was spread over multiple papers.
http://go.owu.edu/~chjackso/Climate/papers/Myhre_1998_New%20eatimates%20of%20radiative%20forcing%20due%20to%20well%20mixed%20greenhouse%20gasses.pdf
Talking about MODtran / HItran / LOWtran / whatever , I’m under the impression that these calculations do accurate quantum mechanical computations of ALL of the myriad of molecular spectral lines that each gas component can generate / absorb; at least for any single GHG molecule, based on the known energy levels of these molecules.
So what the very coarse low resolution IR spectrometers claim for GHG absorption bands, are in fact these complex arrays of many fine lines.
I happen to have an actual high resolution chart for the atmospheric transmittance of a 10 km long path at sea level, in the “Infrared Handbook.” in chapter 5 fig 5.2 It is hundreds of lines, and yet covers only 0.025 micron bandwidth, from 10,900 to 11,200 cm^-1.
They say it was computed using line by line numerical integration. There’s too much info in the reference, but it is from the Air Force Research Lab from 1974. R.A.McClatchey, and J.E. Selby relating to laser attenuation, and it appears to be a multiple layer (atmosphere) integration. The math is too obstruse for me to describe here, or I would be here all day.
Some years back I described a hypothetical “Cocktail Party Physics ” situation; which at the time caused Dr, Roy Spencer to spill his coffee..
Suppose we had a WUWT cocktail party at some Las Vegas hotel Ballroom; maybe a thousand or so of us, having a good time networking..
Well there would of course be some stars present, like Anthony and Willis, Dr Roy, and Prof Lintzen, and Prof John Christy; well even Michael Mann, might show up.
Well everyone wants to hear from the stars, or at least try to bend their ears.
So there’s Dr. Roy, with a ring of six fans around him, each trying to get his attention. Beyond them a second ring of 12, just like a 19 strand cable. The third ring of 18 makes 37 folks almost none of whom, are actually able to talk to Roy.
Well Willis has the same problem, and also Leif Svalgaard; they are all being mobbed.
So Dr Roy thinks of something he meant to tell John Christy; but there is not a snowball’s chance in hell, of him, being able to see John in that crowd, or even know where he is in the ballroom.
Roy is totally isolated, and will have to tell Christy later.
So this is exactly what it is like for a single CO2 molecule in the atmosphere. The next fan mobbed star at the party, is actually isolated by about 13 layers of, by now half drunk WUWTers
As far as one CO2 molecule is concerned in the atmosphere, there is not another like it in the whole universe; it is alone and must field the questions (or photons) all by itself.
So nyet on the idea that these CO2 stars, are part of a giant conspiracy acting in consort; each is totally isolated, and obivious to anyone else of influence.
Now Mother Gaia of course knows where every single CO2 molecule is. She keeps track of all of them, and every time one makes a catch or tosses out a pitch, MG makes not of it, and updates the score accordingly.
Well we can read the scoreboard, and see what the total is, but we never see the play by play like MG does.
So the atmosphere does what it is supposed to do, but the idea that the GHG molecules are co-operating with each other is just plain silly.
So what if a certain layer thickness of air has enough CO2 molecules in it to grab all the photons in a certain 15 micron “band”, and then release them somewhat shaken up by the cocktail party jostling.
If we add more stars, well it just takes a thinner layer to grab all the available photons of the right kind, and then quickly release them to wander round the ballroom, until they run into the next star centered bunch.
So forget about this “saturated” business; all it means is that more catch and release events happen, but it doesn’t mean the fishing stops.
Also the notion that somehow the increase in CO2 somehow just “nudges out the edges of the absorption “band” and that results in the “logarithmic response to the CO2 increase.
Well surely that too is nonsense, given that the “band” is really a large number of narrow lines, and each CO2 molecules is quite unaware of the presence of any others. Any of those lines is going to behave pretty much the same, all the time.
Dear willis, FYI, I posted comments as tom watson and toms3d. So I wil repeat I find your posts and analysis informative and interesting.
As to.
Willis Eschenbach says:
April 12, 2014 at 2:48 pm
“Since you haven’t provided the slightest scrap of evidence for your claim that Modtran has significant errors, it seems that you are not intelligent enough to understand that on a scientific website, claims are meaningless without facts, logic, math, or observations to back them up.”
As you say I did not read the current modtran manual. I am in the middle of integrating a migration from fc13 to ubuntu 13.10 and firefox crashes are my lame excuse. But Fact even NIST cannot provide molar absorptivity values. Do you believe in an extinction coefficient distance?
Damn, as I came up with, well tried to come up with a visual analogy I saw why my objections to modtran were not consistent with what I saw in my mind. I have run modtran varying altitude and humidity. I’m not sure what is defined as relative humity. Using dewpoint temp would be specific. Can I assume 100% humity at a temp is using that as a dewpoint?
Let us assume modtran can tell us what is the Iout way up or wherever.
So what does modtran imply if your use relative humidity of 100% at different temps and vary C02. There is no change in Iout. What are the prevailing dewpoints as you get to the tropics. Where is most of the suns Iin hitting the earth.
I still did not read the modtran manual, but changing locality simply changes the ground T offset = 0 temp.
Consider, if the dew point is 45F vs 70F. H20 ppm varies from. 10K ppm to 25k ppm.
The tropic locality uses 299.70 which as a dewpoint gives 35K ppm of H20
http://toms.homeip.net/global_warming/SpreadSheets/Goff-Gratch-ppm-h20.sxc.gif
see spreadsheet. http://toms.homeip.net/global_warming/SpreadSheets/Goff-Gratch-ppm-h20.sxc.gif
H20 as vapor simply looking at global dewpoints is absorbing all the IR that is to be absorded.
I guess modtran can tell us something. It’s all how you ask it questions. It’s all how you interpret the meaning of the results.
Willis, I love your posts. They get me thinking. Thanks again. Now back to finguring out why firefox 28 keeps crashing my u13.10 arrrgggh….
[Errors happen, but Site policy requires you use only one login_ID. Mod]
[Errors happen, but Site policy requires you use only one login_ID. Mod]
I donot comment regularly in wordpress blogs. I go to leave a comment not logged in and fill in my name etc and then when I post I have to log in. The post says Tom Watson the name I entered. It seemed that when I posted already logged in the software used my login user name toms3d sayes. Not certain what was what I figured full disclosure was the best course of action.
tom watson aka toms3d
Berényi Péter asked, “What’s the definition of parameter Water Vapor Scale in MODTRAN?”
Hover your mouse over the various input names, and a brief description appears at the bottom of the input form. For Water Vapor Scale the description is, “Multiply the standard model tropospheric water vapor concentration by this fraction.”
Another thing that’s not obvious on that page is that if you enter a non-zero temperature offset then an additional input field appears, which allows you to choose between constant water vapor pressure and constant relative humidity (with the later effectively incorporating the “amplification” effect of water vapor).
Also, there’s a slightly improved version of that page here:
http://lorelei.uchicago.edu/modtran/
BTW, would you mind please sending me an email? Thanks.
If you haven’t figured it out since <a href="http://wattsupwiththat.com/2011/08/18/odtran-moddities/"Aug 13, 2011
then you simply aren’t trying to understand.
the answer is basically very simple.
you are trying to solve a jigsaw puzzle using a hammer.
http://data.giss.nasa.gov/cgi-bin/cdrar/effij.cgi?xx=efficacy&quantity=0&mean_gen=ANN&type=Fi&mod=E2c2&nobanner=0
Here is another mystery for you!
I had posted a comment earlier. I wanted to save the location of the comment so I saved the URL of the comment to a Word file, selected the text, and clicked on Insert>Hyperlink to make the URL active.
http://wattsupwiththat.com/2014/04/12/a-modtran-mystery/#comment-1612185
But when I click on the link in Word, it returns the error message:
“Unable to open http://wattsupwiththat.com/2014/04/12/a-modtran-mystery/%23comment-1612185. The internet site reports that the item you requested could not be found. (HTTP/1.0 404)”
Note that the “#” sign in the URL was changed to “%23”. The text of the URL in Word shows the “#”, and hovering the cursor over the link displays the URL link with the “#”. Copying the link directly back to the browser makes WUWT display “Apologies, but the page you requested could not be found.” Changing the “%23” in the browser URL bar back to “#” correctly displays the comment.
Why does Word change the “#” to “%23” in the URL (but displays the “#” as the hyperlink)?? This appears to be a recent problem.