A Modtran Mystery

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 and the increased H20 creates hot spots in the tropics and it’s these hot spots (via more H2O) that do the warming. CO2 by itself can’t. I’ll only add (the good news) that no hot spot has ever been detected and no increase in H2O has been observed.

Emission happens typically 1 ns after absorption.

Yes, this is very odd indeed. I look forward to an explanation from Nick Stokes!

I would not rule out the possibility that the issue that you uncovered is known, but ignored by climate modelers. It would be just one more “parameter’ that needs to be “adjusted” to give them the answer that they want. Very similar to the residence time of CO2 in the atmosphere. When no one was concerned about it and it was a purely academic exercise the residence time was around 10-12 years. Once it became a “parameter” it was “adjusted” up to 100 years to fit the IPCC models.

FYI ” . . . Table 1 of “Efficacy of Climate Forcings” , James Hansen et al . . .” loaded a moment ago.

The GISS zonal maps for instantaneous forcing for 2xCO2 and 1/2CO@ are the nearly precise inverse of each other. It’s not obvious to me why removing half of say 350 ppm should have the same effect, inverted, as adding another 350 ppm,

If it is linear, it should be the same thing but I think the doubling is usually taken from an assumed pre-industrial baseline of 280 ppmv.
I’ve also seen the usual figure for unamplified CO2 to be 3.7 W/m2/K.

The main reason for that is in the influence of stratosphere. Radiative forcing is defined as a change in the flux just above troposphere after stratospheric temperatures have reached the new radiative energy balance, i.e., after the stratosphere has cooled. UChicago MODTRAN does not allow for cooling stratosphere. Results calculated at 17 km looking down are closer to the correct ones, but fully correct values require a model that makes the stratospheric corrections.

Please continue with your Modtran mystery research. May i suggest that you check heat balance and heat transfer in Modtran. How the energy that is radiated towards space at a certain level reach that level from earth.
Clue: it can not be done by radiation

daveburton says:
April 12, 2014 at 12:53 pm
Something has changed in the online MODTRAN calculator.
Indeed, in the current online version refered by Willis, you still can choose between water vapour influence as pressure or relative humidity, but the results are exactly the same…
In another version at the same university, you can’t even choose the water vapour effect anymore:
http://climatemodels.uchicago.edu/modtran/
WUWT?

I was curious where global warming was suppose to warm.
Your results results don’t seem to include the idea that arctic was suppose to get more warming
than anywhere else in the world.
Generally don’t think CO2 does much warming and few watts per square meter sort of goes along with what I assume.
As to your question, maybe Hansen simply applied it global vs doing regionally. And I would guess
doing this should distort the results. But I also think by doing it regionally one also distorts the results. So I find it interesting and interest topic to discuss. Likewise, I would interested in comparison between night and day, though the winter and summer sort does this.
It seems to be global warming is entirely about night time and winter increase in temperature, just any greenhouse effect on the Moon would be entirely about night time and polar warming. Or global warming is not going to increase daytime surface temperature on the Moon of around 120 C, but it could dramatically increase nighttime temperature on the Moon.
And on Earth, if one talking about time of when Earth had average temperature of 25 C, I would not expect much increased temperatures in tropics [maybe less cooling at night in tropics] but mostly expect the Temperate Zones to have a significant increase in average temperature. Or it would be tropical in sense one doesn’t get freezing temperatures at night- and therefore tropical plants could grow in these regions- you can grow orange trees in Oregon or even Canada.

FORTRAN? Now that brings back some memories. I didn’t know anyone used FORTRAN anymore. I wonder if they store the source code on punch cards? Just kidding, I loved FORTRAN.

@ george e. smith says:
April 12, 2014 at 2:02 pm
…
And if they are assuming a log base 2 behavior, that means they believe Beer’s Law applies, and it doesn’t because Beer’s law presumes the absorbed photons stay dead, and are never re-emitted at any wavelength.
…
That isn’t an assumption of Beer’s law. If that were true, after a while the sample would transmit all light impinging upon it because all the molecules would have already absorbed photon. That isn’t how it happens – it is a dynamic equilibrium of absorption-emission.

What Roy Spencer says – 285 and 570 rather than 375 and 750. Probably a log relationship (or two) rather than linear.

OK – When all else fails then either Hansen or Modtran is wrong. I know who I’m betting on.

Boy, does this bring back memories. I wrote a program at GSFC during 1972-1982 called the Synthetic Spectrum Program (SSP) (re: Rudy Hanel, Virgil Kunde, et al.) with parameters to describe the various atmospheres we wanted the simulate in the IR for remote sensing analyses: Earth, Mars, Jupiter and Saturn. It was written in FORTRAN. I remember a copy was sent to NCAR in the early 80’s. I verified that the program (substantively unchanged) was still in use in the mid-90’s. I wonder how much of that program is the basis for later models? The SSP did a very good job in a clear atmosphere. Clouds & aerosols were (and I think still are) a confounding problem that we were not able to solve then.

Wikipedia says:

Forcing due to atmospheric gas
For a greenhouse gas, such as carbon dioxide, radiative transfer codes that examine each spectral line for atmospheric conditions can be used to calculate the change ΔF as a function of changing concentration. These calculations can often be simplified into an algebraic formulation that is specific to that gas.
For instance, the simplified first-order approximation expression for carbon dioxide is:
ΔF = 5.35 × ln C/C₀ W/m²
where C is the CO₂ concentration in parts per million by volume and C₀ is the reference concentration.

If C/C₀ = 2, that is, for a doubling of atmospheric CO₂ concentration this formula gives 3.7 W/m². However, the term “radiative forcing” in this case is probably not equivalent to the “instantaneous radiative forcing” used by MODTRAN. The wiki value may be related to the IPCC usage.

The radiative forcing of the surface-troposphere system due to the perturbation in or the introduction of an agent (say, a change in greenhouse gas concentrations) is the change in net (down minus up) irradiance (solar plus long-wave; in W/m²) at the tropopause AFTER allowing for stratospheric temperatures to readjust to radiative equilibrium, but with surface and tropospheric temperatures and state held fixed at the unperturbed values.

Sure it is a rather contorted definition, because
1. the “tropopause” is not a well defined surface (see tropopause folds)
2. allowing one side to adjust while holding the other side fixed excludes empirical testing.
“Instantaneous radiative forcing“, although it can’t be tested either, is a bit better, because

Radiative forcing is called instantaneous if no change in stratospheric temperature is accounted for.

This latter usage at least treats the entire atmosphere uniformly. Which is preferable, since heat capacity of the stratosphere is negligible, so the surface along which “forcing” is defined can be moved upward at leisure. Forcing at ToA (Top of Atmosphere) is the same as at the ill defined tropopause.
Now, the stratosphere is supposed to cool down with increasing GHG concentration. If this cooling is taken into account while the troposphere below is “held fixed”, it should increase radiative loss through the tropopause, because there is a larger temperature difference. Therefore the 3.7 W/m² given by the IPCC is an upper bound to instantaneous radiative forcing, which is consistent with your thought experiment using MODTRAN, but excludes higher values.
The NASA GISS ModelE Climate Simulations page you were referring to uses a somewhat more consistent termonilogy.

– “Fi”, the instantaneous forcing, is the radiative flux change at the tropopause after the forcing agent is introduced.
– “Fa”, the adjusted forcing, is the flux change at the top of the atmosphere (and throughout the stratosphere) after the stratosphere is allowed to adjust radiatively to the presence of the forcing agent.

That is, they call “adjusted forcing” what is referred to as “forcing” by the IPCC. Now, their values are based on the output of Model E
Fi = 4.52 W/m²
Fa = 4.12 W/m²
Note the Fa > Fi relation does not hold for Model E, which is truly amazing. But hey, all models are wrong, but some are useful. And in this case the higher the values are the more fit for purpose they’ll be, provided the “purpose” is to generate scare.
Otherwise all such calculation, including MODTRAN is based on assumptions about the “average” atmospheric temperature/moisture profile in different regions and/or under different meteorological conditions, which may or may not be adequate.
I reckon even the IPCC adjusted forcing estimate of 3.7 W/m² is too large (derived for the US standard atmosphere or some such artificial constuct). Based on your fiddling with MODTRAN it should be below 3 W/m² (but probably above 2.4 W/m²).
Relation between reality and theory is always difficult. For instance we understand clearly why the stratosphere should cool down with increasing GHG concentrations. And indeed, according to RSS, during the past 35 years temperature of the lower stratosphere has decreased at an average rate of -0.28 K/decade. The only trouble is that almost all the decline happened close to the beginning of observations, during the last 2 decades this rate is only -0.03 K/decade, almost an order of magnitude smaller.

I’m not sure if this has any relevance, but I notice Hansen defined fi to be the forcing at the tropopause, rather than TOA. MODTRAN in the screenshot appears to be set at 70 km altitude. Is it possibly being affected by absorption/overlap in the stratosphere?

From that known source of climate alarmism, Wikipedia:
In the earlier 1979 NAS report[12] (p. 7), the radiative forcing due to doubled CO2 is estimated to be 4 W/m2, as calculated (for example) in Ramanathan et al. (1979).[13] In 2001 the IPCC adopted the revised value of 3.7 W/m2, the difference attributed to a “stratospheric temperature adjustment”.[14]
So Hansen disagrees with the IPCC? Who should we believe now? IPCC? Hansen? Modtran?
The debate is so messed up we don’t even know which version of wrong to debunk!

Coldlynx says:
April 12, 2014 at 1:53 pm
—————————————
The problem is that instantaneous radiative forcing actually gives no true answer to the change in atmospheric temperature profiles due to changing radiative gas concentration.
What do radiative gases do? Warm low down cool high up.
This increases buoyancy imbalance and increases the speed of vertical tropospheric circulation. This non-radiative transport combined with evaporation is the primary energy transport mechanism away from the planet’s surface.
Increased radiative gases speed up the primary energy transport mechanism away from the planet’s surface.
It should also be noted that the role of radiative gases in radiative subsidence of air masses from altitude is critical in tropospheric convective circulation. No radiative gases, and this circulation will stall. The lapse rate is a product of strong vertical circulation across a pressure gradient. Without this circulation, the lapse rate would trend isothermal via gas conduction.
Assuming constant lapse rate or speed of vertical circulation for changing radiative gas concentration is a dead end. Hold these constant for increasing radiative gases and the flawed models of the climastrologists will always show low altitude warming.
Sir George Simpson warned against this type of radiation only garbage in 1938 –
“..but he would like to mention a few points which Mr. Callendar might wish to reconsider. In the first place he thought it was not sufficiently realised by non-meteorologists who came for the first time to help the Society in its study, that it was impossible to solve the problem of the temperature distribution in the atmosphere by working out the radiation. The atmosphere was not in a state of radiative equilibrium, and it also received heat by transfer from one part to another. In the second place, one had to remember that the temperature distribution in the atmosphere was determined almost entirely by the movement of the air up and down. This forced the atmosphere into a temperature distribution which was quite out of balance with the radiation. One could not, therefore, calculate the effect of changing any one factor in the atmosphere..”
Apparently the Church of Radiative Climatology didn’t get the memo 🙁

“”””””……jim2 says:
April 12, 2014 at 3:06 pm
@ george e. smith says:
April 12, 2014 at 2:02 pm
…
And if they are assuming a log base 2 behavior, that means they believe Beer’s Law applies, and it doesn’t because Beer’s law presumes the absorbed photons stay dead, and are never re-emitted at any wavelength.
…
That isn’t an assumption of Beer’s law. If that were true, after a while the sample would transmit all light impinging upon it because all the molecules would have already absorbed photon. That isn’t how it happens – it is a dynamic equilibrium of absorption-emission…….””””””
Beers Law, is a law from chemistry about the absorption of some “specific wavelength” by some molecular species in a dilute solution of that species.
It asserts that a path through such a solution absorbs a fixed percentage of the incident radiation for each length increment of the path length, or alternatively as a function of the concentration of the absorbing species. So if a one cm path absorbs 10% of the INCIDENT RADIATION at that specific wavelength, the next cm of path will absorb 10% of the remaining radiation of that incident wavelength., or if you like doubling the species concentration in a fixed path length , will absorb 10% of the incident, plus 10% of 90% of the incident radiation.
It applies ONLY to the ABSORPTION of the incident radiation.
It 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.
I have color glass filters which will extinguish a specific wavelength by four orders of magnitude; yet they transmit over around 50% of the radiant energy but at a lower frequency radiation.
The LOGARITHMIC RESPONSE of Beer’s Law, is entirely dependent on the absorbed radiation NEVER being re-emitted;
A claim of logarithmic absorption of radiation with concentration of an absorbing species, IS an assertion that Beer’s law applies.
It virtually NEVER applies to energy transmission, because the radiant energy refuses to stay dead.
If radiant energy is absorbed,, and not re-radiated as some fluorescence, or in the case of gases, the molecule returning to the ground state, then the Temperature must increase, and the energy either conducted away as heat, or else the material will radiate a thermal radiation spectrum based on the higher Temperature.
GHG absorption in the atmosphere does NOT obey Beer’s law, so it isn’t logarithmic, with concentration or thickness.
Whether or not authors claim Beer’s law applies; the logarithmic (or exponential absorption):
…..t = t0. exp (-alpha .s) is totally a consequence of Beer’s law assumption. So what if an undetected thermal radiation appears mysteriously as a result. Ocean warming is what leads to increased ocean energy emission in the LWIR, long after the chap who measured alpha has gone home to sleep.

Willis,
I was under the assumption that cooling the stratosphere ( which yields ‘adjusted’ response, not instantaneous ) tended to reduce forcing. I have been running some runs using the CRM ( column radiation model ) which used to underlie the CCM and found that the ‘adjusted’ forcing is greater than the ‘instantaneous’ consistent with what you have found. I’m not sure you can calculate the ‘adjusted’ by using this tool because it doesn’t allow you to specify a given profile for one run, then the same profile with a stratospheric cooling for a 2x CO2 scenario.

Willis
Use HITRAN line-by-line calculations. That’s how 3.7 W/m^2 was calculated. It’s more accurate than band models.

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. ”
Yes that’s right
– it also relies on copious amounts of deplorable bullshit and hokum models

Willis Eschenbach says:
April 12, 2014 at 6:37 pm
“Yeah, those dumb scientist chumps …”
————————————————-
Willis, that paper was written by empiricists using the variances demonstrated by one flight to call for much more of the same type of empirical experiment –
“A major problem with estimates of the short-wave and long-wave DRE of dust aerosol using satellite data and radiative transfer modelling is the lack of concurrent detailed information of the aerosol optical properties, atmospheric vertical structure and surface reflection properties. This can only be overcome by multi-disciplinary experiments”
The argument of the authors of that paper are congruent mine. (only my experiment design is better 😉 )

Silly Willis. You just forgot to check the box for the “applyn 10.76 mw-ovens for 30 minutes” option under the Trenberth tab .

It would appear the Hansen et al worked backwards from their temperature estimate of 3C.
http://www.giss.nasa.gov/research/briefs/hansen_05/

Willis,.
What temperature profile did you use?
Over the “tropics” (actually over the half of the planet centred on the latitude at which the sun is overhead), the temperature profile is not “American Standard” (tropopause 11-20km) but a profile where the Tropopause is a single point of inflection at an altitude of between 14 and 18km.
The strong emissions from the centre of the CO2 absorption band, roughly 630-710 cm^-1, are from an altitude of 15km at least, if they are to get to Space, that is they are mostly from the Stratosphere, not the Troposphere, in the tropics.
The implication is that emissions to Space from this band will INCREASE in the “Tropics” when CO2 is doubled, whereas over the Temperate zones there will be little change in emissions because of the extensive tropopause.
So the “radiative forcing” increase obver the tropics should reduce due to the increased stratospheric emissions.

The answer to you question is not a secret: positive feedback from water vapor.
That’s why Svensmark’s theory is so important to confirm or falsify.
If Svensmark’s theory is correct, then under certain circumstances, water vapor in the atmosphere causes cooling by negative feedback.

“””””…..dbstealey says:
April 12, 2014 at 7:27 pm
Another very interesting article from Willis. This is habit forming.
Also, george e smith is smarter than I am. He says:
I think the whole idea is rubbish (of CO2 induced warming)……”””””
I hasten to point out; nobody should think that I believe CO2 and other GHG don’t do anything in the atmosphere. That is NOT my point. The physics of molecular vibrational and rotational absorption spectra, which are typically manifested in the LWIR (and longer) region is well established, and that is NOT a hill “skeptics” should choose to die on.
But there are a lot of things, which do stuff in the atmosphere physically, that are well researched.
But do you guys, and gals ever read and understand some of the stuff Willis puts up here.
Did you not read his account of the MEASURED drop in surface solar brightness, in Hawaii, due to attenuation by major volcanoes, that persisted for some months. This is short wave solar energy that did not reach the ground.
And Willis showed that the Temperature signal from that MEASURED drop in surface solar irradiance, DID NOT even show up in the MEASURED Temperature record (even locally).
Roy Spencer nailed it; there’s a very powerful negative feedback loop operating via the clouds that simply wipes out all of these gnat level pestilences like CO2 and aerosols, and TSI variations, and a whole host of other things.
So long as Earth has its oceans, we couldn’t change the Temperature of this planet, if we wanted to.
And if we could, what would YOU set the thermostat to ?? And WHY ??

Berényi Péter says: “And indeed, according to RSS, during the past 35 years temperature of the lower stratosphere has decreased at an average rate of -0.28 K/decade. The only trouble is that almost all the decline happened close to the beginning of observations, during the last 2 decades this rate is only -0.03 K/decade, almost an order of magnitude smaller.”
Actually the change in stratospheric temps has everything to do with volcanoes and nothing to do with CO2: Note how the ever increasing CO2 since 1998 has no visible impact:
http://climategrog.wordpress.com/?attachment_id=902
Drawing straight line “trends” through anything in climate is nothing but deceiving. The practice should be banned and those who insist should be put before some kind of Nuremberg tribunal for crimes against humanity 😉

What’s the definition of parameter Water Vapor Scale in MODTRAN?

Pekka gave the first correct answer:
Pekka Pirilä says: April 12, 2014 at 1:20 pm
“The main reason for that is in the influence of stratosphere. … Results calculated at 17 km looking down are closer to the correct ones, but fully correct values require a model that makes the stratospheric corrections.”
Later, Nick Stokes gave the same answer, but actually provided numerical results, which was more useful.
Nick Stokes says: April 12, 2014 at 6:30 pm
“So I calculated Modtran at 17km, tropics.
375 ppmv CO2 – 289.0 W/m2 upwelling
750 ppmv 284.5 W/m2.
Difference 4.5 W/m2.”
Willis then noted we have to calculate the net flux at the tropopause, up – down flux, which increases the forcing to CO2 doubling in the tropics to 5.6 W/m2.
The IPCC says the global CO2 forcing is 3.7 W/m2 per doubling at the tropopause. I used Modtran to calculate the total earth CO2 forcing and got 4.62 W/m2, significantly higher than the IPCC value. Modtran calculates clear sky values in three regions; tropics, mid-latitudes and polar. I assumed the year average is the average of the summer and winter forcings for mid-latitudes and polar region.
The tropopause height and the net radiative flux for the three regions are:
Region Tropopause Net Flux
Tropics 17 km 5.60 W/m2
Mid-Lat 14 km 4.93 W/m2
SubArctic 10 km 4.27 W/m2
Assuming for the northern hemisphere, Tropics is 0 – 30 N, Mid-Lat is 30 – 60 N, SubArctic is 60 – 90 N, the clear sky Earth is 5.14 W/m2, weighted by the surface area of each region. Assuming a 65% cloud fraction, and Willis’ calculated cloud forcings for the tropics, the ratio of all-sky to clear sky forcing flux is about 90%. This gives the all-sky Earth forcing of double CO2 at 4.62 W/m2. These calculations are shown here:
http://www.friendsofscience.org/assets/files/Modtran.xls
So the real mystery is why Modtran gives such high CO2 forcing numbers. I suspect the answer is that the water vapor concentrations assumed in Modtran are too low. In my calculations I am not using the 1976 US Standard Atmosphere, which is known to have too low water vapor. But I suspect that the three regions also use too low water vapor, which would make the calculated CO2 forcings too high.

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.

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.

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.

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.

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/

Well, not my model exactly. I developed and host a web interface to the modtran model of atmospheric infrared radiation, an early example of a line-by-line code which I downloaded and use to teach and as part of a textbook. Now David C. Archibald from Summa Development Limited, Perth, WA, Australia claims that my “University of Chicago modtran facility” proves that global warming won’t happen.

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.

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: 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

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.

I like modtran. At one time I used it to initially validate the operation of my HITRAN 1-d model. Where there were descrepancies, I combed my code looking for problems and ultimately found them. I wouldn’t say there was perfect agreement but I thought it did a good job. Although I did play around with the model for AGW purposes, its purpose was for something different.
It became obvious that this sort of effort provides very little information because the co2 doubling is around 3.7w/m^2 in clear skies and the Earth typically has less than 40% clear sky. finding that hansen exagerates (or worse) is hardly a new discovery.
This is a nice article and worth learning for those trying to come up to speed on the subject. Modtran is a nice program (or was) and provides (or provided) reasonable information and is useful for gaining an understanding. It’s not really of much use for ascertaining proof or falsification of CAGW hype.

george e. smith says:
April 13, 2014 at 10:47 am
————————————
George,
with regard to the oceans acting as a “blackbody”, nothing could be further from the truth, they are in effect a ”selective coating” covering 71% of the lithosphere.
This is one of the greatest errors in the very foundation, not just of AGW, but the whole radiative GHE hypothesis. A fist-biting error. The greatest error in the history of human scientific endeavour.
Climastrologists have calculated a figure of -18C for the oceans in absence of an atmosphere. From this they conclude that the atmosphere is acting to raise ocean temperatures by 33C. How did they make this horrific mistake? The treated our deep transparent oceans as a blackbody and used only an emissivity value to calculate that a constant 240 w/m2 would give a standard S-B result of 255K. But you cannot use standard S-B calcs on transparent materials…
Empirical experiment shows that in the absence of atmospheric cooling and DWLWIR, the sun can drive our oceans to 80C or beyond. That’s a 98C error for 71% of the planet’s surface at the very foundation of the AGW inanity.
The simple dis-proof to all of AGW is this –
The sun heats our oceans.
The atmosphere cools our oceans.
Radiative gases cool our atmosphere.
97% of climate “scientists” are assclowns.
Want to make an AGW believer thrash and flex? Just ask them the simple question –
“Given an atmospheric pressure of 1 bar, is the net effect of our radiative atmosphere over the oceans warming or cooling?”
It really is that simple. A non-radiative atmosphere cannot effectively cool itself, therefore it cannot cool the oceans.

Everything that is at a Temperature higher than zero K emits a thermal continuum spectrum dependent on that Temperature.
At 300 k, that spectrum would peak at 10 microns wavelength. So at Temperature of 1 K, the radiation spectrum would peak at about 3,000 microns, or three mm in the microwave region.
So earth’s atmosphere is certainly emitting a thermal continuum spectrum peaked at somewhere in the 10-15 micron range.
But given the low molecular density, and hence collision rates, and the low collision energies at zero or lower Celsius Temperatures, the thermal radiant emittance is very low. For the main atmosphere gases, being diatomic, the radiative polar moments (antennas) are a transient consequence of distorting collisions.
Water molecules on the other hand, have a significant dipole moment due to the 104 degree bend, so it can emit quite well thermally.
So earth’s atmosphere is anything but non-radiative; just low density and emissivity.

Anyone here understand all this?

cba says: “It became obvious that this sort of effort provides very little information because the co2 doubling is around 3.7w/m^2 in clear skies and the Earth typically has less than 40% clear sky.”
Nope, the 3.7 W/m2 is for all-sky total Earth, net flux at tropopause with stratosphere adjustment, adjusted for solar absorption by CO2. It is not clear skies. See
http://folk.uio.no/gunnarmy/paper/myhre_grl98.pdf

Willis this is not just a scientific site you know. Arguments are proffered to counter stupid AGW
statements and politics. And the latest updates on various subjects, not just those that are scientifically based graphs, that I find very boring actually. Cut to the chase what is the conclusions of these observations. I am not at university any more but I can comment without giving references.

daveburton says:
April 14, 2014 at 12:29 am
———————————
The dye analogy doesn’t really work for radiative gases. This is because they act to both warm and cool our atmosphere. That is to say the warming effect decreases with increasing concentration, but the cooling effect increases.
The primary cooling mechanism for our atmosphere is LWIR to space from radiative gases in our atmosphere. In fact the amount of LWIR emitted to space by radiative gases is more than twice the net flux of radiation absorbed by the atmosphere from surface LWIR and direct solar radiation combined.
This is why MODTRAN is worthless for determining atmospheric temperature response to increasing levels of CO2 or any radiative gas for that matter. The only purpose for MODTRAN was determining atmospheric IR opacity for design of air to air missiles.
Radiative subsidence of air masses plays a critical role in governing the speed of tropospheric convective circulation, the primary energy transport away from the surface. Change the concentration of radiative gases and you change the speed of the primary energy transport in the atmosphere.
That is one of the old climastrology tricks. As radiative gases cool at high altitude and warm at low altitude, if you ignore buoyancy changes from increased radiative gases and hold the speed of tropospheric convective circulation constant, then models show low altitude warming.
Radiative gases both warm and cool our atmosphere. The cooling effect is more than double the warming effect. Adding radiative gases to the atmosphere will not reduce the atmosphere’s radiative cooling ability.

Berényi Péter says:
April 12, 2014 at 4:09 pm
Wikipedia says:
…For instance, the simplified first-order approximation expression for carbon dioxide is:
ΔF = 5.35 × ln C/C₀ W/m²
Plug in 2 and you get 3.7, as opposed to mod tran’s max of 3.2 over by 3.7/3.2 = 15.625
Plug in 100 and you get 24.638 as opposed to mod tran’s 25.497, under by
24.638/25.497 = 3.39%
Obviously, that logarithmic effect of CO2 is not exact, and the formula given by wikipedia is an approximation, intended to give fairly close values over a wide range of
changes in CO2.

I got very similiatr results using tools from the http://www.spectralcalc.com website, from Gats, Inc. Some are available at no charge. A full set requires an available subscription ($45 for a month, $95 for 3). It takes a lot longer to run than MODTRAN, but should be more accurate. One has to breakdown into runs a number of wavelength bands and each one can take up to a few minutes.
See my paper http://climateclash.com/does-the-tropopause-limit-carbon-dioxide-heat-trapping/
Summary of results below
“1. Summary of results
We found the reduction of heat radiated to space caused by two times CO2 from the following sources (in Wm-2): the surface with clear skies at 3.38, low clouds at 2.71, medium clouds at 1.03 and high clouds at -0.30. The combined weighted value is 2.53 Wm-2.”
“The value of 2.53 Wm-2 is considerably less than the presently accepted value of 3.71 Wm-2. This latter higher value is consistent with the widely cited paper by Myhre et al (1998) that provides an empirical equation to fit their estimates of CO2 forcing as 5.35 ln(C / C0). It is interesting that the ratio of all-sky/clear-sky forcing that we get of 2.53 / 3.38 or 0.749 compares closely to the Myhre et al value of 0.734, so this cannot explain the differences.”
After doing my paper, I read that more CO2 causes stratospheric cooling which some how causes the forcing to increase which requires a correction. I estimate this at about 15%. so I end up with 2.9 W/m2, still musc less 3.7. I think the 3.7 W/m2 accepted number is too large.
Some people claim the equilvalent thing of the corrction is to run the obsevation point at the top of the tropsphere instead of at 70 to 100 km at the TOA. However this misses out on the CO2 emissions around 15 microns where the absorptions are so strong that the final emissions level extend above the troposphere where the temperatures can actually rise with altitude, thus provide, more not less, heat to space with mode CO2. Figure 3 in my paper shows this and Figure 9 shows for clears skies measuring outgoing radiation reduction for 2x CO2 at 15 km around the top of the troposphere is about 50% higher than seen at 70 km. This is too much of a correction it seems. (BTW, how does a person paste a bimap here).
I would like to compare with MODTRAN. What is the cost?
Conclusions (from my paper)
“The results here using modern tools indicate substantially less (about 32%) radiation forcing heat unbalance caused by increased CO2 content then the presently accepted values such as in cited in Myhre et al. This brings into question estimates often cited as being the “settled” values from many years ago and whether they should be redone by others with new tools and techniques. Of particular significance is the fact that the estimates from the radiance tools used here match closely with satellite data for both clear and cloudy sky conditions. We were disappointed in the excellent paper by Kiehl and Trenberth (1997), that we used for part of our work, that the authors, after estimating outward radiation that matched satellite data quite well for existing CO2 content, did not repeat it for double CO2 as we did here. They did attempt to assign the relative importance of existing greenhouse gases, but this is of little value in answering the central question of climate sensitivity.”
Additional break down of results are below.
A2. CO2 forcing at the “Top of the Atmosphere” using the Radiance Tool
For each case of clear and cloudy skies, and for each bandwidth where CO2 is active, the outgoing radiation at 100 km from 1x and 2x CO2 were determined, and from that the increase. Each run took about 2 to 3 minutes. The results are shown below in the four tables. Note the significant reduction for the cases from the cloud tops. And at 10 km, the heat loss increases slightly with 2x CO2 because the altitude’s increase with temperature at the higher attitudes.
Table A1 – From the surface at 288 K with clear skies above; weighting = 42%
—————-Wavelength – Microns —————–
Condition 12 – 13.5 13.5 – 15 15 – 16.5 16.5 – 18 18 – 19 Total – Wm-2
CO2 at 330 ppm 30.20 13.28 11.31 15.83 9.92 80.55
CO2 at 660 ppm 29.15 12.34 10.82 15.08 9.88 77.28
Decrease 1.05 0.94 0.49 0.75 0.04 3.27
Note: Add 0.11 decrease from the 4 to 5 micron range
Table A2 – From cloud tops at 2 km at 275 K with clear skies above; weighting = 40%
Wavelength – Microns 
Condition 12 – 13.5 13.5 – 15 15 – 16.5 16.5 – 18 18 – 19 Total – Wm-2
CO2 at 330 ppm 26.18 13.10 11.25 15.39 9.64 75.56
CO2 at 660 ppm 25.49 12.29 10.80 14.74 9.60 72.91
Decrease 0.69 0.81 0.45 0.65 0.04 2.65
Note: Add 0.06 decrease from the 4 to 5 micron range
Table A3 – From cloud tops at 6 km at 249 K with clear skies above; weighting = 6% Wavelength – Microns
Condition 12 – 13.5 13.5 – 15 15 – 16.5 16.5 – 18 18 – 19 Total – Wm-2
CO2 at 330 ppm 17.70 12.13 10.79 12.62 7.79 61.03
CO2 at 660 ppm 17.49 11.80 10.58 12.35 7.78 60.00
Decrease 0.21 0.33 0.21 0.27 0.01 1.03
Table A4 – From cloud tops at 10 km at 223 K with clear skies above; weighting = 12%
Wavelength – Microns 
Condition 12 – 13.5 13.5 – 15 15 – 16.5 16.5 – 18 18 – 19 Total – Wm-2
CO2 at 330 ppm 10.58 10.40 9.69 8.89 5.44 45.00
CO2 at 660 ppm 10.57 10.57 9.85 8.87 5.44 45.30
Decrease 0.01 -0.17 -0.16 0.02 0.00 -0.30
Using the weighting described above, we get for the combined forcing for 2x CO2:
(A1) F = 0.42 x (3.27 + 0.11) + 0.40 x (2.65 + 0.06) + 0.06 x 1.03 + 0.12 x (-0.30) = 2.53 Wm-2
A3. Comparing the radiance estimates of total outgoing radiation with satellite data
The preceding work centered on the 12 to 18 micron range because this is the major band where CO2 plays a role. However we also used the radiance tool over the full range that virtually covers the complete longwave spectrum associated with the global average temperature. The results are shown in Table A5. The total leaving the top of the atmosphere under clear skies is estimated at 265.9 Wm-2, close to the satellite data of 265 Wm-2 as reported by Kiehl and Trenberth (1997).
Table A5 – Radiation leaving the surface and the atmosphere by wavelength (clear skies)
Wavelength – Microns 
4 – 8 8 – 12 12 – 18 18 – 100 Total – Wm-2
GHGs active All O2, O3 CO2, H2O H2O ––
From Surface (Wm-2) 46.83 99.10 110.60 132.49 389.1
Leaving Atmosphere (Wm-2) 15.61 88.85 70.63 90.81 265.9
Percent Leaving Atmosphere 33.3 89.7 63.9 68.5 68.3
When this was repeated for the three cloudy cases, the totals dropped from 265.9 to 240.2, 188.2 and 135.2 Wm-2. The combined total, using the weighting above, drops to 235.4 Wm-2, compared to 235 from Kiehl and Trenberth.
The agreement of the radiance tool with satellite data regarding outgoing radiation provides confidence in using it to estimate how it will change with increased CO2 concentrations.

Hmmm, guys I thought that space was freezing cold and a vacuum. Maybe my physics teacher was wrong.

Testing pasting Table in Courier Font
Table A1 – From the surface at 288 K with clear skies above; weighting = 42%
Wavelength – Microns
Condition 12 – 13.5 13.5 – 15 15 – 16.5 16.5 – 18 18 – 19 Total – Wm-2
CO2 at 330 ppm 30.20 13.28 11.31 15.83 9.92 80.55
CO2 at 660 ppm 29.15 12.34 10.82 15.08 9.88 77.28
Decrease 1.05 0.94 0.49 0.75 0.04 3.27
Note: Add 0.11 decrease from the 4 to 5 micron range
[The mods recommend using the [pre] and [/pre] (with angled html-brackets instead of square brackets) to generate tables from text using a fixed-width non-proportional font. Mod]