Robinson and Catling model closely matches data for Titan’s atmosphere

Posted: June 29, 2014 by tallbloke in solar system dynamics

.

.

Here’s an interesting post originally published at Verity Jones’ excellent blog ‘Digging in the Clay’, from Peter Morecambe, AKA Galloping Camel. He has found a model which reproduces atmospheric profiles well, rather than just surface temperature and an approximate profile to the 100mb level.

Digging in the Clay

Posted by Peter Morcombe, April 2014

“Climate Science” is a strange discipline that makes all kinds of claims that lack any valid mathematical basis. For example, the Arrhenius hypothesis:

“The selective absorption of the atmosphere is……………..not exerted by the chief mass of the air, but in a high degree by aqueous vapor and carbonic acid, which are present in the air in small quantities.”

I write about “Climate Science” because it is used to justify a political agenda that aims to “mitigate” CO2 regardless of negative impacts on billions of people. Even though most “Climate Scientists” get their pay checks from governments they are reluctant to engage with members of the public who express doubt about the need to reduce the atmospheric concentration of carbon dioxide.

Before making a post I reach out to experts in the field. For example, Tom Peterson (GHCN), Albert Klein Tank (KNMI), Richard Alley (Penn…

View original post 695 more words

Comments
  1. Stephen Richards says:

    Before making a post I reach out to experts in the field. For example, Tom Peterson (GHCN), Albert Klein Tank (KNMI), Richard Alley (Penn

    Blimey, that’s a cabal of geniuses 🙂

  2. tchannon says:

    I wonder if this uses simple NEF (net exchange formulation) which has been experimentally applied successfully to earth but not taken into GCM for reasons veiled in fog. An attempt for Venus has been started but given the dense atmosphere is very hard to do, incomplete. A simple version might be a different matter.

    This correctly ignores static fields (do nothing) and deals in actual energy flow between entities.

  3. Konrad says:

    Robert Brown writes a good response at Digging in the Clay, however this –

    “and the Earth’s climate is particularly pernicious given that it involves two fluids, not one, where one of the two absolutely dominates the surface area of the planet, the heat content of the planetary surface, the source of all feedback associated with the strongest greenhouse gas, the source repository of the vast majority of the second strongest greenhouse gas, and a major fraction of both the latent heat transport within and albedo variation of the other fluid — and it isn’t the atmosphere and is rather poorly understood or incorporated into climate models.”

    – would have to rate as the understatement of the century.

    The entire AGW question can be solved with the answer to one simple question –

    “given 1 bar pressure, is the net effect of the atmosphere over the oceans cooling or warming of the oceans?”

  4. Trick says:

    Konrad 10:21pm – “The entire AGW question can be solved with the answer to one simple question – “given 1 bar pressure, is the net effect of the atmosphere over the oceans cooling or warming of the oceans?””

    The top post linked Robinson & Catling Dec. 2013 Letter has your answer.

  5. Roger Clague says:

    The Robinson and Catling model uses lapse rate, pressure and optical depth.

    Lapse rate and pressure are thermodynamic concepts. Optical depth is a radiation concept.
    The radiation concept is not necessary.

    The atmosphere is not a “grey body”. That is one to which Black-body laws can be applied.

  6. Gail Combs says:

    Dr. Robert Brown of Duke wrote, a for me, more understandable comment over at WUWT:

    http://wattsupwiththat.com/2014/05/26/quote-of-the-week-howler-from-the-world-meteorological-organization-what-warming/#comment-1648000

    rgbatduke says:
    May 28, 2014 at 10:21 am

    ….This isn’t the right question. The question is, “What is the absorption cross-section for a 15 micron photon”. That’s the effective surface area intercepted by each CO_2 molecule. It is large enough that the mean free path of LWIR photons in the pressure-broadened absorption bands of CO_2 in the lower atmosphere is order of a meter. That means that LWIR photons — whatever their “size” — with frequencies in the band go no more than a meter or few before they are absorbed by a CO_2 molecule.

    The lifetime of the excited state(s) is much longer than the mean free time between molecular collisions between the CO_2 molecule and the (usually nitrogen or oxygen or argon) other molecules in the surrounding gas. That means that the radiative energy absorbed by the molecule is almost never resonantly re-emitted, it is transferred to the surrounding gas, warming not just the CO_2 but the oxygen, nitrogen, water vapor, argon as well as the other CO_2 molecules around. Periodically CO_2 is thermally excited in-band by just such a collision and radiates energy away, but it is not like an elastic scattering process such as occurs in specular reflection within clouds. In band/thermal radiative energy gradually diffuses upwards, with the mean free path of the photons increasing the higher one goes, until it starts to equal the remaining depth of the atmosphere and photons emitted “up” have a good chance of escaping, cooling the molecules (on average) that emit them. It takes order of 100s of absorptions and emissions for radiation to diffuse upward to escape, and there is an almost equal probability that radiation will diffuse downward (especially from the lower levels) where we observe it as back-radiation/greenhouse radiative forcing of the surface.

    Even this is oversimplified. Because of pressure broadening, molecules close to the ground emit photons “in the wings” at frequencies that less broadened molecules at higher altitudes/lower pressures are nearly transparent to. That means that there is a steady CO_2-mediated “leakage” even from lower altitudes directly to space from the edges of the monotonically decreasing-with-height absorptive bandwidth. It also means that there is a MAJOR change in atmospheric absorptivity/emissivity with simple high and low pressure centers as they move around, as well as a modulation of the size of the emission-wing “hole”.

    Grant Petty’s book can walk you through much of the physics.

    If I read this correctly, CO2 WILL absorb the IR photons in the correct wavebands but the overwhelming ‘reaction’** is for the energy to be transfered to the rest of the atmospheric molecules warming them. At that point, since hot air rises the energy is carried up. Of the small number of CO2 molecules that do emit a photon instead of transferring energy via a collision, a second ‘reaction’ is for the excited CO2 to emit at frequencies “in the wings” half of that energy escapes through the emission-wing “hole”. Therefore the “Downwelling radiation” from CO2 is a tiny fraction of the amount the Climastrologists are claiming. AND since “LWIR photons — whatever their “size” — with frequencies in the band go no more than a meter or few before they are absorbed by a CO_2 molecule,” additional CO2 in the atmosphere means diddly squat.

    ‘reaction’** I am a chemist and that is the only term close to what I mean that I can think of.
    ……

    Oh and while you are at it read the first couple of comments between Nick Stokes, A.W. and Janice.

    A.W.’s comments:

    Nick Stokes says: @ May 26, 2014 at 9:02 pm

    “Gosh, you’d think they’d check the data”

    What data? They are simply making a perfectly valid statement about CO2 increase and the forcings. You can measure and talk about CO2 concentration without getting into temperature issues.

    REPLY: Oh, bullshit, you left out this part: “the warming effect on our climate – over the decade 2002-2012″. Nick Go obfuscate the truth someplace else. Now I’m SURE you are a paid troll. – Anthony

    Janice Moore says: @ May 26, 2014 at 9:05 pm

    Hey, Anthony! Great minds, heh, heh.
    #(:))

    REPLY: Yeah, Nick either can’t help himself, as his many years of working for CSIRO has produced an institutionalized reaction to anything contrary to the monthly newsletter, or he’s simply paid to come here and sow obfuscation. Given he’s often one of the earliest commenters for anything contrary to his world view, I expect he has a trigger mechanism setup to alert him so he can derail threads early on with his particular brand of diversion.

    Bottom line: increased CO2 forcing with no resulting increase in temperature, means no warming, and WMO believes there was warming. Bad science, just PR – no cookie. – Anthony

    Oh MY, and that was a month before the Steven Goddard kurfuffle.

  7. Trick says:

    Roger Clague: “Optical depth is a radiation concept.The radiation concept is not necessary. The atmosphere is not a “grey body”. That is one to which Black-body laws can be applied.”

    The attenuation of solar energy in an atmosphere IS necessary part of atm. thermodynamics of energy transfer. As Robinson & Catling write p. 12 in word then follow up with the basic math:

    “Infrared opacities are grey, that is, described by a single, broadband optical depth, tau IR, at every pressure level. Solar radiative transfer occurs in stratospheric and tropospheric channels.”

    They explain how planet atm.s can become near isothermal with height creating a stratosphere above tropopause observed by pressure transition to lower than ~0.1 bar and increased transparency to IR. Whereas at higher pressures below tropopause atm.s become opaque to thermal radiation causing gas temperature to increase with depth and convection to ensue. The math is developed to clearly support the usual imprecise words of science.

    Thus the radiation concept is necessary explanation for observations. Isothermal temperature profile with height when increased in temperature from above where little to no convection ensues in stratospheres. Non-isothermal profiles observed in troposphere where increased in temperature from below where vigorous convection ensues.

  8. Roger Clague says:

    Trick says:
    June 30, 2014 at 1:28 pm

    Whereas at higher pressures below tropopause atm.s become opaque to thermal radiation causing gas temperature to increase with depth and convection to ensue.

    Remove the phrase ” opaque to radiation” and you are left with

    Higher pressure causes gas temperature to increase.Which we all agree on.

    “opaque to thermal radiation ” is the mechanism of the energy transfer needed to maintain the temperature difference due to gravity.

    We do not need to consider radiation to calculate surface temperature. We need tropopause temp and lapse rate.( -g/c )

    Convection plays almost no part in the cause, formation or maintainance of the lapse rate

  9. Trick says:

    Roger 8:33pm: “We need tropopause temp… “

    Which is necessarily established by and calculated with energy conservation for radiative energy transfer in balance with convective and conductive energy transfer. At some point on the lapse curve, you need calculate or measure an intercept temperature since all the g/Cp supplies is the slope (rate of change).

  10. gallopingcamel says:

    Robert G. Brown and I were colleagues in the Duke University physics department for a dozen years. When it comes to physics in general and thermodynamics in particular I trust his judgement way above my own.

    However, I have spent several decades working with lasers (producing radiation from 2 microns to 11 MeV) so I am more inclined to argue with him when the subject is radiative transfer equations.

    Robert made some comments on my “Titan” post at “Digging in the Clay” that sounded rather negative so I tried to set up a meeting with him in the first week of June to sort things out. Unfortunately he was traveling that week but as noted by “Gail Combs” he published something at WUWT that supports my opinion that Trenberth’s “CO2 Forcing Theory” is nonsense owing to the fact that Earth’s troposphere is opaque to radiation in the 15 micron band.
    http://wattsupwiththat.com/2014/05/26/quote-of-the-week-howler-from-the-world-meteorological-organization-what-warming/#comment-1648000

  11. gallopingcamel says:

    Stephen Richards, June 29, 2014 at 4:49 pm:

    “Before making a post I reach out to experts in the field. For example, Tom Peterson (GHCN), Albert Klein Tank (KNMI), Richard Alley (Penn State).

    Blimey, that’s a cabal of geniuses :)”

    From my perspective those are the “Good Guys” along with Denning, Nikolov and Zeller because they are ready to engage with the general public that pays their salaries. Even though they may not agree with us they do not claim that the “Science is Settled”.

    The “Bad Guys” are folks like Kevin Trenberth, Michael Mann, Jay Severinghaus and Thomas Stocker. They know they are peddling “Junk Science” but they act as if their ideas are revealed truth. Here are some issues that cause these people to disengage from the public and “Lawyer Up”.

    1. Kevin Trenberth’s theory that CO2 delivers 4W/m-2 per doubling of CO2 concentration.
    2. Michael Mann refusal to correct his paper that has the Tiljander sediments inverted.
    3. Thomas Stocker knows that CO2 lagged temperature for the last 800,000 years.

  12. wayne says:

    I sure like both Gail and Peters responses above and thanks to Gail for including RGBs comment I seemed to miss… that near the surface, the lw emitted by the surface in the co2 bands is mostly absorbed before it even reaches your nose. On that point, it is the same results I have found, not 100% for radiation in gases bow to optical depths but the vast majority is absorbed right in front of you.

    So what difference will it make by doubling the co2 concentration and now the surface ir in the co2 15 micron band (about 13.5 to 17 microns) is then absorbed before it reaches your belly button? After all, there is only so much being radiated in this band per second and it is all immediately absorbed. As Gail said there is then inter-atmosphere emissions/absorptions which of course occur but this form of very short radiative transfers falls more in Fourier’s realm of energy transfers for those transfers are merely a portion of the thermal diffusion coefficient of the particular gas composition at this scale.

    This is one of the major reasons I no long feel co2 has anything to due with surface temperatures, next to zero, and my investigation into Venus, Jupiter, Titans atmosphers seems to agree with this stance. GC, still enjoying your link to Robinson and Catling work for it has greatly helped me get over a problem I had hit when addressing Titans atmoshere specifically.

  13. tallbloke says:

    GC: http://wattsupwiththat.com/2014/05/26/quote-of-the-week-howler-from-the-world-meteorological-organization-what-warming/#comment-1648000

    So what are the takeaway implications of Roberts comment?

    Upwardly directed emission events from co2 molecules in the lower atmosphere have a longer mean free path than downward.
    But the vast majority of emission events result in the warming of non-radiative molecules and water vapour.
    This means buoyant convection is the primary means by which energy in the troposphere heads upwards towards space.

    Is that right?

    Robert Brown’s comment in full:

    The question is, “What is the absorption cross-section for a 15 micron photon”. That’s the effective surface area intercepted by each CO_2 molecule. It is large enough that the mean free path of LWIR photons in the pressure-broadened absorption bands of CO_2 in the lower atmosphere is order of a meter. That means that LWIR photons — whatever their “size” — with frequencies in the band go no more than a meter or few before they are absorbed by a CO_2 molecule.

    The lifetime of the excited state(s) is much longer than the mean free time between molecular collisions between the CO_2 molecule and the (usually nitrogen or oxygen or argon) other molecules in the surrounding gas. That means that the radiative energy absorbed by the molecule is almost never resonantly re-emitted, it is transferred to the surrounding gas, warming not just the CO_2 but the oxygen, nitrogen, water vapor, argon as well as the other CO_2 molecules around. Periodically CO_2 is thermally excited in-band by just such a collision and radiates energy away, but it is not like an elastic scattering process such as occurs in specular reflection within clouds. In band/thermal radiative energy gradually diffuses upwards, with the mean free path of the photons increasing the higher one goes, until it starts to equal the remaining depth of the atmosphere and photons emitted “up” have a good chance of escaping, cooling the molecules (on average) that emit them. It takes order of 100s of absorptions and emissions for radiation to diffuse upward to escape, and there is an almost equal probability that radiation will diffuse downward (especially from the lower levels) where we observe it as back-radiation/greenhouse radiative forcing of the surface.

    Even this is oversimplified. Because of pressure broadening, molecules close to the ground emit photons “in the wings” at frequencies that less broadened molecules at higher altitudes/lower pressures are nearly transparent to. That means that there is a steady CO_2-mediated “leakage” even from lower altitudes directly to space from the edges of the monotonically decreasing-with-height absorptive bandwidth. It also means that there is a MAJOR change in atmospheric absorptivity/emissivity with simple high and low pressure centers as they move around, as well as a modulation of the size of the emission-wing “hole”.

    Grant Petty’s book can walk you through much of the physics.

  14. Roger Clague says:

    tallbloke says:
    July 1, 2014 at 8:13 am

    What does Robert Brown say about the role of convection in energy transfer in the troposphere?

    Brown supports the radiative-convective hypothesis. According to this model, convection is an important factor in transferring energy and maintaining the lapse rate.

    Light enters at 3 x 10power10 m/s. Convection moves at say 10 m/s.Therefore convection cannot be a factor in maintaining the lapse rate.

    Convection is caused by the lapse rate.
    The lapse rate is cause by gravity and maintained by radiation.

  15. Trick says:

    tb 8:13am clip: ”Is that right?”

    rgb is explaining the basics from Grant Petty text in words with no specific cites. That book’s basic physics are in agreement with Robinson & Catling (R&C) 2013 basic physics shown in math in the attached SI and summarized intro.:

    “Here we use a simple, physically based model to demonstrate that, at atmospheric pressures
    lower than 0.1 bar, transparency to thermal radiation allows short-wave heating to dominate, creating a stratosphere. At higher pressures, atmospheres become opaque to thermal radiation, causing temperatures to increase with depth and convection to ensue.”

    This is in basic agreement with lab test as cited as far back as in Callendar 1938. Seems to me any discussion of planetary atm. thermo. physics in attempt to further understand nature must be shown by precise math in compliance with these imprecise basic words.

    Unless one has found an issue with the basic math. In that case, a cite to eqn. number in Robinson & Catling 2013, Petty text as amended, and/or Callendar 1938 is useful & sound analysis/reasoning must be provided rather than simple assertion. The scientific method is way more interesting tool & useful for advancing understanding nature than an asserted view or politics.

    So e.g. tb asserts: ”Upwardly directed emission events from co2 molecules in the lower atmosphere have a longer mean free path than downward.”. Examine this:

    tb: Is there an eqn. for mean free path in Petty, R&C, or Callendar 1938 you used to figure this out? The reader could then do confirming research or the author. To get a point across the author really needs to demonstrate the reasoned analysis work backed by cited experiment otherwise it is better just read basic original cites in Petty, R&C and/or Callendar 1938 to better understand & discuss nature. rgb would improve by citing them also by eqn. number.

    ******

    Roger asserts 11:40am: ”Convection is caused by the lapse rate. The lapse rate is cause by gravity and maintained by radiation.” R&C 2013 deals with convection & lapse. Here is a cite p. 12, do you agree? If so, then why not just clip from the top post. If not, which eqn. is an issue?

    “Tropospheric convection follows a dry adiabat adjusted by an empirical scaling factor typically around 0.6-0.9 to match an observed mean moist adiabat in each atmosphere. The ratio of specific heats at constant pressure (cp) and volume (cv ), respectively, sets the dry adiabatic lapse rate, and is 1.4 for atmospheres dominated by diatomic gases, such as those considered here.”

  16. tallbloke says:

    Trick: So e.g. tb asserts: ”Upwardly directed emission events from co2 molecules in the lower atmosphere have a longer mean free path than downward.”. Examine this: tb: Is there an eqn. for mean free path in Petty, R&C, or Callendar 1938 you used to figure this out?

    No, it seemed to me to be a fairly trivial deduction from what Robert said;

    “Because of pressure broadening, molecules close to the ground emit photons “in the wings” at frequencies that less broadened molecules at higher altitudes/lower pressures are nearly transparent to. That means that there is a steady CO_2-mediated “leakage” even from lower altitudes directly to space from the edges of the monotonically decreasing-with-height absorptive bandwidth”

  17. Trick says:

    tb 8:03pm – Well, I’d have to consult his ref.d Petty text to try figure out his meaning in precise math eqn. from imprecise words:

    “…less broadened molecules…”

    What is a broadened molecule, how does it become less broadened – how is that noted in math exactly? Units? Can you write out the fairly trivial deduction formula you used for me?

    “..molecules…are nearly transparent to.”

    How is a molecule transparent? There is a trivial formula you used to deduce that?

    ” a steady CO_2-mediated “leakage” “

    What is leaking exactly? How is it determined to be steady? What does “mediated” mean in math?

    “..absorptive bandwidth”

    How is bandwidth absorptive? This one just doesn’t compute enough to ask more of a question. If it is trivial to deduce, please fill me in.

    Reading Robinson & Catling top post & Petty text is way more clear. Radiative energy transfer is not intuitive to be trivially deduced IMO (the R&C SI is not trivial). Though some write on blogs as if it were trivial.

  18. tallbloke says:

    Trick: try figure out his meaning in precise math eqn. from imprecise words:

    Maths is a useful technique in the toolbox of science. It is not science itself. Science is concepts linked and validated by experiment, quantified by measurement and formalised by equations derived by mathematically capable physicists, biologists and chemists. This formalism is at the end of the chain of understanding, not at the beginning of it.

    Words are used to express scientific concepts, and are fully adequate if you understand what they refer to.

    “broadening” in this context refers to the wider range of wavelengths a molecule can absorb energy from when subjected to higher pressures. This has been validated experimentally. I don’t need to lay out the experimental data and algebraic derivations in order to use the concept.

  19. Roger Clague says:

    Trick says:
    July 1, 2014 at 5:21 pm

    R&C 2013 deals with convection & lapse
    and asks which eqn. is an issue?

    My problem starts with the title, “dependant IR transparency” is not needed. It is added on to give the impression this is a radiation theory.

    R and C 2013 use this equation

    optical depth = constant x pressure

    The aim of the model is to recreate the lapse rate. But pressure does that without referring to optical depth.
    If you are serious about radiation theory you use Beer/Lambert Law, or SB laws of emission and absorption.

    You can’t use pressure as an input and call it a radiative theory

    Convection is too slow to be an important factor in a model of energy transfer in the atmosphere.

  20. Trick says:

    tb 8:28am: “This formalism is at the end of the chain of understanding, not at the beginning of it.”

    Depends on one’s talents & abilities as shown by history.

    M. Faraday for example was near totally an experimentalist spending long hours in the lab nearly working himself to death. Not having been schooled in the theory, Faraday learned it only after seeing the experiment work as intended. He got help inventing anode, cathode terms for instance. His “electrotonic” field was not precisely understood until Maxwell’s ability to work with formulae proved out the EM field theory with math.

    Heinrich Hertz experimentally proved EM field waves bidirectional in 1888 in a very dark room using a simple step Faraday had not thought about now Hertz had ref.d Maxwell’s theory.

    If you read R&C carefully, their introduction is formed into words by parsing thru the eqn.s in their SI. In that sense, for R&C at least the formulas came first before the intro. was written.

    I observe the answers to many debates around here are addressed & settled in that R&C Letter. I wish it & its eqn.s would be ref.d more.

    ******

    Roger 10:49am & tb: “..use Beer/Lambert (B-L) Law..You can’t use pressure as an input and call it a radiative theory”

    Pressure and Planck radiation distribution were joined at the hip by Schwarzschild.

    Linear B-L for a thin slab of atm. is a starting point function of atm. density to find optical path integrating B-L over the attenuation length of a single wavelength beam in a single direction.

    Nature’s differential optical depth d(tau IR) then becomes a summed function of d(pressure) (R&C eqn. S16) invoking the atm. hydrostatic assumption eqn. S15. This generalizing B-L over many wavelengths (Planck Function) turns B-L into the more general Schwarzchild eqn. allowing for scattering integrated over all directions.

    R&C discuss this in S2 and S3 of the SI, more formally developed in online notes Caballero Chapter 5 or Petty text CH2&3. See Caballero eqn. 5.40 for simple B-L and 5.57 for generalized Schwarzschild eqn. So pressure IS tied directly into Planck radiation theory by the hydrostatic eqn. since the macro. atm. is found to be in hydrostatic equilibrium.

    Once you go thru R&C S2 and S3 dead nuts, Caballero more formally uses the plane parallel approximation to put into irradiance math tallbloke’s “Upwardly directed emission events from co2 molecules in the lower atmosphere have a longer mean free path than downward” as a function of Planck radiation distribution and optical path. One can then use that math to calculate irradiance by inserting actual numbers.

    For irradiance difference up & down, see Caballero 5.61 for the irradiance flowing upward across some atm. level z and eqn. 5.66 the downward irradiance. R&C suggest the answer will depend on if you are in their stratosphere or troposphere “channel”.

    I will let you or tb do the work or due diligence research since you seem interested. This stuff is NOT intuitive nor is it easy to discuss precisely and correctly in blog format. You need the eqn.s. I predict will get different answers to net irradiance for each “channel” but that is speculative until I see the work out proof.

  21. tallbloke says:

    Trick: R&C suggest the answer will depend on if you are in their stratosphere or troposphere “channel”.

    I already knew this from what Robert Brown wrote (in words). Which is which I specified lower atmosphere in my summary (in words).

    If you read R&C carefully, their introduction is formed into words by parsing thru the eqn.s in their SI. In that sense, for R&C at least the formulas came first before the intro. was written.

    The concepts came first, then the analysis of the data, then the formalism of the equations, and then, finally the write-up submitted to the journal.

  22. Trick says:

    tb – “I already knew this…”

    I would submit you & rgb are predicting or speculating on the outcome rather than “knew this” and whether it being different in the “channels” – as am I if none of us has run thru the math (or found a worked example in Petty or elsewhere) with real observed planetary atm. numbers. It is tough math I can appreciate the difficulty. Intuition could well be wrong.

    In reading about M. Faraday’s experimental work, as he became well known many people showed up to offer their input & he was challenged to sort out the ideas with which he should spend time. It was sorting just one of those that indeed caused him to return to the lab after a 2yr. time out to recover from overwork exhaustion. The test proving EM field was the result.

    Post-grad.s get to calculate emissivity of materials to prove they can do it & understand it. Under one particular challenging Prof., they are set up with a test sample where it is known emissivity comes back greater than 1. Since that is drummed in as impossible, they are observed fretting about mistakes, not wanting to tell about or even believe their results.

    Gotta’ do the tests, gotta’ run the reasoned analysis numbers to show understanding & agreement with test.

  23. tallbloke says:

    Trick: Radiation is always going to have an easier time travelling through a less dense, lower pressure medium.

  24. Trick says:

    tb 9:08pm: Take a look at R&C eqn. S16 sum for differential optical depth tau IR I mentioned. Kappa sub i is the grey opacity of ith unique source (absorbing gas) & depends on T and p. w sub i is the mass mixing ratio. Then dp/g factor. So yes pressure counts as well as other factors.

    The composition of an atm. is shown to be important as well as the density. IOW, radiation might have an easier time traveling thru an atm. with lower kappa & w at a higher rho or p. This is a bone of contention at times on blogs and is quickly explained by examining the math & is a reason R&C mention atm. composition in the very 1st sentence.

    This is a very concise Letter that can be used for many explanations IMO.

  25. Here is a quote from “rgb” that goes to the heart of the idea that CO2 provides a “forcing” by returning radiation to the surface that would otherwise be radiated into space:

    “The lifetime of the excited state(s) is much longer than the mean free time between molecular collisions between the CO_2 molecule and the (usually nitrogen or oxygen or argon) other molecules in the surrounding gas. That means that the radiative energy absorbed by the molecule is almost never resonantly re-emitted, it is transferred to the surrounding gas, warming not just the CO_2 but the oxygen, nitrogen, water vapor, argon as well as the other CO_2 molecules around.”

    The radiation captured by CO2 in the lower atmosphere (troposphere) is transferred to surrounding molecules just as convection, conduction and phase change do. Robinson & Catling’s physical model says the temperature gradient should be -g/Gp except where vapors are present (Earth and Titan).

    The thermal IR radiation that makes it into space is radiated mainly from the cloud tops, the tropopause and the stratosphere. The troposphere contributes very little owing to its opacity to thermal IR.

  26. Roger Clague says:

    Trick says:
    July 2, 2014 at 9:28 pm

    The composition of an atm. is shown [ in R and C 2013] to be important as well as the density.

    However Rand C 2013 say their findings are ” despite great differences in atmospheric composition”

    In R and C 2012 they say
    “Model atmospheres are assumed to be in hydrostatic equilibrium” Hydrostatic equilibrium means gravity creating a pressure/temperature/ density gradient.

    The R and C model is a gravity/pressure model,and is similar to the N and Z model.Remove all references to optical depth and it still works. It is called radiative/convective to get funding.

    gallopingcamel says:
    July 3, 2014 at 4:20 am

    In the quote by Brown, he seems to say C02 does not re-emit. Which is wrong.

  27. Trick says:

    gc 4:20am: Yeah, many authors write in words how the radiative energy transfer occurs in single absorption/emission and collision processes. Then they show some details.

    It is very hard to be intuitive about these individual detail events since we cannot see them so resort to macro observations for our intuition. R&C merely treat this basic physics with: “As pressure-broadening or collision-induced absorption applies generally to (optically) thick atmospheres…”

    ******

    Roger 9:49am: “Remove all references to optical depth and it still works.”

    What is “it” that still works? The intent of the Letter is to form a solid math basis for: “..at atmospheric pressures lower than 0.1 bar, transparency to thermal radiation allows short-wave heating to dominate, creating a stratosphere.”

    Removing the explanation for transition from optical thick to optical thin transparency at tropopause near z height where 0.1 bar occurs ~min. T profile, the Letter is gutted. It is not intuitive that 0.1 bar is roughly the common tropopause transition and the math helps explain the process well enough for reasonable application to distant sun/planet/moon systems once their solar sw/orbits and rudimentary atm. details are observed.

    ”…(rgb) seems to say C02 does not re-emit. Which is wrong.”

    Note rgb writes “almost never” as opposed to “does not”. Other authors have written prose for the explanation to, I will look around for one if in copy & paste text & then post up as found.

  28. gallopingcamel says:

    Roger Clague said:
    “In the quote by Brown, he seems to say C02 does not re-emit. Which is wrong.”

    “rgb” did not say that. He was pointing out that as pressure increases it becomes increasingly likely that an excited CO2 molecule will give up its excess energy via collisions rather than radiation.

    While radiation transfers energy rapidly through a transparent medium it becomes a pitifully slow process when the medium is opaque. To take an extreme example it might take 20,000 years for a photon generated by a nuclear reaction in the Sun’s core to emerge from the photosphere.