If you are still in this thread, I just had a question involving what might be an amusing coincidence: I was reading a paper today for my real job on light concentrators from 1990 by G. Smestad et al and noticed that the authors acknowledged one “George E. Smith of HP” in the acknowledgements section. Of course, I know that there is likely to be more than one George E. Smith in the world, but given the circumstances seemed similar enough (someone working in industry on some sort of physics-related stuff) that I was wondering if that might actually be you!?!

http://ceos.cnes.fr:8100/cdrom-98/ceos1/science/dg/dg19.htm

If emissions are equal to absorption would not oxygen excited by collisions re-radiate that energy in these peak absorption bands?

That is what I recall reading but have not been able to recall what the source was.

Larry

For example, relativistic charged particles travelling very close to (c) upon crashing into a solid media; say a Cesium Iodide crystal, suddenly find themselves travelling faster than the local velocity of light (c/n), so if for no other reason they have to slam on the brakes, and during that braking deceleration you get Bremsstrahlung radiation which IS a cointinuous spectrum of “braking radiation”, which I think is the literal translation of Bremsstrahlung. Anna v is probably an expert on this stuff; I only remember it from my days messing around with scintillation detectors; although I used Anthracene and Stilbene Crystals instead oc CsI, since I was interested in Neutron detection; and my Po/Be neutrons always came with tons of gammas. We were too poor to be able to get Pu/Be neutron sources; not to mention that unmentionable word.
But somehow, I don’t think atmospheric IR radiation can be regarded as Bremsstrahlung of a sorts.
George

George,

From Pierrehumbert’s ClimateVol1.pdf:
“A Nitrogen molecule N2 in isolation does not interact to any significant extent with infrared light; one might think that collisions do not change this picture, as N2 has no lines to be broadened by collisions. “”"

Thanks Igl; so Peter Humbug to the rescue !

Well I always wondered what the source of thermal (hot body) radiation was whether BB or “pseudo BB”, because I knew it couldn’t be an infinite sequence of line spectra and somehow have anything like that Planck spectral behavior. Don’t remember which of my books pointed out that any material body has at least electric charges, which undergo accelerations as a result of the “molecular” temperature.

You have to remember that my graduation day was 52 years ago; when there wasn’t any quantum chromodynamics; hell the “8-fold way” was the cats meow. And to add insult to injury; ALL of my High school and college textbooks went into a box that supposedly went on a boat, but a month later, it failed to come off that boat on the Manhattan docks; so I have had to go by memory mostly since then; replacing only those that had any pertinence to my work needs which wasn’t much in the high tech industry.

Maybe 90% of what I learned in school was never ever used in my daily work; so there’s some cobwebs in there I know.

I’m intrigued by that transient supermolecule concept though. The lay public doesn’t know how much stranger than fiction the truth really is; maybe that’s what keeps me going.

George

Without negative feedback some values should grow continuously. So, if there has been a proven positive relationship between rising CO2 levels and rising temperature in the past, rising CO2 levels should have caused the increase of temperature “for ever”.

It’s easy to see why that’s incorrect. An increase in forcing (e.g. due to raised greenhouse gas levels) doesn’t cause an increase of temperature “for ever”. More likely it results in an increase in temperature towards a new equilibrium temperature.

Leave a pan of water in you kitchen which is at constant temperature. The pan will settle to a pretty constant temperature. Now move the pan onto the top of your central heating boiler. A constant forcing is being applied to the pan. Does it cause an increase of temperature “for ever”? No. The temperature rises towards a new equilbrium temperature. Are negative feedbacks required to stop the “value grow(ing) continuously”. No.

From Pierrehumbert’s ClimateVol1.pdf:
“A Nitrogen molecule N2 in isolation does not interact to any significant extent with infrared light; one might think that collisions do not change this picture, as N2 has no lines to be broadened by collisions. Nonetheless, during the time a collision is taking place the pair of colliding molecules momentarily behaves somewhat like a more complex four-atom molecule, which has transitions that can indeed absorb and emit infrared radiation. This leads to collision-induced absorption, whose associated absorption coefficient is generally a smooth function of wavenumber. Because of the lack of line structure, such absorption is referred to as a continuum. There are many possible processes through which collisions can induce absorption. The collision can impart a temporary dipole moment to a rotation or vibration that ordinarily had none, allowing it to absorb or emit a photon. The collision can break a symmetry, allowing transitions that are otherwise ”forbidden”
by symmetry principles”
So maybe you are 10% right :-)

George E. Smith (08:56:56)

“But I was not talking about those absorption spectra (other than that they exist); I was talking about the thermal emission spectrum of those gases;…”

The two types of spectra are identical, as far as the frequencies of absorption/emission. I don’t want anybody to get the idea that gases absorb at discrete frequencies and emit as blackbodies. They don’t. “”"

Well I think I’ve restated enough that nothing emits like a black body.

The paper cited by Igl above contains a whole lot of meteorological stuff that is outside of my knowledge base; so I’m not able to comment intelligently on that. I notice he does mention “continuum radiation” from water; as well as line spectra.

But for the moment I will just accept that gases don’t emit any thermal radiation; despite the fact that every text book I’ve ever seen particularly on infra-red technology have all stated that every single thing in the universe emits thermal radiation due to its temperature; and yes I accept that nothing in the universe emits black body radiation.

I would like to know just what that water “continuum radiation” is though; and what causes it.

By the way; Kirchoffs law only relates to a body that is in thermal equilibrium with its surroundings at a given temperature; well I suppose my textbooks are wrong on that too.

I wonder why the sun seems to emit a “continuum ” radiation, even though it isn’t solid or liquid; well I suppose plasmas do contain accelerating electric charges.
And for the record I’ll repeat; no not all thermal radiation spectra are blackbody spectra; but they are thermodynamically limited to radiate less than a BB (at any wavelength); well at least that’s what my textbooks say.

Ahh, foinavon, here it is:

(a link to a blog page)

What say you?

Nope, jae, that doesn’t address the point.

Lindzen made a very specific prediction. At a time when tropsopheric moisture content variations were not easily assessed, he predicted that moist (cumulus) convection, which is expected to increase with atmospheric warming under enhanced CO2 concentrations, would result in a drying of the upper troposphere. This proposed drying would be a negative feedback that would partly offset the positive feedback from enhanced water vapour at lower altitudes.

When it became possible to determine tropospheric moisture content relaibly, and assess the response to greenhouse-induced warming, it became cleat that Lindzen’s hypothesis was incorrect. The upper troposphere desn’t “dry” in in response to tropospheric warming….in fact it “moistens” (much as models predicted, as it happens).

Your blogger doesn’t address this point at all. He speculates (rather discursively) about all sorts of other things. But these don’t relate to the Lindzen hypothesis which was sufficiently specific that it could be assessed categorically by real world measurements.

Does this description represent the balance over just the land mass, or an average over the land mass and the oceans combined? If just the land mass, then it seems it would be very different over the oceans, and if this is just the land mass then can you post something explaining the balance over the ocean?

Your humble gardner.

“But I was not talking about those absorption spectra (other than that they exist); I was talking about the thermal emission spectrum of those gases;…”

The two types of spectra are identical, as far as the frequencies of absorption/emission. I don’t want anybody to get the idea that gases absorb at discrete frequencies and emit as blackbodies. They don’t.

George Smith 15:22:16

“So the ordinary atmospheric gases DO (sorry about the caps foinavon) radiate thermal radiation solely as a function of their temperature, and since they radiate a black body spectrum, and not a line spectrum, only a portion of that radiation is in the absorption band of say CO2 or other GHG such as water.”

George, thank you for the refresher. However, gases don’t radiate a blackbody spectrum. Their spectrum is composed of thousands of discrete lines, each with its own emissivity. Here is a low resolution absorption spectrum for the atmospheric gasses. The upper panel indicates the blackbody spectrum at the indicated temperatures.

Solids and liquids may often be approximated as blackbodies, but obviously anything that has visual color cannot be a perfect blackbody. “”"

OK so perhaps I should have said “continuous spectrum” rather than “Black Body”. Yes I know about black grey, red, and blue bodies; and that no real body is a black body but some come close.

I believe I used the term thermal radiation.

The Wiki reference you gave (very nice plot thanks) is all about absorption spectra. It doesn’t say a thing about thermal radiation spectra.

The word “Thermal” generally implies thew concept of “Temperature”; and I believe I said that the thermal radiation was solely a function of temperature.

Now all of the ABSORPTION spectra in your Wiki post are either atomic or molecular (mostly) absorption spectra; they are a unique p[roperty of an individual molecule, or an individual atom.

No individual atom or molecule, has any idea what you are talking about when you mention the word TEMPERATURE; it is not a property of individual molecules or atoms.

Now I agree with Joel, that N2 and O2 don’t absorb in the long wave infrared. sorry for the mixed attribution there Joel.

Those absorption spectra are line spectra, and the intrinsic line specra are broadened by effects such as Doppler shifts, which are a result of the kinetic energy of the molecules themselves in a gas; which is a function of temperature (E=kT). The intermolecular collisions which are a function of total molecular density (pressure) also result in line broadening. The shorter the time interval between molecular collisions, the bigger is the energy shift. (Heisenberg ? maybe dE.dt > h/2pi )

So I don’t disagree that the absorption spectra of those molecular or atomic species in the atmosphere are line spectra which have to be explained in quantum mechanics, as westhighlander implies (or one might infer from his comments.

But I was not talking about those absorption spectra (other than that they exist); I was talking about the thermal emission spectrum of those gases; which depends roughly on the 4th power of temperature (yes I agree no real body is a true black body); but the BB spectrum bounds their possible thermal spectrum at the same temperature.

If we want to resort to quantum chromodynamics to explain global warming; we would need more space, and formatting and font capability than Anthony’s fireside here.
Then we might as well use Einstein’s general relativity, rather than Newton’s gravity or Keppler’s laws of orbital mechanics to explain the seasonal changes in climate.
We don’t need a 500# bomb to swat a fly. But Westhighlander’s comments do remind us that we can get a long way removed from “climate sensitivity”, or “forcings”, or any of the other trappings (like “anomalies”) that pass for science in the field of “Climatology”.

I believe that the Japanese recently described that as “ancient astrology”; and that might be unkind to the ancient astrologers.

But I shall have my own bookburning, and do some warming myself by setting fire to “The Infrared Handbook” of Wolfe and Zissis, and “Elements of Infrared Technology” by Kruse, McGlauchlin and McQuistan, along with all my optics and quantum electronics texts; and learn to rely on Google and Wikipedia for the gospel truths. And I need a new Handbook of Chemistry and Physics that contains all those new sciences like forcings.

This is not surprising as once one gets a Ph.D. hood for work in physics the Prof. whispers to you the “Secret of / to the Universe” — Unfortunately I can not divulge this to the uninitiated (under the pain that the Universe will just collapse back into the …… and disappear) and as for the rest of those of us who have been initiated — well we already know it.

What I can do however — is drop a few oblique hints that may be illuminating (pardon the pun?)

1) Let’s start with an everyday experience — Look at your self in a mirror — no physicist can explain to anyone else how you can see yourself — or any coherent image for that matter (except by reverting to classical Electromagnetism)

2) In point of fact while QED (Quantum Electrodynamics) is considered to be the most validated theory that we have ever constructed — no closed form Quantum equation can explain in detail the energy levels of any atom except hydrogen (even H requires some fudging let alone what happens when you shine a photon on a H2 molecule) — even Helium (monatomic gas) is a problem — let alone a triatomic molecule such as CO2 or H2O

3) We do even worse when we have to consider more than one molecule or atom of the same species in a very rarefied gas (with only elastic collisions) let alone when we mix gases

4) Now let the atoms have some inelastic collisions — things rapidly become a hand waving exercise — left to the reader

5) Now if we let the gas molecules have some center of mass motion (temperature) when absorbing and reradiating then the Doppler effect starts to change the effective energies of the transitions and of course the individual molecules are also exchanging CM energy in their collisions

6) Skipping ahead a couple of graduate courses — Some of the absorption and reradiation transitions can be “forbidden” in the case of an isolated atom or molecule due to the “wrong quantum numbers” — however, when you let atoms collide and the other “funny stuff” — the transitions just might become allowed

7) some of the atoms or molecules can carry some of the excitation energy (due to photon absorption) with them when they move a considerable distance (particularly at low densities where because of the low probability of collisions (long mean free path) and the low probability of the transition (long effective lifetime) of the state (so-called metastable) — now they can appear somewhere else a long way from where they absorbed and already ready to radiate

8) there is a lot more and we are just trying to explain how a monochromatic beam of photons can pass through an isolated column of gas

9) Note nothing has been said about oceans, ice caps, clouds, aerosols, cosmic rays, solar magnetic fields, breaking waves, or any of the other things which make this an interesting topic

PS: — everything we treat in physics is considered a “closed systems” — in reality — perhaps the Universe is a “closed System” — But nothing else is