- To my recollection, the derivation of Planck's Law was always referenced to the interior of an enclosed cavity. That's why one German term for blackbody radiation is Hohlraumstrahlung (hollow space radiation). There is no "background" radiation in an enclosed cavity.
- Notwithstanding your repeated claim that the law is valid only for a 0 K background, this is neither consistent with observation, nor is it consistent with the observed fact that radiation emitted BY any body isn't influenced by the radiation incident ON that body.
- Physicists have been using Planck's function in the standard way long before climate scientists got involved. There is no inconsistency between climate scientists' use of it and astrophysicists' use of it.
- CJ's understanding...is simply wrong. It is experimentally wrong. It is theoretically wrong. It is amazingly wrong.
- CJ is right in one narrow sense: the SB law isn't two-way because it is UNDERSTOOD by anyone who actually works with radiation to apply only to the radiation EMITTED by a surface. If you want the two-way exchange between two plates with different temperature, you apply the SB law to each plate separately to get the component of the flux emitted toward the other flux.
- This is not climate science. This is routine undergraduate-level physics.
- Don't take climate scientists' word for it. Ask any competent astrophysicist.
Prof Petty is not answering my question, but refers to some unknown astro-physicist. Not very helpful. I think Prof Petty should be able to answer himself. Like Judy Curry he seems to refer to undergraduate students.
Surprisingly, Prof Petty acknowledges that I am right in stating that SB expresses one-way net flow, and not the difference of two-way gross flow. Surprisingly, Prof Petty thus seems to agree with me on the essential point. Yet he expresses very clearly that I am all wrong. It does not make much sense, to me.
Prof Petty has a only a vague confused recollection of Planck's derivation of his radiation law, and has not understood that the radiation from the cavity representing the blackbody, is radiation into a background at 0 K.
Prof Petty believes that the SB law of astrophysics is the SB law of climate science, and does not appear to understand that there is an important difference between the radiative net exchange of Sun-Earth and that of Earth-atmosphere, because the Sun is very hot and very far away.
So I repeat my question Prof Petty:
- Which is the original scientific source of the SB law you are using in your climate science?
- From now on, I will only debate the correctness of "standard" radiation physics with those who prove that they are at least familiar with those basics -- and with the applicable terminology -- at the level of the first 8 chapters of my introductory book.
- You are welcome to insist that something in those 8 chapters is wrong, but you'd better be prepared to point out specifically what you think is wrong, at the earliest point where it appears in the development, and why you are so damned sure it's wrong. And then we can go from there.
- Otherwise, it's like debating the physics of flight with someone who's never seen an airplane.
OK, I repeat my question about the source of the SB law. I think it is a fair question on a central problem.
It is funny that Prof Petty wants to discuss the physics of flight with me. Maybe he has (not) read my work on this topic:
- The Secret of Flight (book)
- The Mathematical Secret of Flight (article)
- The Mathematical Secret of Flight (talk).
Inlägg
You really are extraordinarily tiresome. This Professor Petty has the patience of a saint to have given you the responses he has. Your knowledge of the physics is woeful and it's obvious that you will refuse to learn, no matter how carefully it's explained to you.
SvaraRaderaAstrophysicists indeed know very well about mid-infrared emission from the atmosphere. They launched IRAS, ISO, Spitzer and Herschel after all. No doubt you believe that we could do mid-infrared astronomy from the ground and didn't need to launch all those expensive space missions.
I have posed a simple question to Petty and expect an answer. Yes, it is tiresome to pose a simple question over and over without getting any response.
SvaraRaderaHere is the answer to your simple question.
SvaraRaderaI use the Stefan-Boltzmann law, whose original source is
Stefan, J.: Über die Beziehung zwischen der Wärmestrahlung und der Temperatur, in: Sitzungsberichte der mathematisch-naturwissenschaftlichen Classe der kaiserlichen Akademie der Wissenschaften, Bd. 79 (Wien 1879), S. 391-428.
(My translation: "On the relationship between thermal radiation and temperature")
and
Boltzmann, L.: Ableitung des Stefan'schen Gesetzes, betreffend die Abhängigkeit der Wärmestrahlung von der Temperatur aus der electromagnetischen Lichttheorie, in: Annalen der Physik und Chemie, Bd. 22 (1884), S. 291-294
(My translation: "Derivation from electrogmanetic light theory of the Stefan Law as regards the dependence of thermal radiation on temperature")
But I don't need to actually go to those original sources, because the SB law immediately follows from the Planck function by integrating over both solid angle and wavelength. In fact, homework problem 6.7 in my book asks the student to show that the SB constant, sigma = 5.67x10^-8 is given exactly by
sigma = 2 pi^5 kB^4 / 15 c^2 h^3
where kB is the Boltzmann constant, c is the speed of light, and h is Planck's constant.
Do you need original sources for the Boltzmann constant, the Planck constant, the speed of light, or pi? If so, I'm sure if you apply yourself a little, you can track them down.
SvaraRaderaAnd since it is likely that you will insist on an original source for the Planck function, it is
Planck, M. (1900). On the theory of the energy distribution law of the normal spectrum, Verh. Dtsch. Phys. Ges. Berlin, 2: 202, translated into English in ter Haar, D, (1900), The Old Quantum Theory, Pergamon, Oxford UK, pages 79-81.
and Planck, M. (1900). Verh. Dtsch. Phys. Ges. Berlin, 2: 237. Translated into English in ter Haar, D, (1900), The Old Quantum Theory, Pergamon, Oxford UK, pages 82-90.
Of course, I don't actually go to the original source for the above, as Planck's function is well-documented in countless books since then, don't you agree? I'd be surprised if many practitioners go to original sources for any of the very well-established relationships that they work with, such as Maxwell equations, Newton's Laws of Motion, Einstein's mass-energy equivalent and the like. Or do you see a problem with this?
But my work doesn't depend only on Planck (which is to be preferred to SB unless you know you're dealing with something that can be idealized as a blackbody or at least a graybody -- a poor assumption for serious atmospheric radiative transfer except in special cases). I also use Kirchhoff's Law, which says that monochromatic emissivity equals monochromatic absorptivity for an isothermal system in local thermodynamic equilibrium. Are you going to need a reference for that too, Mr. Johnson, or are you capable of looking it up yourself?
SvaraRaderaThen there's also the Beer/Bougert/Lambert Law for monochromatic transmittance:
transmissivity = exp(-[optical path])
where optical path = integral_s1^s2 beta(s) ds
Multiple sources (hence the multiple names) -- can you please look them up yourself, or do you need me to help you?
Conceptually (as regards atmospheric radiative transfer in a non-scattering atmosphere), everything I require beyond the above basic laws can be directly derived from Kirchhoff's law and Beer's law, including for example the so-called Schwarzschild Equation:
dI/ds = beta ( B(T) - I)
where I is the monochromatic radiant intensity (units of W/m^2 per steradian per unit wavelength), beta is the absorption coefficient (units of inverse length), and B(T) is the Planck function at the wavelength in question.