Discussion > An experimental demo of GHE.
Something feel bad about averaging that insolation across the 4 faces.
Also... as we've already discussed... the speed of rotation might mean that each face
does not have time to reach thermal equilibrium before being plunged into darkness.
But a 4 face problem is far easier to model.... so have at it.
TheBigYinJames
Innocent question: why not take this discussion to a physics forum where people with the necessary background will be able to help?
BitBucket
Because discussion of global warming is (understandably) banned on the physics forum I use occasionally.
Martin A
Also it's more fun, and gives you a better grasp of a physical effect if you can arrive at it through your own efforts. Science being portrayed as something only experts can do is part of the problem with the politicisation of climate science. Science always has been, and should always be about a logical path that non-specialists can follow to the logical conclusion.
You may have to be a specialist to invent it, but should not have to be a specialist to understand it.
TheBigYinJames
Very well said, TBYJ. And that doesn't of course preclude checking one's working with any other physicist at a later stage.
Richard Drake
Martin and Yin, you are my two favorite commentators here, so I take much of what you say seriously (non-emotive stuff anyway). But, without in any way meaning to offend (really), I have no idea whether you have sufficient physics backgrounds for your comments on the physics of GHG or any other climate science issue to be definitive or even solid. The fact that Martin asks SoD for guidance on physics issues implies to me that he is not himself a physicist. Other commenters, ditto, with bells on.
Saying that one "...should not have to be a specialist to understand it", is a bit naive; sure, if you trained as a physicist, that might be true. But for non-physicists that is highly unrealistic. One might be able to follow each step in a series of equations or an argument, but being able to spot fallacious arguments is quite another matter.
Sure, physicsforums.com blocks climate science questions, but there are other newsgroups.
BitBucket
Dung, What is an IRag ?
RKS, please forget my LH2 idea, it was daft. I think that the ceiling could be a copper sheet, thermally bonded to a heat exchanger of the same power as the lamps.
What would we expect to see as the CO2 was added to 200ppm, 400ppm, 800ppm, etc. It is only if all sides of the discussion make predictions of the state of the system before the experiment is carried out that the results would be useful. If this was the case I think that it is cheap enough and easy enough for a university to put it together in a few months.
Roger Longstaff
BB. No I'm an engineer. But that involved enough on quantum theory and modern physics for semiconductors and nuclear ( and to read as much further as I desired). Plus electromagnetic theory (needed for microwaves etc) plus the classical physics stuff to a second-nature level. Plus concepts that are simple but can be hard to get to grips with if never studied formally - statistical equilibrium and so on.
I asked on SOD about where often-quoted results in Climate Sciencs had come from - not to explain basic principles.
The greenhouse gas stuff would have been 1st year physics for engineers stuff (photons, black body radiation, interaction with molecules) etc Which is why I find it staggering that ex NASA engineers (Dragon Slayers) write total bollocks on the subject - if they'd taken a UK engineering course in the 60's, they'd have failed their 1st year exams. I only assume their work was not key to getting Apollo into orbit around the moon.
That said, please find the basic errors that an A-level student would laugh at, in my Jan 7, 2013 at 6:32 PM posting on this thread.
Martin A
And ditto for me BB, not a physicist, but have studied physics and maths at university undergraduate level as part of an electronics materials and systems degree, albeit a long time ago, as well as having read widely in the subject and kept myself numerate. It doesn't make me a physicist.
I take your point that the 'slayers' don't accept my physics credentials, but then science is not about credentials, it's about what you can prove from first principles and experimental results. There is far too much arguing from authority in this arena already.
TheBigYinJames
Martin, best guess: the four sides are not in equilibrium, since 3/4 of the time they are not facing the sun. But maybe the fast spin rate is supposed to counteract that. Only a guess though...
BitBucket
I think a more realistic model is going to the left from the front face
1 side is facing the sun and is warming towards equilibrium, not never getting to it.
2 side has just been in sun, and is cooling furiously
3 side is cooler still but rate of cooling slower
4 side is almost in thermal equilibrium with the cosmic background
So none of the sides are in thermal equilibrium, but cooling at a rate which is be mostly governed by the heat capacity of the solid I would imagine.
TheBigYinJames
As on the other thread, I prefer a disc to a sphere.
Bitbucket, we are having fun here. Bouncing ideas, no final arbiter, no pretension, no authority figure. I doubt we could do that on a physics forum. If we wanted, we could go to Tallbloke's. But discussions take place there at a rather higher level than I feel able to participate in. Why would you even think of getting us to move? You don't have to read it if you know we are nothing but a bunch of (mostly) amateurs.
rhoda
BB, BYIJ,
I should not have said the rapidly rotating planet is in equilibrium. Thanks for pointing this out.
What I meant to say is that each of its faces is essentially constant in temperature.
A face faces the sun for ¼ of theperiod of rotation, during which it warms. It then faces space for ¾ of the period of rotation, during which it cools. But the rotatation is so fast that the cooling while a side faces away from the Sun is negligible - 1 degree? (just making a value up) and the warming while it faces the Sun is also neglible - the same 1 (?) degree.
So the temperature of one of the four illuminated faces is constant with a very small ripple imposed on it and it can be analysed to a very close approximation as if it really were constant.
Martin A
BB, just shut up. Who give a stuff about your meta-analysis?
shub
Shub: I may have missed something but I was enjoying BB's contributions and his/her interaction with Martin and Yin. If you really think it's worth it, please identify what you consider meta-analysis so that I know what I shouldn't be giving a stuff about. (And I'm interested, in passing, in whether Martin has found BB easier of late. But this may not be time or place.)
Richard Drake
Rhoda, getting you to move? Not at all, I just made the mistake of thinking that you wanted an answer. A physics forum would be a logical place for that.
As you say, I don't have to read it and mostly I don't. The GHE, misnamed or not, is settled science. It surprises me that your scepticism would lead you to that subject. I mean once you start doubting the GHE, an effect accepted by physicists for ages, and instead seem keen to hitch your horses to a theory believed only by a few oddballs, you leave the realms of scepticism for that dark land of the d's that shall remain unnamed.
BitBucket
BitBucket:
The GHE, misnamed or not, is settled science.
Bad term to use, the old SS. It's the best theory we have is how I'd put it. And what TBYJ was I think saying is that by working at a few aspects from first principles one learns more about how strong it really is. I added that one would then check stuff (if it hadn't already fallen apart) with other physicists. I expect the GHE to come through this test. I take the old view that it's the “enhanced” greenhouse effect where the real debate lies (see also here). And I have to say this contribution, with its cutesy allusion to deniers, is not as enjoyable as before.
Richard Drake
richard
I think BB's post above answers your question to me, pretty well. By the way, it would be nice if you pick on the anonymous Bitbucket and the zeddeadbed, for their anonymity.
shub
Shub, see here, where one of your nominations is in a wide-ranging group of four. I've been inclined to follow Jonathan Jones on BB; the latest contribution, as I've already said, gives pause for thought. But surely you're not expecting me to go into my view on this at length on this thread? Point me somewhere it's on topic, please, if you want to discuss further.
Richard Drake
I don't want you to go into your views on the matter. I want you to pick on them. It doesn't have to be sustained. It doesn't have to be here. You intervened on BB's behalf, when his 'contribution' (your words) consisted of trying to propose cordoning off a discussion in which he has zero contribution otherwise.
shub
An excellent thread on the role of GHG's and LW radiation [note the increased IR window from 40Wm^2 to 66Wm^2 now allowed by Trenberth reducing the net warming role of GHG's to zero]
There are a lot of comments working in detail through the processes involved but very informative in relation to GHE. Well worth bookmarking.
http://tallbloke.wordpress.com/2012/12/14/emissivity-puzzle-energy-exchange-in-non-vacuums/
RKS
Another example of the 'Atmospheric' Greenhouse Effect due to mass, gravity and insolation, as opposed to the 'Radiative' Greenhouse Effect schoolchildren and students have been indoctrinated with since the 70's, where they forgot all about The Ideal Gas Law. This is, after all, how stars are formed with insolation being supplied by the 2.7K cosmic background temperature.
http://www.universetoday.com/35664/temperature-of-the-planets/
RKS
RKS - Does average temperature depend on speed of rotation?
"In our paper, we discuss (among other things) the effect of rotation on the mean surface temperature of a planet. The short answer is this: rotational speed (...) cannot impact the mean temperature. (...)..
- Ned "That's as up to date as I can get until the paper is published.
Jan 7, 2013 at 1:36 PM RKS
RKS - to follow up on this, I think Ned and co are wrong in general. I don't know if you saw my Jan 7, 2013 at 6:32 PM posting
A Tale of Two Planets, Qubi-stat and Qubi-spin.
Cubic planets that rotate in 90° jumps, with only one face facing the sun at any instant, are not typical of planets in general. However, they can be analysed precisely, as I have done* [subject to any errors I may have made]. In the particular case I looked at, the mean temperatures work out as follows:
Very slow rotation: 62K
Very fast rotation: 173K
Although you obviously can't apply the result for a cubical planet rotating in 90° jumps directly to a spherical planet rotating continuously, it does strongly suggest that the average surface temperature depends on the rotational speed even for non-cubical planets.
As I've said before, this is a consequence of the nonlinearity introduced by the T^4 relation. As soon as you start taking averages when there are nonlinearities lurking you can get results that seem counter intuitive.
Does this all make sense?
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* I talked about the fast-rotating planet being in equilibrium. What I meant to say is that it is in thermal steady-state, the temperature of each face being essentially constant ie constant with a small ripple superimposed.
Martin A
(And I'm interested, in passing, in whether Martin has found BB easier of late. But this may not be time or place.)
Jan 8, 2013 at 12:39 AM Richard Drake
Yes, BB obviously went through quite a bad patch not long ago. But it seems that he's back to his normal well-balanced self now, at least so far as the external world is concerned.
Martin A
Martin A: Hold off making a new thread? Absolutely. And thanks.