Can you explain this "pot lid" hypothesis for the atmosphere?
I was just reading an interesting study about climate feedbacks. From the abstract:
"Omission of these density shifts amounts to a major flaw in the doubled-CO2 forecasts that have been made to date. The large forecast rise in sea level temperature, and the positive water vapor feedback common to all GCM’s, are both shown to be artifacts of the hydrostatic approximation. As much as 65 to 80 percent of the consensus forecast rise in sea level temperatures appears to be due to modeling errors."
What do you think "hydrostatic approximation" means here?
Later on in the feedbacks section:
"Then when additional CO2 is introduced, temperatures rise. If water vapor is allowed to be taken up, given the same starting conditions, temperatures rise much faster.
The error introduced by the hydrostatic approximation is subtle. The incorrect physics do not matter in a relatively static scenario, without any imposed warming trend, for there is no density signal to be lost. However, if more CO2 is introduced, then as the sea level air gets warmer, the air in the models is stuck between the ‘pot lids’ and cannot move up or down."
Do you understand this concept of a "pot lid"?
This study seems to challenge to the positive water vapor feedback hypothesis. The author has chosen not to submit to peer review (see conclusions). What do you make of all this?
What a pain in the a!s!s:
- DaveHLv 510 years agoFavorite Answer
Here is a de-cyphered link
Edit. Having just read the essay.
The 'pot lids' are described in detail in this section of the document.
"4 The hydrostatic approximation prevents density shift"
What this paper suggests is that 'all' GCM's use an incorrect assumption. The GCM's model the atmosphere as a series of rings around the earth, each at increasing altitude. The paper says that the models do not acknowledge movement of air between these rings. i.e in each altitude band the air is constrained. Thus, when air expands by being warmed this expansion does not move to the next layer up, it is constrained as if by a 'pot lid'.
This has an additional consequence in the model. As air is warmed and expands, since the 'pot lid' in the model does not permit vertical transfer, the pressure will increase. In response to the pressure increase there will be a further increase in temperature (compressing a gas causes it to warm).
The paper says that this additional, but incorrect, heating is applied at each atmospheric layer in the model, as each layer has its own 'pot lid'. This effect is shown in the diagram on page 13.
It will be interesting to see how this essay is reviewed.
edit gcnp. Re "As near as I can tell he assumes that pressure goes up with warming. That is not correct". I think he's saying that IN THE MODELS the pressure in each atmospheric layer goes up... hence an additional assumed increase in temperature. It would be interesteding to find out if this is actually the case. This should be discovered by any responses to the essay.
edit gcnp & AMP. I'll re-read this if I get time. But as I understand he's not saying 'this is how it works' he's saying 'this is how the models resolve it'... and the essay was quite specific saying that ALL models work this way. i.e. with compartmented layers of atmosphere.
- JimZLv 710 years ago
It was an interesting article and another good example of the large number of variables that are extremely complex and poorly understood.
I am not sure what it is referring to. If you cook a stew, the heat and water vapor will mostly remain in the pot until enough pressure pushes the pot lit up and a little steam leaks out. I think this is referring to what happens before the leak where the heat and vapor are trapped. I believe that is what it probably referring to when it refers to "hydrostatic" based on my interpretation of his abstract. Presumably it assumes that the heat and density is trapped near the surface.
The only other analogy I thought of was if you can’t get it done then get off the pot. The only difference is that the latter analogy deals more with methane than CO2 (just kidding in case someone thought I was serious)
- 10 years ago
Dave H: I have very high doubts, like gcnp58, that such an effect has been applied in the models. Without reading the essay in full depth yet, my first question would be if he has considered that it is not necessary for layers to share air vertically - volumetric expansion up would counteract the temperature response in a non-bounded atmosphere. This is indeed what we see with warming layers, take for example the observation of the heightening tropopause.
That being said, it would have been of the utmost prudence for him to actually reference specific models and their behavior, instead of guessing as peg miner said and then leaving the actual modelers to waste their time with bald assertions. This paper doesn't need addressing unless he can actually support his point.
Col: The order of events was pegminer giving a straight-forward answer to the question, kapaakid (now "Kono Kohako") calling him a pothead, and then pegminer accusing him of not knowing what "aloha" means because he used the word - which has heavy associations with love and respect - in tandem with a baseless and petty (not to mention pointlessly aimed) insult.
BTW, in case you're too new to this forum (just judging off your account age), kapaakid doesn't have the most stellar (shall we say) record for being civil. Don't defend childish behavior.
- 10 years ago
This paper does seem to challenge the basics of C02 atmospheric dynamics, and certainly the positive water vapor feedback hypothesis, however, there is significant research which should be undertaken to demonstrate that it actually occurs as described. Interesting stuff, hopefully we can see more of this type of thinking translated into meaningful research.
pegminer: why should you care how someone (kapaakid) writes? And, yes he did use "aloha" correctly.
PS, after spending several tours in Hawaii, I do know what a JAFH is.Source(s): col
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- pegminerLv 710 years ago
I'll explain what the hydrostatic approximation is: it says that vertical accelerations are small compared to the acceleration of gravity. It is an excellent approximation for the atmosphere as a whole, but not for a place like a strong thunderstorm.
Do you have a reference to a published paper that describes these "pot lid" ideas? I don't really care to read some paper by unknown authors off an unknown link.
The snippet that you quote implies that you can't have vertical motions under the hydrostatic approximation--that is not true. You just don't have large accelerations, so that the air column is always in hydrostatic balance, dP/dz =- rho*g , but you can have vertical motion. Perhaps the authors of your paper don't fully understand the hydrostatic approximation.
EDIT: In atmospheric dynamics (and oceanography too, for that matter) the hydrostatic approximation is exactly what I said it was--nothing more, nothing less. After taking a look at this "paper," I think that the author not only does not understand the hydrostatic approximation, I don't think he has a good understanding of numerical models of the atmosphere, either. If you look at his paper you'll notice that he doesn't reference a single book on numerical weather or climate prediction, instead apparently preferring to just guess at what is actually done in climate models. If he believes he has a brilliant, unrecognized insight into numerical modelling of climate and weather, why doesn't he just create a model and run it?
- Anonymous10 years ago
So, the author has chosen not to submit to peer review. That is a good clue. "Hydrostatic approximation" is probably just gibberish. The hydrostatic equation is about the increase of pressure with increasing depth due to the gravitational force on water. Nothing more and nothing less.
"Pot lid" sounds like whatever the above author has been smoking.
- gcnp58Lv 710 years ago
It's wrong. As near as I can tell he assumes that pressure goes up with warming. That is not correct. pressure remains constant and determined by atmospheric mass, more or less. That is why his density plot is wacky. Another way to put it is that he should be running his thermodynamics for constant pressure and using the heat capacity of a gas for constant pressure. The atmosphere doesn't have a lid. Period.
p.s. Think about what he says logically. If he were correct, and warm humid air was more dense, pilots would *love* taking off in Denver when it was 100 F and 95% humidity. But they don't. When it's like that the air is less dense and they go back to the gate and throw the fat people off the plane so they use less runway.
@DaveH: Nope. His figures of density change are wrong. Warming air doesn't increase the density, it decreases density. Ask any pilot, would they rather take off on a cold day or a hot day? The only way you get density to increase like that for warming is to let pressure increase with temperature, but that's not how the atmosphere works. It's Cp, not Cv, he even admits that because he argues the volume changes. The proposition that GCMs and atmospheric modelers are ignorant of such a basic property of atmospheres is absurd, and only someone in deep deep denial of climate change would give this more than the minute of inspection it deserves.
I understand the skeptics want some facet of climate physics to be wrong, but it's not. They all need to argue policy, not the science, since guys like this make them look ignorant and delusional.
- Anonymous10 years ago
It's another admission that their models have to stink because there's no way to make a good one.
It's also an admission that they really don't know.
- Hey DookLv 710 years ago
Perhaps your broken link has failed some new YA lie detector test. Good. Read what Pegminer says here instead. He is a real scientist, unlike your pseudo science blogger phonies. In fact, read ANY science for a change, instead of spending your life BSing here.