Monday, May 10, 2010

The very dry, very adiabatic lapse rate

Over at the real Pielke Sr. web site aka Tony Watts plays scientist, Steven R Goddard misunderstands what the dry adiabatic lapse rate is and tries to claim that the hothouse Venus is strictly a gravitational effect. Nick Stokes and Leonard Weinstein try and set him right. The Bunny got a comment through (after a considerable delay) but Watts is blocking Eli's further words of wisdom over there, and besides the same thing has broken out on moyhu and Real Climate, where Richard Steckis touched it off

The essential argument is that the heating of the Venusian atmosphere occurs through adiabatic processes and not through absorbance of IR by GHGs.

[Response: Since 'adiabatic' means without input of energy it seems a little unlikely that it is a source of Venusian heating. - gavin

Comment by Richard Steckis — 7 May 2010 @ 12:19 PM
and
Stephen Baines says:
7 May 2010 at 10:44 PM

“@ RS “As for Gavin’s comment re: pseudo-science, I guess it is only pseudo-science when it disagrees with your pre-conceived ideas about Venusian climate.”

If by preconceived ideas, you mean ideas conceived and tested by scientists over more than a century of prior research, I think he would agree.”

A century of research can be toppled by one expirment. So do no hang your petard on the fallacy that a century of research is an unbreakable bulwark of truth.

[Response: If you think a century of science is going to be toppled by obviously ignorant blog posts on WUWT, you are very mistaken. There is a big difference between coming up with new insights that cause a reevaluation of current paradigms and just getting very basic physics wrong and misapplying completely other bits of physics. Goddard and Motl are engaged in the latter, not the former. - gavin]

Comment by Richard Steckis — 8 May 2010 @ 9:22 PM

There is more but you get the feeling, so let Eli have his say.

It's called the dry adiabatic lapse rate, which means that it is an idealization where the energy flow into and out of any packet of air is balanced. That is what Gavin was getting at.

The surface temperature is fixed by a radiation balance between incoming solar and out and incoming IR. The second, colder endpoint is some place up there where something else happens to break the adiabatic condition, for example ozone absorption starting to kick in at the top of the Earth's troposphere. For a planet with an atmosphere and no greenhouse gases, pretty much the temperature of space.

That leaves gas rarification/compression driven by gravitation as the mechanism for setting the atmospheric temperature profile. It is not saying that radiative energy flow is negligible, just that it is balanced.

What does the lapse rate determine? Looking at extremes is useful. If the surface is at absolute zero the thickness of the atmosphere (at least for an ideal gas) would be zero. What if the surface were at infinite temperature. Then the height of the atmosphere would be infinite also. From this, we conclude that the height of the atmosphere is determined by the lapse rate and the surface temperature

There are, of course, a few other things to consider. First, the dry adiabatic lapse rate is not 10 K/km for every atmosphere. For example it is 4.5 K/km on Mars and 2.0 K/km on Jupiter. Better put it is the ratio of the local gravitational constant divided by the specific heat (in J/(kg-K) or g/Cp. For the case of Venus, where the surface and the atmosphere are very hot, we have to account for the contribution of molecular vibrations to the specific heat, which will change with temperature and thus with altitude.

The lapse rate does not set the surface temperature, which is determined by the solar radiation absorbed at the surface and the IR re-emitted by greenhouse gases in the atmosphere.

End

31 comments:

J Bowers said...

Eli, shouldn't it read 'Steven Goddard', not 'Richard'?

Anonymous said...

Speaking of WUWT, here's a keeper (or should I throw him back?)


Dave McK says:
May 9, 2010 at 1:37 am

The surface of Venus is dominated by volcanism. It has a crappy heat pump to lose the heat.
About 80% of the planet consists of a mosaic of volcanic lava plains, dotted with more than a hundred large isolated shield volcanoes, and many hundreds of smaller volcanoes.
Volcanoes less than 20 kilometres (12 mi) in diameter are very abundant on Venus and they may number hundreds of thousands or even millions.

Forget about greenhouse, dude. You aren’t helping.


--caerbannog the anonybunny

EliRabett said...

Oh no, we treasure such stuff here at Rabett Run

Anonymous said...

Fish here

Actually, Steven Goddard is involved in an exercise to confuse the witless masses. He's not claiming that the greenhouse effect plays no role in the temperature of Venus. He's engaged in a a smoke and mirrors campaign to deny the importance of the effects of CO2.

Goddard writes as a response to a comment:

[i]Leonard Weinstein

You are correct.

Earth already has plenty of greenhouse gases, so my point is that even if earth went to 100% CO2, the maximum temperature increase would be less than 36C – nothing like Venus. (In reality, it would get cooler because of the loss of water vapour.)
[/i]

Steve Bloom said...

IMHO it's a waste of time commenting over there. The damage is done in the posts themselves since that's all most readers see.

Codeblue said...

Snipped from WUWT
_____________________________
stevengoddard says:
May 10, 2010 at 3:19 pm

What I am saying is that because of the high pressure on the surface of Venus, adiabatic heating causes the very high temperatures. Those kinds of temperatures aren’t seen on earth because of the lower pressure.
________________________________


Gentlemen, there is no negotiating with a madman.

Arthur said...

Of course Goddard is nuts, but I think we don't generally explain this (the relative influence of radiation and convection on the atmospheric temperature profile) well. Eli's attempt up above ("looking at extremes ...") is not very satisfying because there's an element of circular reasoning - surface temperatures are determined by *both* radiation and convection, not by radiation alone, and not by convection alone. How to explain this clearing without confusing the masses? I don't claim to have a solution... nothing I've tried has worked either...

Rattus Norvegicus said...

I think the good Dr. Inferno offers a cogent summary of Goddard's argument.

Neven said...

Thanks, Rattus Norvegicus, now I thoroughly understand what Goddard is doing.

Thomas Palm said...

The idea that the heating of planets has nothing to do with greenhouse gasses and only with the pressure of the atmosphere pops up now and then. For example Hans Jelbring wrote an article in Energy&Environment v 14 p 351 2003 titled "The Greenhouse Effect as a Function of Atmospheric Mass".

J Bowers said...

Dale Husband also has a take on Goddard's sad attempt to gain genius status, entitled 'Idiocy on WUWT!'.

http://circleh.wordpress.com/2010/05/08/idiocy-on-watts-up-with-that/

EliRabett said...

Arthur, in the tradition of some models are useful, Eli really does not think that adding convection to the stew gives folk much of a hold on what the dry adiabatic lapse rate is.

Yes, convection is important, but the goal is to convey understanding. Technically you can discuss the lapse rate w/o including convection on a simple basis, or including it on a more complicated one.

Arthur said...

Eli - but convection is the reason for the lapse rate. A non-convecting "atmosphere" (for example, one frozen solid) would not be restricted to the lapse rate temperature gradient.

The very rough way I see it is:

* convection results in the lapse rate up to the tropopause
* GHG's determine the height of the tropopause

but that's not entirely correct either.

carrot eater said...

I think this is a little cumbersome and confusing, Eli. You've tackled the issue better before.

Why not start with a closed packet of air, and consider what happens if the air above it is warmer, or colder?

Horatio Algeranon said...

The real mystery is why people with no clue generate so much attention.

Horatio has taught junior high students with a better understanding of physical science than many (if not most) of the folks who post at WUWT.

Anonymous said...

Here is a great example of "denier science" -- a "denier derivation" of the atmospheric lapse rate (From http://www.tech-know.eu/NISubmission/pdf/Politics_and_the_Greenhouse_Effect.pdf)


I. The high school approach.
The average sea level pressure is around 1013 mbar. If you live at a higher altitude the
pressure will be less. Your barometer at 100 m above sea level will read about 12 mbar less.
Pressure is a direct measurement of how much atmospheric mass there is above your head per
square meter. The ideal gas law can be written PV = RT where P is the pressure (Pascal), V is
the volume (m3), R is the gas constant (Joule/K) and T is the average temperature (over some
days). Let us now calculate the temperature in a 1 m3 volume at any height. Hence T = P/R, T
is proportional to P and P is known from observation to decrease with increasing altitude. It
follows that the average T has to decrease with altitude.


So the author takes the Ideal Gas Law, sets n and V to 1, and from that he computes a lapse rate! Constant values for n and V will of course give us a constant density (independent of pressure). This is a revolutionary new concept in atmospheric science -- modeling the atmosphere as an incompressible ideal gas!

"Denier science" is just *too* much fun!

--caerbannog the anonybunny, who wishes he could get a 100K+/year gig at a wingnut "think"-tank publishing stuff like this.

Anonymous said...

The "parcel method", meteorology 101. Watts should know that, as should Goddard. They should also know what and adiabatic process is and what the DALR is.

Eli " The lapse rate does not set the surface temperature, which is determined by the solar radiation absorbed at the surface and the IR re-emitted by greenhouse gases in the atmosphere.

Exactly, even bright bunnies in high school know that.

MaplLeaf

Anonymous said...

Eli, Arthur,

there is quite an easy way to demonstrate the idiocy of the adiabatic heating. In its basic version, physics are totally dispensable. Just tell the folks the following:

Consider, we climb up a mountain. As everybody knows, the temperature will decrease a rate of about 1°C/km. [No further explanations here. Nobody will have a problem]

Now let's consider a cold day in February. At sea level, the temperature is, say, 0°C. The air pressure is about 1 bar. It is certainly colder at the top of our mountain, and 10 km above sea level there will be some frosty –10°C. [Keep the maths as simple as possible]

And now consider a hot day in July. At sea level, the temperature is, say, 30°C. The air pressure is about 1 bar. 10 km above sea level, the temperature will be approximately 20°C.

It is evident that the air pressure at sea level has not changed and does not determine the temperature at sea level. It's the sun, among other things. It is evident that the air pressure explains just the difference between the different altitudes.

If somebody asks about the exact relationship between the latter, well, then you have to proceed. However, if the Venus does not disprove greenhouse warming, 99.9% of all human beings quickly lose their interest in weird adiabatic processes.

Mickey, Minnie, Mighty, or Fred.

seamus said...

FTFA: "Because we have a sun providing energy to the periphery of the atmospheric system, the atmosphere circulates vertically and horizontally to maintain equilibrium. Falling air moves to regions of higher pressure, compresses and warms."

This is the greatest revelation in atmospheric science ever. The sun's energy gets applied at the top of the atmosphere? Which causes convection? I sort of had the impression that sunlight goes through the atmosphere and heats the surface, which heats the air at the surface (causing convection).

--

Adiabatic \Ad`i*a*bat"ic\, a. [Gr. 'adia`batos not passable]

(Physics) Not giving out or receiving heat.

Note: The adiabatic expansion of carbon dioxide from a compressed container causes the temperature of the gas to decrease rapidly below its freezing point, resulting in the familiar carbon dioxide "snow" emitted by carbon dioxide fire extinguishers.

Adiabatic line or curve, a curve exhibiting the variations of pressure and volume of a fluid when it expands without either receiving or giving out heat.

Flavius Collium said...

The mistakes seem to be made at an even more basic level, confusing energy and power. Power is the energy flow rate.

If you *compress* an ideal gas in a thermos bottle, it heats up.

If a gas *is* at high pressure, it is not necessarily hot or cold.

Anonymous said...

It is foggy here this morning but the Average Global Temp.; is shooting up like crazy man---It is gonna burn off sooner than you think?
Not that, that has to mean anything, just check out how a picture can be worth a thousand bucks...

http://thebenshi.com/2010/05/10/37-photoshopped-polar-bear-is-the-climate-science-community-really-really-really-this-clueless-yes/

It may seem long but it is short, gotta jet now---vrooooom, there I go!

Hank Roberts said...

http://basicinstructions.squarespace.com/storage/2010-05-09-politics.gif?__SQUARESPACE_CACHEVERSION=1273454286276

carrot eater said...

chris colose took a crack at explaining it all. pretty well, I think.

Lumo said...

Dear Rabbit,

some remarks about your cute arguments are here.

Thanks, Richard Steven Motl

Arthur said...

Wow, Motl claims:

"The lower portions of the atmosphere are only heated adiabatically, by convection, as the circulating gas warms up as it drops down and gets compressed, and by heat conduction."

and even further on:

"In the same way, the solid interior of the Earth is warming up by 30 °C per kilometer (near the surface, where you can still find some fast enough and adiabatic circulation of the lava etc.) and going up to thousands of degrees [...] and this fact is gravitational in origin, completely independent on the emissivity of the rocks in the infrared spectrum."

Ironically Gerlich and Tscheuschner in their reply article also deny that the greenhouse effect has any bearing on Venus. But I wonder if they will attack Motl for so blatantly violating the second law of thermodynamics in his explanation?

But overturning basic physics and geophysics should win you some sort of prize... Any mice out there with suggestions?

a_ray_in_dilbert_space said...

One wonders if Lubos took any real physics classes when he was in grad school. There is certainly no evidence that he retained any of the material.

Marion Delgado said...

a-ray:

Lubos does "Conservative Physics" now. Says so right at the masthead of the Reference Frame.

He pioneered it. Before him, there was just physics. But that had a frame of data-gathering, peer review, a consensus on what the data meant, etc.

In another frame of reference - seen through a tea-bag, for instance, you do physics by first vetting your researchers for Marxist bias - for instance, do they accept that market forces keep planes in the sky? if not, fire them - then providing them with conclusions and assigning them each micro-tasks that build towards the conclusion.

Motl is literally the greatest conservative physicist ever to live. I try to type softly in his presence.

Lumo said...
This comment has been removed by the author.
Mark said...

More brilliance from Motl, speaking about a hypothetical planet with a pure nitrogen atmosphere: "The huge thermal radiation of the surface would escape into space without any suppression because the atmosphere would be completely transparent. Because this would be much bigger output than the fixed incoming solar energy, the whole atmosphere would be cooling: it couldn't stay in any "nearby" stationary state."

So the outgoing energy is greater than the incoming energy? I'm trying to determine whether Motl has discovered a perpetual motion machine of the first kind or the second kind.

exusian said...

What is Motl's problem? He's much too young to have 'gone emeritus'.

Anonymous said...

"As we have mentioned, the 300,000 times higher CO2 concentration on Venus, relatively to ours, means that they're just 18 CO2 doublings above our levels which only adds 20 °C or so (there are no H2O-related feedbacks over there worth talking about). You know, powers of 2 increase very quickly (2^18 = 262,144), so the logarithms of large numbers are still reasonably small."

Look - Motl doesn't know that the logarithmic relationship of CO2 doesn't hold over all concentrations. Isn't that cute! The arrogant physicist betrayed by his ignorance, once again.

See Figure 1: http://journals.ametsoc.org/doi/pdf/10.1175/1520-0469%281977%29034%3C0448%3AARCMSO%3E2.0.CO%3B2

-M