Guest essay by Jan Kjetil Andersen
As Willis describes in his article on December 21, the atmosphere can be seen as a gigantic heat engine, i.e. a machine which convert thermal energy, namely temperature, into mechanical energy, namely wind.
It may seem a bit strange to view the weather system as a kind of machine and compare it with engineered constructs like an automobile engine, but it is sound physics because all such systems are bound by the same fundamental physical laws and they utilizes the same basic phenomena to create movement from heat.
A heat engine cannot convert heat directly to mechanical energy since that would break the second law of thermodynamics. What are needed are temperature differences. The greater temperature difference the greater effect of the machine. The amount of the energy in the temperature difference that is converted to mechanical energy is called the machines efficiency.
And here we have a very interesting, but less known fact of heat engines; the maximum theoretical efficiency decreases with increasing temperatures. This is interesting because it negates the conventional wisdom and often cited myth that a warmer climate leads to
more storminess, like the claim in the Guardian “a warmer planet has more energy to power stronger storms”, see http://www.theguardian.com/environment/2011/jun/27/climate-change-extreme-weather-2010.
Let us therefore take a look at the theoretical foundation of this effect. This is described by Carnot’s theorem.
Carnot’s Theorem says that the maximum efficiency drawn from a heat engine is the temperature difference between the warmest element and the coldest element divided by the temperature of the highest element.
Expressed as a formula it says: Emax = (Th-Tc)/Th.
Emax is the maximum efficiency
Th is the high temperature element measured in Kelvin
Tc is the cold temperature element measured in Kelvin.
The Carnot cycle is an ideal reversible cyclic process involving the expansion and compression of an ideal gas, which enables us to evaluate the efficiency of an engine utilizing this cycle.
For an interactive demonstration of the Carnot heat engine cycle, courtesy of the University of Virginia, click on the image:
Three important effects can be seen from Carnot’s theorem. The first is that a temperature difference is a necessary condition for converting heat energy to mechanical energy such as wind.
The second effect is that even if we had a perfect heat engine with zero internal friction; it would not achieve anything close to 100% efficiency. The maximum theoretical efficiency for a heat engine operating between 300 K and 600K is for example 50%. The efficiency of a real machine would of cause be considerably lower.
This is why our car engines only operate at about 25% efficiency. The warm element for a car engine is the exploding fuel inside the cylinders and the cold element is the air intake.
The best coal fired power plants have about 40% efficiency and the best gas powered about 55%. The cold elements for those plants are the coolant water, and those with highest efficiency utilize cold seawater as coolant.
Warming gives less efficiency
The third effect is as mentioned above, that, for a given temperature difference between the warm element and the cold element, the efficiency will decrease if both elements heat equally much. On cold days one can see a discernible effect of this in car engines; because the air intake is colder, the engine gives somewhat more power and higher efficiency.
This is also why some turbo charged engines have intercoolers. The turbo gives higher effect, but a non-intentional side effect is that it also increases the temperature in the air intake which will reduce the efficiency. The intercooler reduces the temperature increase introduced by the turbo.
The same effect applies to the wind formations in the atmosphere. Consider the summer temperature in the northern hemisphere; the cold element is the Arctic with a temperature of approximately 0 Celsius and the warm element is in the tropics with approximately 35 Celsius.
The Carnot theorem gives a maximum efficiency in this temperature range of 11.36%. If the temperature increased with 1 Celsius all over the globe, i.e. the difference changed to 1 Celsius in the Arctic and 36 Celsius in the tropic, the maximum efficiency would sink to 11.32%.
This is a minuscule difference, but the point is that it is a decrease, not an increase as the conventional wisdom will have it.
Less temperature differences on the surface
In addition to the effect of higher overall temperatures, the temperature differences will also be smaller. It is quite uncontroversial that the largest effect of global warming is on the cold polar winters and the smallest on the hot tropical summers.
![GFDL_CM2p1_SfcTemp_JJA_DJF_A1B_wht3200x2000[1]](http://wattsupwiththat.files.wordpress.com/2013/12/gfdl_cm2p1_sfctemp_jja_djf_a1b_wht3200x20001.png?quality=75)
However, to be fair, this is not all there is to this. Some climate models tell that the temperature differences in the upper troposphere will increase and this may have larger effect than both the reduced differences on the surface and the higher temperatures.
No settled science there.
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Larry Ledwick says:
December 28, 2013 at 9:39 am
I agree that the water cycle has an effect but the fact remains that descending air warms at the dry lapse rate.
I think that the latent heat released on condensation mostly if not all gets radiated out to space from the condensate rather than moved to a new location.
I see the water cycle as a lubricant for the process which means that circulation changes can be less violent than would otherwise be necessary when internal system forcing elements arise such as changes in the proportion of GHGs.
phlogiston says:
December 28, 2013 at 12:07 pm
I was commenting on another poster’s ‘design’ and assumed the pressure injected at the high level would be enough to provide enough remaining inflation to give heat information at the surface.
However one designs the experiment it is correct that descending dry air warms at the dry lapse rate whilst the initial parcel would have cooled at the lesser moist rate.
TB says:
December 28, 2013 at 1:17 pm
The details that you refer to don’t matter in the scheme of things because at any given moment 50% of the atmosphere is rising and 50% is descending.
What goes up must come down.
It doesn’t deny the greenhouse effect, it IS the greenhouse effect.
The GHE is the consequence of mechanical processes and not radiative processes.
TB said:
“This is (relatively) large mass air movement that has mechanical means and constraining temp profile to cause it. Those means are not available in the wider atmosphere, at least when not equally balanced by air returning upward again to redress the balance.”
Why are those means not available in the wider atmosphere?
All air ascending anywhere is matched by air descending somewhere else.
The constraining temperature profile is provided by the gravity induced lapse rate which underpins the actual observed lapse rates which vary according to atmospheric composition in different layers
However in the end the sum of all observed lapse rates must net out to the gravity induced lapse rate if the atmosphere is to be retained.
That is why the Earth’s lapse rate is like a sideways ‘W’ due to composition variations as one goes up. That ‘W’ shape is a consequence of the circulatory contortions necessary to net out to the ‘ideal’ gravity induced lapse rate.
This heat engine model does make me wonder about the weather 15,000 years ago. Were the storms stronger then? Were the tropics colder? Were there three Hadley cells in the Northern Hemisphere, or only one? If only one, there would be quite a collision of warm and cold air masses. I have no way to evaluate it, but perhaps such a change could drive ice formation over the northern continents.
As a crude idea, let’s say a very strong cold air mass diving west from North America toward the equator could drive a mass of warm moist air into the North Pacific. The angular momentum of the equatorial air would drive it eastward over the continent, where the moisture would be deposited as snow. Perhaps a similar flow of cold air from Europe drove moist air from the Atlantic back north and over the continent.
I am just wondering if a radical change or complete breakdown of the Hadley cell structure in the north might be a feature of ice ages, and how that hypothesis might be tested. Perhaps the Younger Dryas was a temporary return of the ice age air flow. Are there any obvious triggers for such a change?
Using our heat engine model, it seems a possible explanation is the temperature difference between an icy mid-continent and equator would be much greater and the northern tropical Hadley cell energy would increase, while the others would decrease. Consequently, it seems to me the tropical cell would grow to cover a greater span of latitudes. Even if the three-cell structure remained, the northern polar and subtropical cells would be anemic compared to a very energetic north tropical cell.
Does this scenario make any sense at all?
Holy crap! I checked Google…
http://www.fields.utoronto.ca/programs/scientific/10-11/biomathstat/Langford_W.pdf
Not sure they have the right conclusions, but the idea of a single Hadley cell is supported. Unfortunately, it seems they think a reduced temperature difference between the equator and poles drives it. Well, if the cold goes farther south, then perhaps the conditions are met just the same.
” Hoser says:
December 28, 2013 at 1:33 pm ”
A single Hadley cell is very much a reality if snow and ice reach 35-40 degrees latitude.. If the pressure becomes so great at the poles that a cell is crushed into oblivion it might take thousands of years to regain it or it might never come back. The big question is what drives the change… I think its the sun despite what some around here think. We are missing a link to our sun or we are simply ignoring one that does not seem relevant right now.
Thanks to Willis Eschenbach and Jan Kjetil Andersen, especially, for bring us such an interesting investigation into the Earth as a heat engine and for insights into the efficiency and effects of all heat engines. Top rate stuff here!
Stephen Wilde says:
December 28, 2013 at 1:24 pm
TB says:
December 28, 2013 at 1:17 pm
The details that you refer to don’t matter in the scheme of things because at any given moment 50% of the atmosphere is rising and 50% is descending.
What goes up must come down.
It doesn’t deny the greenhouse effect, it IS the greenhouse effect.
The GHE is the consequence of mechanical processes and not radiative processes.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
“What goes up must come down.”
Correct – which is why your hypothesis wont work.
And No, I disagree – the GHE is a consequence of radiative effects.
When watching weather patterns I’ve always been struck by the sheer size and power of winter storm systems. Comparing the cold weather low systems against the so called cyclonic warm water storms, there isn’t really a comparison. The warm water systems are small, contained storms that can only ramp up power over clear seas without storm destroying upper winds or dry air sneaking in.
The Carnot engine concept goes a long way towards describing these systems on a macro scale. Right up to Polar storms with hurricane force winds over land or ice.
There are many naysayers above but none have yet to offer a correction, just negatives.
What are they ‘spraying’ in the skies!!!!???
What is really in those contrails!!!???
Is it really a hazard to humans to be breathing these materials!!???
And HAARP!!! More atmosphereic experiments!!???
BTW, Anthony and mods, the video left by michaelwiseguy in the comment above:
. . . http://wattsupwiththat.com/2013/12/28/climate-as-a-heat-engine/#comment-1515681
contains ALL THAT plus more … here is the same vid again:
PS Can’t you just boot this guy once and for all?
PPS No one will notice he is gone …
[fixed thanks -mod]
.
It seems everyone want to go back to GHG’s rather than look at the functions of the heat transfer due to temperature imbalance/air mass movement. The more I look at this comparison to a Carnot Engine the GHG has little or no effect on the system when looked at from this point of view.
Given the recent studies and papers out showing that GHG’s have been massively overstated in their cumulative effects I’m inclined to look more closely at this point of view.
Oops
Anthony and mods – the vid I was referring to:
The wind then performs ‘work’ moving waves, trees, ice, dust etc.
Jan
I think the problem here is not with most of what you say but rather the approach; the same approach taken by climate modellers. Your approach assumes that reductionism works for something as complex as the climate. Yes, they may rely on fundamental principles and can be built up from these elementary components, but it all falls apart firstly because of imperfect implementations, and secondly, limited computational power. It’s a fool’s errand.
On a general point, what is wrong with accepting we’re crap at modelling nature. It’d save us a lot of money: USGS, MetOffice, EPA…etc.
> Stephen Wilde says:
December 28, 2013 at 1:32 pm
TB said:
“This is (relatively) large mass air movement that has mechanical means and constraining temp profile to cause it. Those means are not available in the wider atmosphere, at least when not equally balanced by air returning upward again to redress the balance.”
Why are those means not available in the wider atmosphere?”
Because there are a limited number of mountains on the Earth’s surface. For a start ~70% of it is ocean.
“All air ascending anywhere is matched by air descending somewhere else.”
Correct?
“The constraining temperature profile is provided by the gravity induced lapse rate which underpins the actual observed lapse rates which vary according to atmospheric composition in different layers”
?? You’ll have to pass that by me again, I’m sorry.
“However in the end the sum of all observed lapse rates must net out to the gravity induced lapse rate if the atmosphere is to be retained.”
No, there is another influence you overlook and that is buoyancy. Gravity will induce a LR, yes, however there is another LR that modifies that and that is the natural LR induced by ascending/descending air. Where the loss/gain of internal energy of an air parcel allows the temp of that parcel to alter at a specific adiabatic rate. I maintain that this is not the same as a gravity induced LR.
“That is why the Earth’s lapse rate is like a sideways ‘W’ due to composition variations as one goes up. That ‘W’ shape is a consequence of the circulatory contortions necessary to net out to the ‘ideal’ gravity induced lapse rate.”
No, part is due to gravity + the up/down buoyancy induced lapse, the other is due to composition – ie the Stat absorbs UV and therefor has a rising temp due presence of O3. The Meso is in collision with Solar particles and is even warmer due collision.
The BDC (Brewer Dobson circ) has an influence in it’s formation as well as PV on isentropic surfaces.
But the causation of the Tropopause is complicated…..
http://www.atmosp.physics.utoronto.ca/SPARC/SPARCImplementationPlan/3_Processes.html
While not near so elegantly I recently wrote about how the thermal energy in the oceans was transformed into kinetic energy when thermal differentials created the currents in the seas.
http://carolinacowboy.wordpress.com/2013/12/19/speaking-of-heat/
TB says:
December 28, 2013 at 1:01 pm
“Now we have something called Coriolis force that ensures that air moving over the Earth’s surface carries the momentum of the Earth beneath it. So for air moving north (in a W’ly jet) it will be moving (relatively) E>W at a greater rate than the land surface blow it.”
In the NH the jet is W>E even when moving N or S of course.
The polar jet with the thermal gradient between polar air and sub-tropical air has the biggest difference with the strongest winds. I didn’t mention the sub-tropics jet which is usually the difference in temperature between the tropics and sub-tropics and has a much lower thermal gradient with much weaker winds. The tropics can also have a easterly based jet stream and this is dependent on dry air clashing with high moisture air at higher attitudes only, very little thermal related. The reason why I didn’t like to call the jet stream caused by thermal gradients because it isn’t necessarily so. Although it is highly thermal gradient related and it is strongly a combination of the planets rotation on its axis (Coriolis) and atmospheric heating by solar radiation.
The polar jet can be absent in places when polar air and sub-tropical air fail to meet, so not only a thermal gradient like mentioned before in the tropics. That’s why there can be gaps in jet stream (polar jet) in Winter and especially during Summer.
http://virga.sfsu.edu/archive/jetstream/jetstream_atl/big/1307/13070406_jetstream_atl_anal.gif
Better link for the person before, not just wanting to look at data collection.
http://squall.sfsu.edu/crws/jetstream.html
Steve B says
“No the primary working fluid is the air. The oceans are a moderator not a driver.”
I’m sorry but I disagree. I chose my ‘ammonia refrigerator’ example for a reason. In this refrigerator the energy source is heat from a kerosene flame. There are three molecules trapped in the system – Water, Anhydrous Ammonia, and Hydrogen. The water never boils, and the hydrogen never condenses. Only the ammonia CHANGES PHASE. So the working fluid is ammonia, not water and not hydrogen (although both are needed to make the system work efficiently). It is the ammonia that does the heavy lifting, that stores and then releases the vast majority of the heat transferred in this system.
In our climate system WATER is the working fluid. No other atmospheric gas changes phase and in so doing takes on immense amounts of energy for transport vertically AND laterally. Air cannot even come close to handling the same amount of energy because except for water vapor none of the gases that make up air change phase! The only way they can store and transport energy is through their heat capacity. Even the molar heat capacities of water are greater than those of air:
Air (room temp. and press.) 29.9 (J/mol·K)
Water 74.5 (J/mol·K)
But the energy that is transferred to water during phase change and that is subsequently transported by wind is typically reported in kilo Joules/mole – thats thousands of joules! So the value of the latent heat of vaporization and latent heat of fusion are:
Water 40,680 (J/mol)
Ice 6,000 (J/mol)
Since neither CO2 nor N2 nor O2 ever change phase they don’t participate in this massive heat transfer process. Sure they carry the water and participate in the expansion and contraction of the gases as they rise and fall, but they only carry a very small amount of the energy that water does.
No, I’m sorry but I disagree with you, Steve B. Water is definately the working fluid in our climate system. But I do agree with your statement that water is a “moderator”. Without water as the working fluid “moderating” (or in Willis’ words “governing”) the climate system our planet would be a much more extreme place to live in.
re charles nelson says:
December 28, 2013 at 2:46 pm
“The wind then performs ‘work’ moving waves, trees, ice, dust etc.”
Whilst the movement of waves, trees, dust and the like provides a visual impression of “work” being done, what is not so evident is the transfer of heat and moisture between the air and the surfaces it comes into contact with that is the real “work”.
chris y says: “The cyclone wind speed v can be estimated with this model and other assumptions, giving
v = sqrt((Ts – To)E/To)
where Ts=300K, To=200K and E is a variable related to coupling efficiency of energy between the ocean surface and the atmosphere.”
There’s the problem with your analysis. E, the coupling efficiency, is a temperature-related variable, and could reduce the velocity or even send it the other direction.
Many commenters are missing (perhaps deliberately) the point that to the extent that the atmosphere doesn’t resemble the Carnot cycle, it will have correspondingly lower efficiency. The Carnot cycle gives a measure of the highest achievable conversion of temperature differentials to mechanical energy, e.g., wind. Non-Carnot cycles will perform at a much lower level. Lower efficiency = lower conversion to energy = lower energy storms.
Marc77 says:
December 28, 2013 at 8:53 am
“The upper atmosphere might be cold, but it cannot be used to drive a convection cell”
————————————————————————
Marc,
No, it is energy loss to space from radiative gases that allow buoyancy loss and subsidence in air masses driving convective circulation in the Hadley, Ferrel and Polar tropospheric convection cells.
Without radiative gases, tropospheric convective circulation in our atmosphere would stall and the atmosphere would trend isothermal through gas conduction. Such an atmosphere would be far hotter than our current atmosphere, as it’s temperature would be driven by surface Tmax.
Climate pseudo scientists have relied for years on the confusion most people encounter though the difference between adiabatic heating and cooling of air masses undergoing vertical circulation, and diabatic processes such as energy gained through surface conduction, release of latent heat and intercepted LWIR and energy lost via LWIR to space.
It is diabatic processes that drive buoyancy changes. It is diabatic processes that drive convective circulation.
When radiative and non-radiative energy transports in our atmosphere are solved for simultaneously it is clear that the NET effect of radiative gases in our atmosphere is atmospheric cooling at all concentrations above 0.0ppm.
Matt G says:
December 28, 2013 at 3:03 pm
TB says:
December 28, 2013 at 1:01 pm
“Now we have something called Coriolis force that ensures that air moving over the Earth’s surface carries the momentum of the Earth beneath it. So for air moving north (in a W’ly jet) it will be moving (relatively) E>W at a greater rate than the land surface blow it.”
In the NH the jet is W>E even when moving N or S of course.
No, not always, in jet disruption processes the jet can move E>W under a warm High in an Omega-block as deep cold air is advected west beneath. This is a common cause of the UK’s coldest winter events.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
The polar jet with the thermal gradient between polar air and sub-tropical air has the biggest difference with the strongest winds.
Not necessarily, polar air converging with air in the mid-latitudes is the most common jet-formation, however sub-tropical air on occasion is advected north to further accentuate the thermal gradient. Behind an amplifying Rossby wave FI as it moves along the N’ward cycle, but also on the bottom of the S’ward cycle.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
I didn’t mention the sub-tropics jet which is usually the difference in temperature between the tropics and sub-tropics and has a much lower thermal gradient with much weaker winds. The tropics can also have a easterly based jet stream and this is dependent on dry air clashing with high moisture air at higher attitudes only, very little thermal related. The reason why I didn’t like to call the jet stream caused by thermal gradients because it isn’t necessarily so. Although it is highly thermal gradient related and it is strongly a combination of the planets rotation on its axis (Coriolis) and atmospheric heating by solar radiation.
Correct.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
The polar jet can be absent in places when polar air and sub-tropical air fail to meet, so not only a thermal gradient like mentioned before in the tropics. That’s why there can be gaps in jet stream (polar jet) in Winter and especially during Summer.
Well yes, there needs to convergence of air-masses to cause a tight thermal gradient (jet-stream).
You don’t need subtropical air necessarily – if the polar air is intensely cold ~510/492dm thick (1000-500mb) then in contrast to mid-latitude air of 540/546dm air there is enough contrast (given convergence) to create a strong jet.
NZ Willy says:
December 28, 2013 at 10:14 am
“Don’t overlook the Coriolis force as a primary driver of large-scale wind.”
—————————————————————————————–
I have noted a number of folk making this mistake recently.
Coriolis forces are not a driver of atmospheric circulation. Coriolis forces have no influence on air masses at rest within a rotating reference frame. Air masses must be put in motion before Coriolis forces affect their movement.
It is radiative and non-radiative heating of air masses at low altitude and radiative cooling of air masses at high altitude that drive atmospheric circulation. Coriolis forces then influence the pattern.
One of the most notable effects of rotational forces is the division of tropospheric convective circulation into three main cells north and south of the equator. If the planet rotated slower there would only be two giant Hadley cells.
http://ddata.over-blog.com/xxxyyy/2/32/25/79/Leroux-Global-and-Planetary-Change-1993.pdf
1993… and at least the description of circulation was correct.