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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[snip – chemtrail garbage – policy violation -mod]
your car has a mass air flow sensor that measures the mass of air flowing through the intake system. with cooler denser air the computer increases the length of time the injectors stay open allowing more fuel to the cylinders. the turbo pushes more air in than atmospheric pressure alone but still benefits from cooling the compressed air to increase density. more air =more fuel=more power
I grew up on the southern edge of the Sahara and one memory I have of my weekly chores was refilling the kerosene tank at the bottom of our refrigerator, and cleaning the long glass mantle of its weekly accumulation of black soot. Later in life I learned that this refrigerator was an absorption unit and that the “working fluids” were anhydrous ammonia, hydrogen gas, and water. The entire working fluid system was sealed and had no moving parts, yet it continuously provided ice in the freezer section and cold air in the refrigerator section off of heat generated by burning a miniscule amount of kerosene (about a quart/day). This type of “engine” achieves its remarkable cooling by both phase change and multiple Carnot cycle expansion/contraction/pressure changes of the working fluids. At the heart of the engine is the “expansion” and boiling of liquid ammonia/hydrogen gas mixture inside the freezer coils that created the chilled freezer surfaces. This gas mixture is condensed and separated by mixing with water. Since ammonia is highly soluble in water but hydrogen is not, the ammonia dissolve (absorbs) into the water but the hydrogen does not and collects above it as purer hydrogen gas. The water/ammonia mixture is then collected at the bottom of the refrigerator and percolation “boiled” using the heat of a kerosene fired flame to boil the ammonia out of the water. The “hot” ammonia gas is cooled at the top of the refrigerator by passing it through a heat exchanger, and the liquid ammonia is mixed with hydrogen gas again, collected and piped back into the freezer compartment where it begins the cycle again. The mixing and “asborption” of this type of “heat engine” is capable of extractng heat from one location (freezer coils) and moving it to another (ammonia condensing heat exchanger) using even greater heat as the energy source that drives all the cycles. My point in telling this story is that, just as Leonard Weinstein has stated, the addition of just a single phase change, where the volume and density of the working fluid changes significantly, signficanty increases the efficiency of the engine. In the case of the climate system the primare working fluid is not the air – rather it is water! The addition of two phase changes (from vapor all the way to solid), describes a thunderstorm and accounts for astoundingly high energy transfer!
Richard Sharpe says:
December 28, 2013 at 9:07 am
Richard
The total amount of energy is not of any use since energy cannot be converted directly to mechanical energy. What matters are the temperature differences, or said in another way, the excess energy in the parts of the atmosphere that are higher than the lowest temperature on the planet.
Since turbulence is also a form of mechanical energy, the turbulence will also be lower. The effect of higher overall temperature is that the warm parts simply warm up the colder parts without creating as much movements in the air as in colder conditions.
Correction:
Automobiles MAY have had better “efficiency” on cold days in the era of carboraters …because the mixture was more proper.. BUT, since your engine coolent is controlled by a thermostat, the “sink” temp for an Otto Cycle, Auto Engine is almost completely constant the year around. (Whereas for a power plant, cooled with river water, for example…when the river goes to 35 F, the sink DOES allow a greated Delta T and the efficiency is up!)
Now, for the reality of the Otto cycle, the ambient temperature ALSO influences the amount of energy needed to go from AMBIENT to the combustion temp. THE GREATER ENERGY USED HEATING THE air up as it comes into the combustion cycle, causes a NET ENERGY LOSS (it takes away from the heat conversion to mechanical. Therefore, Otto cycle engines would tend to LOSE a little efficiency during colder weather.
DON’T LOOK FOR IT, as you are idling, warming up, stoping and starting MORE and your net mileage is going to go down, no matter!
TB says-
“…will make Hurricanes, Typhoons, Cyclones more powerful, as they derive their energy from SST’s, which will be higher in a warmer world.”
Kerry Emanuel of MIT described cyclones using a Carnot cycle model in the August 2006 issue of Physics Today. The SST at 300K is the hot end, the troposphere (15 km) at 200K the cold end. 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 are at least 3 interesting conclusions one can take from this simple model.
1. If the sea surface temperature warms by 1K, then Ts=301K, To=200K, and the wind velocity is predicted to increase by 0.5%. There is no way to discern this tiny change.
2. If the climate models are to be believed, then the tropical troposphere should warm more than the surface. For example, if the sea surface warms 1C, the troposphere hot spot should warm 1.5C. That is, Ts=301K and To=201.5K. Then, the cyclonic wind velocity is predicted to DECREASE by 0.6%. Go figure…
3. Because we know that sea surface temperature changes of 5C (eg from 25 C to 30 C) can have a huge impact on cyclonic wind speeds (provided other conditions like wind shear are also just right), the Carnot model is useless for predicting wind speeds.
So, the Carnot model for cyclones predicts that a warmer world will have stronger cyclones, weaker cyclones or ‘this model is for entertainment purposes only.’
Chris Y says:
“So, the Carnot model for cyclones predicts that a warmer world will have stronger cyclones, weaker cyclones or ‘this model is for entertainment purposes only.’”
Well said. The Carnot model is for a closed system. Any application beyond that is just funnin it.
Jan,
Excellent graphics accompanying clear discussion! Thanks for a useful and interesting primer on heat engine ‘basics’ and how they relate to our planetary weather and climate. Many here will niggle and quibble about various aspects of your treatise but I truly hope they do not lose sight of its usefulness as an education tool for the physics-impaired layman we all know that seek greater understanding of what drives our weather and climates.
Well Done!
MtK
It’s not the cooler air which improves a gas engine’s efficiency, it’s the density. Colder air is more dense, which means it can be mixed with more fuel, increasing the rotational torque generated by the piston’s downward movement. Likewise, turbochargers increase the density of the air in the cylinder, even though they heat the air during compression. This is why an intercooler is used, to reduce the temperature of the pressurized air back down to the ambient intake. Drag and drift guys have been known to even spray Nitrous Oxide over the outside of the intercoolers, because as it evaporates it can carry away dramatic amounts of heat, increasing the intercoolers’ efficiency.
Carbureted engines did not adjust well for air density in colder climates, other than the natural increase in venturi effect efficiency as density improved, so they typically were set to run rich, and just leaned out as the air got colder, increasing power slightly for the air they could ingest. Up to a point, leaning out the air/fuel ratio can increase power slightly, but can increase the chance of “knock” (pre-detonation of the mix in the cylinder before the piston is close to top dead center). Modern fuel injected motors run much leaner right from the start, and the sensors keep the motor on the ragged edge for both fuel efficiency and power. When the air temps go down, power does increase slightly, but within a range of only 3-5%. Hardly enough to be felt by the seat of your pants for most drivers. Modern fuel systems can adjust up to a 7-8% range within their pre-programmed parameters, which generally covers all situations outside of a really bad tank of gas.
If the earth has to be seen as a heat engine then it has to be seen as two heat engines the northern hemisphere heat engine and the southern hemisphere heat engine.The range of seasonal solar forcing change is greater at higher latitudes for each hemisphere than at the equater as the earth tilts toward the sun and away from the sun,this range would not increase or decrease in a uniformly warming world it would just shift upwards (summer and winter).The important question here is if the world is warming or not and if it is then the range will shift upwards in both hemispheres and that is what we should see the atmospheres in both hemispheres should hold more water vapour season by season if the earth is warming.
Word search:
Chaos: 0 / 0
Dissipative: 0 / 0
Nonlinear: 0 / 0
(Far from) equilibrium: 0 / 0
Turbulence: 0 / 0
Null points
I think DonV has an important point: ” In the case of the climate system the primare working fluid is not the air – rather it is water!.” It’s not CO2 it’s the sun and water.
Stephen Wilde on December 28, 2013 at 9:07 am
“If you fill a balloon of air in the upper atmosphere and bring it down to ground level, the air in it will be warmer than the air at ground level”
An air filled balloon in the upper atmosphere, if brought down to ground level would become shrivelled and almost empty of air, the tiny amount of air present at ground atmospheric pressure would quickly equilibrate with the rubber walls of the balloon, destroying any heat information. Suggest revision of experimental design.
🙂
oaaprogrammer says:
December 28, 2013 at 9:02 am
What drives the jet streams? Are there any data collections on the velocity of jet streams over time?
The jet streams are caused by polar air clashing with sub-tropical air, so the bigger difference between the two, the stronger the winds.
http://www.srh.noaa.gov/jetstream/global/images/jetstream3.jpg
There are data collections.
http://squall.sfsu.edu/crws/jetstream.html
As many have pointed out the Temperature Differential is the key component to our storminess and severity of storms. During the last 30 years we have had a basically stable temperature differential as slight warming was occurring in the short term trend. This warming affected the polar regions and REDUCED the temperature differential. The last 17 years with a flat gradient in temperature changes proved out to continually calm (storm intensity) in both our tropical storms and our over land tornadoes as well.
The last three years has created great turbulence in the polar regions as massive amounts of cooling are occurring. The oceanic heat reserve has blunted the last three years even though Antarctica set 200+ low temp records and increased ice mass to +2 standard deviations. Our temperature differential is growing but the ocean heat reserves have blunted the effects. The Arctic usually follows the antarctic by about two years. Given the number of record lows already we are well on our way to ice rebound.
As the ocean buffer equalizes at the new lower temp, watch for the storms to increase in severity world wide. Add to that the ENSO, ADO, PDO, among other oscillations being cold or neutral this process will become quite fast..
Solar input into our system is low. The energy stream introduced into our heat engine has slowed. While this will not generally affect the tropical zones the polar regions are greatly affected causing our global temperature differential to rise. The mechanical (convection) systems which allow the heat to move from the equatorial regions out to the poles will become more streamlined (less chaotic then they are today) as the Ocean temps re-balance to the new lower energy input. When that happens I expect our storm tracks will again return to the mid latitudes and be a little more predictable.
While the thermodynamics of a steam engine are somewhat comparable and the physics applies in most respects its not a good fit in my opinion.
NZ Willy says:
December 28, 2013 at 10:14 am
The so called Coriolis “force” is simply the direction that objects (and air) must follow in moving across the surface of the earth if angular momentum is to be conserved. Thus it would actually require an external force and thus energy to divert objects from following the trajectories across the Earth’s surface that are a manifestation of the Coriolis effect. Would you claim that a figure skater performing a spin requires additional external rotational force when increasing rotational velocity by tucking her extended arms to her torso?
Jan,
Your graph on Hadley cells is rather useful in this debate as the “norm” for polar Jet intrusion is about the 40th parallel During the last three years that intrusion has dropped to the 25th parallel. This is a good indicator of the pressure differential created by the temperature differential in the polar regions.
This compresses those median Hadley cells limiting major hurricane formation to a narrow corridor and allows cold front disruption over land limiting tornado formation while increasing the areas where they can form. This should sound very familiar as this is exactly how the last three years (or better) have played out.
Rather an interesting way to show just how it is temperature differential which is.driving the climatic engine. Just one more cylinder in a very complex climactic engine.
re Jean Parisot says:
December 28, 2013 at 12:05 pm
I think DonV has an important point: ” In the case of the climate system the primare working fluid is not the air – rather it is water!.” It’s not CO2 it’s the sun and water.
I agree, and believe it is point of phase changes of water that ultimately give us the climate we know.
If the climate was determined by the phase changes of CO2 the climate would be very different.
This article could be turned into a hypothesis for an actual study or experiment to support or disprove the theory. I’m sure all the data needed is already out there or could be gathered for free for an experiment. Design it in a repeatable manner and it could provide the basis for some good science over a few years.
Jean Parisot says:
December 28, 2013 at 12:05 pm
I think DonV has an important point: ” In the case of the climate system the primare working fluid is not the air – rather it is water!.” It’s not CO2 it’s the sun and water.
**********************************************************************************************************************
No the primary working fluid is the air. The oceans are a moderator not a driver. For example take the oceans out of the equation. You will find that the poles will be colder and the equator will be hotter. This will give a greater temperature difference and much stronger winds. You can see this at the moment where the South Pole is colder than the North Pole since there is no water anywhere near the SP to moderate the temps there. You will probably find that Central Siberia is colder than the NP for the same reasons.
Matt G says:
December 28, 2013 at 12:30 pm
oaaprogrammer says:
December 28, 2013 at 9:02 am
What drives the jet streams? Are there any data collections on the velocity of jet streams over time?
The jet streams are caused by polar air clashing with sub-tropical air, so the bigger difference between the two, the stronger the winds.
http://www.srh.noaa.gov/jetstream/global/images/jetstream3.jpg
There are data collections.
http://squall.sfsu.edu/crws/jetstream.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Matt:
To be more complete with your explanation.
Jet streams are driven by thermal contrast.
Northern latitudes are cold (NH) and as we come south the Sun’s elevation causes higher temps. There is a point where this temp contrast manifests itself as a maximum. This is the Polar jet-stream.
Cold air is more dense. Therefore as one rises through it, the level at which, say 300mb (~30000ft) is indicated on your barometer/altimeter will come sooner than if you rise upward through a warm air-mass.
Look at a chart showing 300mb contours. They will depict a tight gradient. Where closest together lies the strongest winds (analogous to a surface pressure gradient).
Now to a parcel of air within the warm air (to south of the gradient usually) will have more air above it that a parcel of air to the north in the colder air-mass. Ie it is at a higher pressure. So what does it do? It moves toward low pressure (usually N but always towards cold air). 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. Similarly air moving N>S will be moving slower than the earth’s surface beneath it. In both cases it turns to the right relative to the earth’s surface.
As the SH is a mirror image, air there turns left on moving from warm to cold aloft. These are thermal winds and although moved by pressure differentials they owe their origin to thermal differential of adjoining air masses.
A strong jet will have a large thermal contrast and vice versa.
Klotzbach and Gray link global cooling to increased Atlantic storminess.
http://hurricane.atmos.colostate.edu/Forecasts/2008/dec2008/dec2008.pdf
See diagram on page 35.
Stephen Wilde says:
December 28, 2013 at 9:07 am
“If you fill a balloon of air in the upper atmosphere and bring it down to ground level, the air in it will be warmer than the air at ground level”
Assuming you mean the upper troposphere that would be because the air was originally humid and cooled during uplift at the moist lapse rate.
If you then capture dried out air and bring it down then it warms at the dry lapse rate which is faster and so it ends up warmer than the surface air.
I have argued elsewhere that the mechanical warming on the descent phase of the convective cycle is what warms the surface above the S-B prediction and not DWIR (Downward Infrared Radiation)
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Stephen:
I have a problem with that.
And that is that free air in the Earth’s atmosphere is constrained by buoyancy.
It cannot penetrate too far downwards because of this. Just as trying to hold a hot-air balloon down is fruitless because it wants to go up!
In the case of Foehn winds and their counterparts around the world (Chinook etc). They are constrained by stable air and wave motion over higher ground (capping inversion layer) – having risen on the windward side up an SALR, lost water content, and spilled down the leeward side under descending wave motion along a DALR. Hence the arrival of air at a much higher temp.
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.
And no I do not agree with you hypothesis that it explains the warming at the surface to deny a GHE.
Mike Jonas says:
December 28, 2013 at 1:09 pm
What they fail to realize is that storm increase is due to Polar Jet intrusion, as it is today.. They miss the very basic concept of what is driving the air mass changes. Go figure..