Colder with increasing altitude.

[chingel]

I have read some threads on this topic, but I am still confused. Why does temperature drop as you go up a mountain? I have read that since pressure depends on the weight of the air on top of you and as you increase your altitude the amount of air over you decreases, therefore pressure decreases, gas expands and expansion makes its temperature drop. The rising hotter air gets continually cooled due to expansion (or would it start rising at all?). Gas loses internal energy when it has to expand against a force, i.e. do work. But isn't exactly the same amount of work the gas does received as internal energy of the lump of gas next to it that the work is being done upon?

 

[Pkruse]

Air can only be warmed in two ways. The ground can conduct heat to it, or it can absorb light energy passing they it. Clean air and thin air absorb less heat than thick dirty air near the ground, and of course air at altitude can't get as much heat as air near the ground. Everything works to make air at altitude cooler.

 

[Pkruse]

Also, clouds are a radiation heat shield to keep more heat on the ground. So above the clouds the air is also losing heat to the cold of space much more quickly.

 

[HallsofIvy]

I have read some threads on this topic, but I am still confused. Why does temperature drop as you go up a mountain? I have read that since pressure depends on the weight of the air on top of you and as you increase your altitude the amount of air over you decreases, therefore pressure decreases, gas expands and expansion makes its temperature drop. The rising hotter air gets continually cooled due to expansion (or would it start rising at all?). Gas loses internal energy when it has to expand against a force, i.e. do work. But isn't exactly the same amount of work the gas does received as internal energy of the lump of gas next to it that the work is being done upon?

In addition to what pkruse said, gas expands as it contracts (and so gets colder) becauser the gravitational force on it decreases. There is no "work being done" on the "lump" of gas next to it.

 

[chingel]

In addition to what pkruse said, gas expands as it contracts (and so gets colder) becauser the gravitational force on it decreases. There is no "work being done" on the "lump" of gas next to it.

Could you elaborate on that? How does it get colder due to the decreasing gravitational force while expanding as it contracts? I don't understand that statement. Is it just that the molecules convert kinetic energy to potential energy while rising?

I thought the heat energy absorbed and radiated is negligible compared to the heat from the ground. Is the radiation of heat from the air above the clouds big enough to explain a significant portion of the temperature difference? Why wouldn't the hot air rise and warm the upper layers?

 

[Borek]

Why wouldn't the hot air rise and warm the upper layers?

This part I can easily answer. It would expand and cool down on rising, so it will be not able to warm up the upper layers.

 

[sankalpmittal]

Could you elaborate on that? How does it get colder due to the decreasing gravitational force while expanding as it contracts? I don't understand that statement. Is it just that the molecules convert kinetic energy to potential energy while rising?

I thought the heat energy absorbed and radiated is negligible compared to the heat from the ground. Is the radiation of heat from the air above the clouds big enough to explain a significant portion of the temperature difference? Why wouldn't the hot air rise and warm the upper layers?

I knew many people give the reason that air pressure decreases , and so it becomes less dense at higher altitudes and so its less heated. So its colder at higher altitudes.

When you go to a hill station , you feel a lot colder than plains. But do you feel problem in breathing ? No , because air density difference is negligible. Also you go to a hill station which is not at much higher altitude.

The reason is that sun radiates heat energy in shorter wavelength. It does not heat air through which it passes. Hence it heats the plains. Land re-radiates heat at longer wavelength which heats air and each consecutive lump of air gets heated till most of heat is dissipated as it reaches at lumps of air at hill station. Moreover one can include many other points of Pkruse. Hill station gets heated directly but is heated less much as you can see the case here. Same was the point of HallsofIvy though precise.

Further reading : http://www.usatoday.com/weather/resources/askjack/2004-06-23-cold-upper-atmosphere_x.htm

 

[Borek]

When you go to a hill station , you feel a lot colder than plains. But do you feel problem in breathing ? No , because air density difference is negligible.

To some extent it depends on what you mean by a "hill station", but in general you are wrong. When you go up it is not only becoming colder, but also the pressure and the gas density go down. At around 2000 m pressure is already at 80% of the sea level and if you are not well trained you will already feel the difference in breathing during physical activity. Because of the low partial pressure of oxygen you may also get altitude sickness, especially over 2500 meters.

 

[chingel]

This part I can easily answer. It would expand and cool down on rising, so it will be not able to warm up the upper layers.

But wouldn't the energy lost as it expands and loses temperature have go into the air around it, nevertheless increasing its temperature?

Gas loses heat when it does work, gains heat when work is done on it. Some gas expands and does work, other parts get work done on them. At least in my understanding, I didn't understand why the beforehand poster said no work is done on the lump of air.

 

[daveb]

These seem rather poor and incomplete explanations since by the logic of most of these answers the air should always get colder as altitude increases. But at the stratosphere, the temperature increases as altitude increases due to the presence of ozone which absorbs UV light. Then in the mesosphere temperature again decreases with increasing altitude again, and then increases again in the thermosphere (due to low density of air). Wikipedia has a pretty good explanation. Though pkruse has the right idea when talking only about the troposphere.

 

[sankalpmittal]

These seem rather poor and incomplete explanations since by the logic of most of these answers the air should always get colder as altitude increases. But at the stratosphere, the temperature increases as altitude increases due to the presence of ozone which absorbs UV light. Then in the mesosphere temperature again decreases with increasing altitude again, and then increases again in the thermosphere (due to low density of air). Wikipedia has a pretty good explanation. Though pkruse has the right idea when talking only about the troposphere.

This might confuse the OP further though. He meant to ask "why colder with increasing altitude ?" His question can be phrased as - "Why its colder at mountains ?" or "Why its colder at higher elevations like hill stations ?"

The stratosphere lies between 10,000 m to 50,000 m. Jet planes fly so high. So his question remains limited to troposphere only.

In general , though you are cent percent correct.

To some extent it depends on what you mean by a "hill station", but in general you are wrong. When you go up it is not only becoming colder, but also the pressure and the gas density go down. At around 2000 m pressure is already at 80% of the sea level and if you are not well trained you will already feel the difference in breathing during physical activity. Because of the low partial pressure of oxygen you may also get altitude sickness, especially over 2500 meters.

Why ? I have gone to this hill station : http://www.mapsofindia.com/nainital/nainital-tourism.html

It was approximately 1939 m high. It was rather cold there compared to plains. But I did not feel any problem in breathing there. Also , I am just in high school and not in army so I am not trained at all.

 

[Borek]

It was approximately 1939 m high. It was rather cold there compared to plains. But I did not feel any problem in breathing there. Also , I am just in high school and not in army so I am not trained at all.

You are doing a classical mistake of taking your own partial experience and assuming that's how it works in general. It is called anecdotal evidence and carries no weight in general.

Just because you had no problem breathing doesn't mean your endurance was not compromised.

To know how it is you should take a group of people, put them to some kind of endurance/fitness test at sea level and at 2000 m, then judge the situation based on the test results. And such a research has been done many times in the past, performance goes down with the height/lower air pressure.

 

[chingel]

Yeah I mean why does the temperature decrease in the stratosphere. So I understand that the major heat source is the Earth and further up you are further away from the heat source. But still, why doesn't the air rise and warm the somewhat upper layers? Uneven heating of the ground can cause strong winds on the ground, why not between the hotter and colder layers of the stratosphere? If the air cools as it rises, it cools because it is giving heat to other air around it and then why couldn't we have such a circulation, air moving up, giving the heat away and going back down?

 

[DaveC426913]

If the air cools as it rises, it cools because it is giving heat to other air around it

No, it does not cool by conduction, which is what you're describing. It cools because, the same amount of thermal energy is distributed throughout a larger volume. This is called adiabatic cooling.

If you put a gallon of air in an insulated container that had a piston, then operated the piston to increase the volume to 2 gallons, the air's temperature would drop. This is Charles' Gas Law.

V₁ / T₁ = V₂ / T₂

So, if V₁ doubles to V₂ then T₁ will be halved to T₂

 

[Borek]

If the air cools as it rises, it cools because it is giving heat to other air around i

No, it cools down because to expand it has to do work.

 

[chingel]

But if on the other side of the piston you also had air whose volume would decrease by the same amount, wouldn't the energy lost one one side of the piston be transferred to the other side? And isn't it the same way in the case of expanding air, air does work on other air?

 

[DaveC426913]

But if on the other side of the piston you also had air whose volume would decrease by the same amount, wouldn't the energy lost one one side of the piston

The energy is not lost, the 2 gallon volume of air contains the same amount of thermal energy, it is simply distributed throughout a larger volume.

There are lots of way you can complicate the system, true, but the simpler you make it, the easier it is to see the fundamental principles without obfuscation.

 

[chingel]

How is the energy not lost if the temperature drops? Isn't temperature average kinetic energy per molecule, and the number of molecules surely stays the same.

 

[sankalpmittal]

How is the energy not lost if the temperature drops? Isn't temperature average kinetic energy per molecule, and the number of molecules surely stays the same.

Energy is not lost. Its conserved. Though you can say that when temperature of a body drops , its total internal energy in transit , which it possesses , is reduced. But total energy in an isolated system is again conserved.

 

[haruspex]

If a parcel of air expands a little, for whatever reason, it expands the total volume of the atmosphere that much. This means the average height of the molecules in it has increased. So work is done adding to the potential energy. This is quite different from a closed box, and the reason it does not warm another parcel of air.

I think a lot of the confusion over this topic arises because people think of this process as causing the air to be colder higher up. If you could stop the convection, by inserting baffles all the way up, the temperature gradient would be far steeper. The tendency of air to cool when lofted to a lower pressure altitude inhibits such movements, and they only occur when the temperature gradient is steep enough to overcome it. So the expansion doesn't cause it to be colder higher up, it just limits convection's ability to prevent its being so.
At the tropopause, the gradient is no longer steep enough and convection largely ceases.

 

[jartsa]

A cube shaped block of air whose volume is one cubic kilometers expands with force 100 Giga Newtons. That is the force of air pressure on one side of the cube.

If the volume increases 20 %, the energy of expansion will be 200 meters * 100 Giga Newtons = 20 Tera Joules.

That's 20 Kilo Joules per one cubic meter, which has mass of about 1 kg, which cools about 20 degrees when 20 Kilo Joules of energy leaves it.

Now we want to know where the energy goes. Well it goes everywhere at speed of sound. Because the expansion causes a slight air pressure increase everywhere.

 

[haruspex]

the expansion causes a slight air pressure increase everywhere.

No. The atmosphere is not a closed container.
Average air pressure at Earth's surface must be total weight of atmosphere divided by area. Increasing the volume of some of the air does not increase its total mass. If anything, it will decrease total weight slightly because the average height of the air molecules increases.
The energy goes into the atmosphere's gravitational potential energy.

 

[jartsa]

No. The atmosphere is not a closed container.
Average air pressure at Earth's surface must be total weight of atmosphere divided by area. Increasing the volume of some of the air does not increase its total mass. If anything, it will decrease total weight slightly because the average height of the air molecules increases.
The energy goes into the atmosphere's gravitational potential energy.

Sounds reasonable.

But the energy to lift the atmosphere travels around the atmosphere as pressure wave and at speed of sound.

 

[chingel]

No. The atmosphere is not a closed container.
Average air pressure at Earth's surface must be total weight of atmosphere divided by area. Increasing the volume of some of the air does not increase its total mass. If anything, it will decrease total weight slightly because the average height of the air molecules increases.
The energy goes into the atmosphere's gravitational potential energy.

As some amount of air rises and expands, other air must take its place. Wouldn't the overall potential energy of the atmosphere stay the same because the average height of the air molecules stays the same, they just swap places?

 

[SHISHKABOB]

No, it does not cool by conduction, which is what you're describing. It cools because, the same amount of thermal energy is distributed throughout a larger volume. This is called adiabatic cooling.

If you put a gallon of air in an insulated container that had a piston, then operated the piston to increase the volume to 2 gallons, the air's temperature would drop. This is Charles' Gas Law.

V₁ / T₁ = V₂ / T₂

So, if V₁ doubles to V₂ then T₁ will be halved to T₂

Dave, if

\frac{V_{1}}{T_{1}}=\frac{V_{2}}{T_{2}}

and V₂ = 2V₁

then

\frac{V_{1}}{T_{1}}=\frac{2V_{1}}{T_{2}}

∴ T₂ = 2T₁

from which we end up with Charles's Gas Law, which states that, at constant pressure, the volume of an ideal gas is directly proportional to its temperature.

http://en.wikipedia.org/wiki/Charles's_law

 

[haruspex]

As some amount of air rises and expands, other air must take its place. Wouldn't the overall potential energy of the atmosphere stay the same because the average height of the air molecules stays the same, they just swap places?

Of course, but I was just looking at the immediate consequence of a parcel of air expanding in situ, e.g. by being warmed. The question was, where has the energy gone? The suggestion had been that it had gone into compressing the air around it. Readjustment by convection comes later.

 

[haruspex]

Dave, if

\frac{V_{1}}{T_{1}}=\frac{V_{2}}{T_{2}}

and V₂ = 2V₁

then

\frac{V_{1}}{T_{1}}=\frac{2V_{1}}{T_{2}}

∴ T₂ = 2T₁

from which we end up with Charles's Gas Law, which states that, at constant pressure, the volume of an ideal gas is directly proportional to its temperature.

http://en.wikipedia.org/wiki/Charles's_law

Well spotted. DaveC's description clearly does not meet the constant pressure requirement of Charles' Law. To meet that, heat would need to be added to maintain the pressure, and at a doubled volume the temperature would also double.

 

[chingel]

Of course, but I was just looking at the immediate consequence of a parcel of air expanding in situ, e.g. by being warmed. The question was, where has the energy gone? The suggestion had been that it had gone into compressing the air around it. Readjustment by convection comes later.

OK, but once the air is already warmed, what stops it from rising and warming the upper layers. If it rises and cools, mustn't the energy go to the other air around it and if it does, doesn't it succed in warming the upper layers (ie give off its energy at a higher altitude as heat to the air around it)? Why aren't the upper layers then warmed by rising hot air?

 

[haruspex]

OK, but once the air is already warmed, what stops it from rising and warming the upper layers. If it rises and cools, mustn't the energy go to the other air around it and if it does, doesn't it succed in warming the upper layers (ie give off its energy at a higher altitude as heat to the air around it)? Why aren't the upper layers then warmed by rising hot air?

Having expanded due to being heated, it rises (convection) because it is less dense than the air around it. As it rises, it encounters a slightly lower pressure, so expands a little more. This further expansion does more work in the same way as before, cooling the air adiabatically. There will also be some mixing, but in a large parcel of air that's a second order effect.
This rising-expanding-getting dense cycle has diminishing returns, so settles out when the air is at the same temperature as surrounding air. (This is for dry air - moist air is more complicated.)
At the same time, some air must descend to occupy the space vacated. That air gets compressed adiabatically, warming.
Looking at the total picture, the air as a whole is a little warmer than before (we added heat to kick this off), so is a little less dense, so the atmosphere extends a little further into space and has acquired a little extra potential energy. Thus the heat energy lost by the ascending air has not quite all gone into heating the descending air.

 

[sophiecentaur]

But if on the other side of the piston you also had air whose volume would decrease by the same amount, wouldn't the energy lost one one side of the piston be transferred to the other side? And isn't it the same way in the case of expanding air, air does work on other air?

Yes, but it is Mechanical Energy (Work) that is transferred, not thermal energy. What happens inside the cylinder doesn't depend on what the work happens to act on.

 

[russ_watters]

Dave, if

\frac{V_{1}}{T_{1}}=\frac{V_{2}}{T_{2}}

and V₂ = 2V₁

then

\frac{V_{1}}{T_{1}}=\frac{2V_{1}}{T_{2}}

∴ T₂ = 2T₁

from which we end up with Charles's Gas Law, which states that, at constant pressure, the volume of an ideal gas is directly proportional to its temperature.

http://en.wikipedia.org/wiki/Charles's_law

Adiabatic cooling (aka, adiabatic expansion) does not happen at constant pressure.

What you are describing is what happens at the surface: it is heated and expands at constant pressure. That's what causes it to rise.

 

[russ_watters]

Well spotted. DaveC's description clearly does not meet the constant pressure requirement of Charles' Law. To meet that, heat would need to be added to maintain the pressure, and at a doubled volume the temperature would also double.

Which is why that's not what happens. Again, Dave said adiabatic cooling.

http://apollo.lsc.vsc.edu/classes/met130/notes/chapter6/adiab_cool.html

 

[SHISHKABOB]

Adiabatic cooling does not happen at constant pressure.

well, right, I was just pointing out the error in terminology

I was *only* pointing out that Charle's Gas Law, which Dave mentioned, requires constant pressure. It was offtopic, I guess, technically, because I wasn't trying to add anything to the discussion of why it gets colder with increasing altitude.

 

[russ_watters]

Yes, you're right, sorry. Dave used the right term for what was happening but applied the wrong equation. That's what I get for only reading half a post.

 

[sophiecentaur]

I have read some threads on this topic, but I am still confused. Why does temperature drop as you go up a mountain? I have read that since pressure depends on the weight of the air on top of you and as you increase your altitude the amount of air over you decreases, therefore pressure decreases, gas expands and expansion makes its temperature drop. The rising hotter air gets continually cooled due to expansion (or would it start rising at all?). Gas loses internal energy when it has to expand against a force, i.e. do work. But isn't exactly the same amount of work the gas does received as internal energy of the lump of gas next to it that the work is being done upon?

This thread seems to have lost its way a bit (so what's new?)
I quote the original question and the simplest answer must explain the steady state, static condition, not involving convection / mixing / adiabatic cooling / heating by the ground etc..
Consider a simple column of a gas air, in equilibrium in an insulated cylinder. In an equilibrium situation the air at the bottom of the column will not rise if it is MORE DENSE than the air above it. This can occur even when it is 'warmer', as long as the pressure is greater. So a temperature / pressure profile can occur which will not allow convection but where the temperature at the bottom is higher than the temperature at the top.
The atmospheric pressure is approximately halved for every 5km increase in height (for constant temperature). Applying
P₁V₁/T₁ = P₂V₂/T₂
to this simple model of a column seems to indicate that a mass of air at sea level at a temperature 300K will occupy a smaller volume than the same mass of air at 5km height (half the pressure), if the temperature at 5km is greater than 150K. (Someone else please check this)
This result is extreme and not realistic but it makes the point, I think. There are many other factors at work but it does put to bed the notion that the Hot Air must rise up through the Cold Air.

 

[D H]

Consider a simple column of a gas air, in equilibrium in an insulated cylinder. In an equilibrium situation the air at the bottom of the column will not rise if it is MORE DENSE than the air above it.

The equilibrium condition for your isolated column of air is hydrostatic equilibrium and a uniform temperature throughout. This is the condition that maximizes entropy. There is a non-equilibrium local max in entropy for your isolated column. This local max also is in hydrostatic equilibrium but has temperature falling with increased altitude at the adiabatic lapse rate.

This isolated column is not a good model of the Earth's atmosphere. The Earth's atmosphere is not an isolated system and it is far from thermal equilibrium. The atmosphere is primarily heated from below and radiates into space from above.

The atmosphere is typically closer to that local max (adiabatic lapse rate) than it is to the global max (constant temperature), so the atmosphere is typically driven toward that local max in which temperature decreases with altitude. But not always. Sometimes thermal inversion layers set up in the atmosphere. Rising air stops at the inversion layer -- until it finally punches through. That's when all kinds of havoc such as tornados can result.

 

[SHISHKABOB]

Yes, you're right, sorry. Dave used the right term for what was happening but applied the wrong equation. That's what I get for only reading half a post.

oh it's no problem at all :P I probably should have been a bit more explicit in my post

 

[sophiecentaur]

The equilibrium condition for your isolated column of air is hydrostatic equilibrium and a uniform temperature throughout. This is the condition that maximizes entropy. There is a non-equilibrium local max in entropy for your isolated column. This local max also is in hydrostatic equilibrium but has temperature falling with increased altitude at the adiabatic lapse rate.

This isolated column is not a good model of the Earth's atmosphere. The Earth's atmosphere is not an isolated system and it is far from thermal equilibrium. The atmosphere is primarily heated from below and radiates into space from above.

The atmosphere is typically closer to that local max (adiabatic lapse rate) than it is to the global max (constant temperature), so the atmosphere is typically driven toward that local max in which temperature decreases with altitude. But not always. Sometimes thermal inversion layers set up in the atmosphere. Rising air stops at the inversion layer -- until it finally punches through. That's when all kinds of havoc such as tornados can result.

Why should you say that? My model uses PV/T and thus includes non-uniform temperature. My column would have a temperature gradient maintained to fit and hydrostatic equilibrium is fine under those circs, surely. I don't think that heat flow up or down the column via the gas would be significant or that it would introduce a difference in the result; the temperature gradient would still be there, even with some conductive heat flow. What has entropy to do with this simple model?
My point in suggesting the model was that it would be a good first-step to eliminate all the factors that you say affect a real atmosphere. I didn't claim that it was a good model (I specifiied that the other factors are ignored in it) but the one thing that it does do is to show that hot at the bottom and cold at the top is a sustainable situation. I wouldn't, for a minute, suggest ignoring all your other factors but I think you would agree that, looking at them all at once, as a first step into learning about the Atmosphere, could be a bit daunting. One thing at a time, wherever possible. The OP could probably benefit from a very easy start on the whole business. If I have insulted his intelligence then I apologise to him.

This may be yet another occasion when it would help if the level of the original question could be classified in some way and could help in getting the answering comments pitched appropriately.

 

[D H]

What has entropy to do with this simple model?

It has everything to do with it. An isolated system will move toward a configuration that minimizes energy and maximizes entropy. Your simple model says that temperature should not increase with altitude. The second law of thermodynamics suggests that the atmosphere should seek a uniform temperature state. Your example says likewise. This is, I think, the heart of the OP's confusion.

The way out of this apparent paradox is that the Earth's atmosphere is far from equilibrium conditions. Once you get far enough away from equilibrium, a nearby local min in energy / local max in entropy can dominate over the global min / global max.

 

[sophiecentaur]

OK, I accept that the energy situation would not be thermal equilibrium - any more than a hovering helicopter energy situation would be equilibrium. Nonetheless, a helicopter can hover and my column can sustain that temperature gradient over it with no mass movement of air. That's all I'm saying. Where the energy comes from is another matter but, as you say, it will involve some extra entropy increase somewhere else.
Something that did strike me was that the temperature difference can be much greater than what we find in practice. That, of course, is due to all your other perfectly reasonable arguments.
Shall we say that we could have 'mechanical' equilibrium in my model (which is what I meant).

 

[Bob S]

A good explanation of why air gets colder with increasing altitude is the adiabatic expansion of air as the pressure decreases. See discussion of adiabatic expansion of air, and how it applies to our atmosphere in http://farside.ph.utexas.edu/teaching/sm1/lectures/node56.html, and see equations 329 et seq.

 

[chingel]

That is an interesting idea that the air wouldn't rise at all, because the air higher up, even though it is colder, is even less dense due to the decrease in pressure.

I am still having problems with the other explanation of rising and cooling. Bob S, wouldn't the adiabatic cooling cause adiabatic warming of the air around it? And if it does, does it matter if the warm air rises and stays there or just gives its heat off there and circulates again, wouldn't the effect still be warming the upper layers?

 

[russ_watters]

I am still having problems with the other explanation of rising and cooling. Bob S, wouldn't the adiabatic cooling cause adiabatic warming of the air around it?

Yes! A warm air mass rises and cools while a cool air mass falls arount it and warms.

And if it does, does it matter if the warm air rises and stays there or just gives its heat off there and circulates again, wouldn't the effect still be warming the upper layers?

Yes, there is a net heat transfer out of the atmosphere, but that doesn't imply that the convection cell has to be warmer at the top than at the bottom. It just has to be warmer than space.

 

[chingel]

Doesn't the energy lost by the expansion have to go somewhere? Isn't that place the air around it, not just that cool air falls and warms there, but the expanding air itself warms it? Beforehand gravitational potential energy was talked about. But isn't the gravitational potential energy increased during initial warming of the air, once it starts rising and expanding, as much air as is expanding should contract and fall, leaving the height of the whole atmosphere and its gravitational potential energy the same.

I am getting the impression that it doesn't heat the upper layers, because when it gets there its temperature has decreased, but doesn't that mean the lost thermal energy has gone into the air around it and it already has warmed it?

 

[sophiecentaur]

Work is done in raising the mass of air. That accounts for a lot of the energy transfer.

 

[russ_watters]

Doesn't the energy lost by the expansion have to go somewhere?

The air masses exchange mechanical work when one expands and the other contracts. Consider a double-ended piston with air filled cylinders: heat one side up, then release the piston and the hot side will expand and cool while the cool side contracts and heats.

 

[russ_watters]

Work is done in raising the mass of air. That accounts for a lot of the energy transfer.

This gets complicated by how comprehensive you want the definition of the system to be:

1. If you just focus on the expanding parcel of air, it may look like it is gaining gravitational potential energy...
2. ...but realistically, it is rising because of buoyancy, so the atmoshere is actually losing gravitational potential energy.
3. ...but since this is a convection cycle, it is constantly fed by heat and if it is in a steady-state will result in zero net upwards or downwards movement of air and thus no gravitational potential energy change.
4. ...but the real Earth has day and night (as well as solar activity cycles), so during the day the atmosphere is warmer and expands (locally), increasing its gravitational potential energy while at night it gets cooler and contracts, decreasing its gravitational potential energy.

The way I would analyze this is as shown in my previous post, which corresponds to #2: gravitational potential energy is irrelevant to the main issue of the thread.

 

[stacybyars]

Great question and answers here. I thought this question would be easier to answer but I learned more than I bargained for.

This point fro Pkruse was fascinating: "Also, clouds are a radiation heat shield to keep more heat on the ground. So above the clouds the air is also losing heat to the cold of space much more quickly"

 

[Borek]

This point fro Pkruse was fascinating: "Also, clouds are a radiation heat shield to keep more heat on the ground. So above the clouds the air is also losing heat to the cold of space much more quickly"

I suppose I will be corrected, but I think this statement is misleading.

Air above clouds doesn't lose heat faster - it gets cold faster. That's not the same thing.

Assuming clouds layer works as insulation air above is not heated from the bottom. That means after losing the same amount of heat air above clouds gets colder than the same air losing the same amount of heat but being heated from the bottom.

If the air is isolated from the heating and gets colder faster, speed at which it loses heat goes down much faster than in the case of the air heated from the bottom - after all air loses heat to space only by radiation, and amount of energy emitted is proportional to T⁴. That means in the same amount of time amount of energy lost is smaller, not larger.

 

[stacybyars]

Thank you for clearing this up!