Are there more persistent contrails these days?

Dylmar

New Member
I’ve some questions regarding contrail formation that I'm hoping someone here may have some insight on.

Do you think that there are more persistent contrails these days compared to say 30 years ago? Obviously there are more aircraft in the sky, but is the ratio that leave a lasting trail any higher now? Also, do you think that the global warming trend over the same period, which has likely increased the amount of water vapour in the atmosphere, could be a factor in the persistence of contrails?

Thanks

Dylan
 
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George B

Extinct but not forgotten Staff Member
I’ve some questions regarding contrail formation that I'm hoping someone here may have some insight on.

Do you think that there are more persistent contrails these days compared to say 30 years ago? Obviously there are more flights in the sky, but is the ratio that leave a lasting trail any higher now? Also, do you think that the global warming trend over the same period, which has likely increased the amount of water vapour in the atmosphere, could be a factor in the persistence of contrails?

Thanks

Dylan
You pose some complex questions that seem simple but in my opinion are rather difficult to answer.
 

George B

Extinct but not forgotten Staff Member
Dylmar said:
Do you think that there are more persistent contrails these days compared to say 30 years ago?
The short answer is yes.

Dylmar said:
Obviously there are more flights in the sky, but is the ratio that leave a lasting trail any higher now?
This is a YES, likely because of engines with higher efficiencies.


Dylmar said:
Also, do you think that the global warming trend over the same period, which has likely increased the amount of water vapour in the atmosphere, could be a factor in the
This one is more complex. Yes there is more likely more moisture in the higher Troposphere but it is likely to be warmer via global warming, thus temperature probably trumps moisture. I would say therefore, there could be eventually fewer persistent contrails as a result of warming.
 
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Dylmar

New Member
I appreciate it's a complex question. I've not been able to find any definitive answers in studies regarding contrails or atmospheric conditions. I'm just trying to establish if there is a correlation, and if there is, to what extent it is affecting the persistence of contrails.
 

WeedWhacker

Senior Member
Obviously there are more flights in the sky, but is the ratio that leave a lasting trail any higher now?
Yes to this, and to expand further ( pun intended ;) ) on the topic, it is directly related to the advent of the more fuel efficient High Bypass TurboFan engines that are the "norm" today (compared to the older Low Bypass TurboFans, and the straight TurboJet engines of the past).

"Contrail Science" has a section on this:
http://contrailscience.com/persisting-and-spreading-contrails/

 

George B

Extinct but not forgotten Staff Member
What is your reasoning behind saying Yes George?
http://m.earthobservatory.nasa.gov/IOTD/view.php?id=4435

Read the narrative to this NASA photo.

 

SR1419

Senior Member.
I appreciate it's a complex question. I've not been able to find any definitive answers in studies regarding contrails or atmospheric conditions. I'm just trying to establish if there is a correlation, and if there is, to what extent it is affecting the persistence of contrails.

I think the vast majority of increase in persistent contrails can be explained by the growth in air traffic- air traffic has grown over 50% since 2000 alone much less 30yrs ago:

https://www.metabunk.org/threads/growth-in-world-air-traffic-1970-present.2572/

RPK.JPG
 

George B

Extinct but not forgotten Staff Member
I think the vast majority of increase in persistent contrails can be explained by the growth in air traffic- air traffic has grown over 50% since 2000 alone much less 30yrs ago:

https://www.metabunk.org/threads/growth-in-world-air-traffic-1970-present.2572/

View attachment 6593
While you are quite correct above there is some evidence that climatic variation has significant impact on persistence frequency beyond simply greater frequency of flights:

 

Dylmar

New Member
That's very interesting. I suspected that climate variation and atmospheric changes may have played a part. Good find George. Thanks
 

George B

Extinct but not forgotten Staff Member
That's very interesting. I suspected that climate variation and atmospheric changes may have played a part. Good find George. Thanks
Dylmar, here is a Thread about Global warming and persistent contrails, you might find it interesting . . . https://www.metabunk.org/threads/de...educe-the-number-of-persistent-contrails.930/

 
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Ross Marsden

Senior Member.
Last paragraph of Box 8.1...

Since contrail persistence depends on the RH (and not the moisture content), and since upper tropospheric RH changes little as the climate warms, there should be little change in the occurrence of persistent contrails due to climate change. This is from the 2007 IPCC Assessment report, and I doubt this view has changed in the most recent one.
 

Ross Marsden

Senior Member.
In the latest Assessment Report (#5)... (in the downloadable PDF of Working Group 1's report, linked in the Current Documents) page 207, end of first paragraph of section "2.5.5.3 Satellite":
So, there you go.
 

skephu

Senior Member.
Actually, I don't think that higher-efficiency engines would lead to increased persistent contrail generation. The efficiency of the engine can only influence whether a contrail appears or not. But the persistence of the contrail is solely determined by the relative humidity (wrt ice) of the surrounding air. That does not depend on what type of engine you are using. You can use the most efficient engine in the world, its contrail will still not be persistent if the air is not supersaturated with ice.
Also, if the conditions favor a persistent contrail, it will appear regardless of the engine type used.
So I think that the fraction of contrails that persist should not be higher today than it used to be.
 

WeedWhacker

Senior Member
Also, if the conditions favor a persistent contrail, it will appear regardless of the engine type used.
So I think that the fraction of contrails that persist should not be higher today than it used to be.
Incorrect.

A higher efficiency modern high bypass turbofan produces an exhaust that is generally prone to produce a more persistent contrail, and under a wider range of atmospheric conditions that a low bypass for straight turbojet.

This is a scientific fact, sorry.
 

Mick West

Administrator
Staff member
Actually, I don't think that higher-efficiency engines would lead to increased persistent contrail generation. The efficiency of the engine can only influence whether a contrail appears or not. But the persistence of the contrail is solely determined by the relative humidity (wrt ice) of the surrounding air. That does not depend on what type of engine you are using. You can use the most efficient engine in the world, its contrail will still not be persistent if the air is not supersaturated with ice.
Also, if the conditions favor a persistent contrail, it will appear regardless of the engine type used.
So I think that the fraction of contrails that persist should not be higher today than it used to be.
Not true. A contrail can only persist if it first comes into existence. Since higher contrail factor engine make more contrails, they will also make more persistent contrails.

A higher efficiency modern high bypass turbofan produces an exhaust that is generally prone to produce a more persistent contrail, and under a wider range of atmospheric conditions that a low bypass for straight turbojet.
A higher contrail factor does not make a contrail more likely to persist. It just makes a contrail more likely to form in the first place. This might also make the contrail denser - but ultimately if the air is ice supersaturated, then any contrail is going to persist. The difference happens further up the mixing curve
 

skephu

Senior Member.
Incorrect.

A higher efficiency modern high bypass turbofan produces an exhaust that is generally prone to produce a more persistent contrail, and under a wider range of atmospheric conditions that a low bypass for straight turbojet.

This is a scientific fact, sorry.
Please explain the physics behind that statement.

Not true. A contrail can only persist if it first comes into existence. Since higher contrail factor engine make more contrails, they will also make more persistent contrails.
I don't believe that reasoning is correct. If conditions allow persistence, the air is supersaturated with ice. A contrail will always appear, regardless of the contrail factor.
 

skephu

Senior Member.
Perhaps would be best if you read the scientific paper on it:

Contrail Formation and Propulsion Efficiency
Andrew G. Detwiler; Arthur Jackson



Are you making your claims RE: persistent contrails after reading much inaccurate information online? Because, a simple Google search turns up a LOT of false assertions.
I don't have access to the full paper, but from the abstract it appears that it only talks about the conditions of contrail formation, and does not say anything about persistence.
 

Mick West

Administrator
Staff member
Here's the NASA diagram of the formation of a persistent contrail. I have added another line X-A3


Point B is the state of exhaust of a high bypass engine, it's moist, and hot.

Point X (which I added) is a hotter running engine, lower contrail factor. Same moisture.

Ambient conditions are at point A3. They are suitable for contrail persistence. The cooler exhaust mixes with the ambient air, and eventually arrives at A3. On the way there it passes through the region on the graph that is water supersaturated (the yellow portion of the line after point F), so a cloud forms, and hence a contrail.

The hotter exhaust ends up at exactly the same point, however the mixing curve (X - A3) never passes through the "cloud" region (water supersaturation), and so no cloud forms. Since no clod forms, there is nothing to persist.

Edit: Simplified the diagram a little for clarity. (And corrected the caption for point X :oops: )
 
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skephu

Senior Member.
Here's the NASA diagram of the formation of a persistent contrail. I have added another line X-A3


Point B is the state of exhaust of a high bypass engine, it's moist, and hot.

Point X (which I added) is a hotter running engine, lower contrail factor. Same moisture.

Ambient conditions are at point A3. They are suitable for contrail persistence. The cooler exhaust mixes with the ambient air, and eventually arrives at A3. On the way there it passes through the region on the graph that is water supersaturated (the yellow portion of the line after point F), so a cloud forms, and hence a contrail.

The hotter exhaust ends up at exactly the same point, however the mixing curve (X - A3) never passes through the "cloud" region (water supersaturation), and so no cloud forms. Since no clod forms, there is nothing to persist.
That sounds plausible, but you are assuming that the line should cross the blue area (liquid phase), otherwise, nothing will happen.
But point A3 is above the sublimation curve, so if you come from point X, you go into the hatched area, which means that desublimation (direct transition from vapor to solid, also called deposition) can occur (and because the exhaust contains enough condensation nuclei, it will occur). That's how snow and frost form as well.
 

mrfintoil

Senior Member.
Since the climate is essentially getting more wet due to climate change, I have always wondered if this is influencing contrail formation to some degree? I don't think it's any significant, but interesting to know anyway.
 

Mick West

Administrator
Staff member
That sounds plausible, but you are assuming that the line should cross the blue area (liquid phase), otherwise, nothing will happen.
But point A3 is above the sublimation curve, so if you come from point X, you go into the hatched area, which means that desublimation (direct transition from vapor to solid, also called deposition) can occur (and because the exhaust contains enough condensation nuclei, it will occur). That's how snow and frost form as well.
The condensation nuclei present only work for water. A contrail needs to condense as liquid water and then freeze before ice deposition can occur. If there were ice nuclei in the air, then cirrus clouds would form.
 

skephu

Senior Member.
The condensation nuclei present only work for water. A contrail needs to condense as liquid water and then freeze before ice deposition can occur. If there were ice nuclei in the air, then cirrus clouds would form.
Why do you think soot particles from the exhaust would not work as condensation nuclei for direct vapor-to-ice deposition?
 

Mick West

Administrator
Staff member
Why do you think soot particles from the exhaust would not work as condensation nuclei for direct vapor-to-ice deposition?
http://www.faa.gov/about/office_org...odeling/accri/media/Contrail Microphysics.pdf
 

Mick West

Administrator
Staff member
Clarification to the above: soot particles can work as ice nuclei, they just don't work very well. If a plane were flying along magically spraying out nothing but soot, then it's not going to form a contrail. The soot might later contribute to the formation of cirrus (soot cirrus) - although it's not really clear if that happens, or how much.
 

skephu

Senior Member.
http://www.faa.gov/about/office_org/headquarters_offices/apl/research/science_integrated_modeling/accri/media/Contrail Microphysics.pdf
OK. Thank you. I stand corrected.
 

jpsitig

New Member
YES there are. But they are CHEMTRAILS. NOT contrails. Contrails dissipate after a few minutes- not linger for hours at a time- which is a chemtrail.
 
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