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/

Are spreading contrails a relatively new thing?

No, it has been exactly the same for decades, the only change has been the size of jet engines (producing bigger contrails), engine technology (burning fuel more efficiently in high bypass jet engines creates cooler exhaust which is more likely to condense before it mixes with the surrounding air) and the amount of air traffic (producing more contrails). Spreading contrails have been mentioned consistently through the history of aviation, including in the popular press.
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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.


NASA scientists have found that cirrus clouds, formed by contrails from aircraft engine exhaust, are capable of increasing average surface temperatures enough to account for a warming trend in the United States that occurred between 1975 and 1994. According to Patrick Minnis, a senior research scientist at NASA’s Langley Research Center in Hampton, Va., there has been a one percent per decade increase in cirrus cloud cover over the United States, likely due to air traffic. Cirrus clouds exert a warming influence on the surface by allowing most of the Sun’s rays to pass through but then trapping some of the resulting heat emitted by the surface and lower atmosphere. Using a general circulation model, Minnis estimates that cirrus clouds from contrails increased the temperatures of the lower atmosphere by anywhere from 0.36 to 0.54°F per decade. Minnis’s results show good agreement with weather service data, which reveal that the temperature of the surface and lower atmosphere rose by almost 0.5°F per decade between 1975 and 1994.



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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/

RPK.JPG
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:


http://onlinelibrary.wiley.com/doi/10.1002/joc.1418/abstract

US jet contrail frequency changes: influences of jet aircraft flight activity and atmospheric conditions

David J. Travis1,*, Andrew M. Carleton2, Jeffrey S. Johnson3, James Q. DeGrand4
Article first published online: 9 OCT 2006

DOI: 10.1002/joc.1418

International Journal of Climatology
Volume 27, Issue 5, pages 621–632, April 2007

In the United States, the dramatic increase in jet fuel usage and kilometers flown has led to speculation of a similar increase in jet contrails. However, contrail occurrence depends heavily upon the meteorological conditions near cruising altitudes (i.e. the tropopause, 10–12 km altitude). This study reports a contrail mid-season contemporary climatology for the coterminous United States (2000–2002), and compares the frequencies with those previously reported for an earlier (1977–1979) period, to determine spatial and seasonal contrail frequency changes. For both climatologies, contrail occurrence is derived from the analysis of high-resolution satellite imagery. Data on US jet aircraft flight activity were obtained to assess their relationship to contrail frequency, as were NCEP-NCAR reanalysis data to determine the changes in tropopause-level atmospheric conditions.

For the 2000–2002 period, contrails comprise a distinct high (low) frequency pattern in the East (West) halves of the United States. Seasonally, there is a contrail association with the latitudinal migration of the jet stream and a US-wide peak contrail frequency during winter (January). The inter-monthly variations in contrail frequency are significantly different from each other but show no association with variations in jet flight activity, indicating a greater role for meteorological conditions. Between the 1977–1979 and 2000–2002 periods, there were strong spatial and seasonal asymmetries to the contrail frequency change. These involve a cooling (warming) of the tropopause for the largest (smallest) frequency increases, which shows some association with the switch in positive and negative phases of the Arctic Oscillation. The role of upper tropospheric conditions and links to hemispheric-scale teleconnections should be considered when projecting contrail frequency changes and their future impacts on climate.

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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/


Where does it say that it will specifically can not reduce the number of Persistent Contrails? As far as I can see from what you have posted the actual effects on contrails are not specified.

This might help . . . Dr Minnis comments/responses are in red . . .


From: Minnis, Patrick (LARC-E302) [mailto:p.minnis@nasa.gov]
Sent: Saturday, November 10, 2012 11:01 PM
To: George B
Subject: Re: Persistent Contrails and Global Warming

Dear Mr. B,

I will try to answer your question below.

Patrick


On Nov 10, 2012, at 2:35 PM, George Berberich wrote:


Dr Minnis


Question . . .Dr Minnis . . . Can one say that global warming is potentially responsible for \
an increase in persistent contrails and contrail induced cirrus cloud banks?



I doubt that slightly higher temperatures due to climate change are responsible for an increase in persistent contrails and induced cirrus.
Higher temperatures in the troposphere would raise the altitude necessary for contrail formation, so that there would likely be slightly fewer contrails rather than more.

If so, what percentage could it represent of the total of the following factors?

1) Increased number and frequency of flights overall at altitudes above 30,000 feet
2) Larger and more powerful engines
3) More efficient engines
4) Global Warming




If there is more moisture in the high troposphere and lower stratosphere because of warming . . . and the temperature of the upper troposphere is warmer and the stratosphere is colder . . . so can this means .. . more persistent contrails in the stratosphere but fewer in the troposphere. . . ? Seems very negligible to me . . . I have never seen any publication which included the above discussion or speculation about the persistence of contrails based on global warming . . .see research cites below . . .


Persistent contrails rarely ever form in the stratosphere because it is too dry. A slight increase in humidity will not be sufficient to change this negligible frequency. More moisture in the upper troposphere could possibly lead to thicker contrails, but not more of them.



Thanks for your time

http://www.realclimate.org/index.php...osphere-warms/

http://www.ncdc.noaa.gov/cmb-faq/globalwarming.html
http://junkscience.com/2012/05/17/is...lobal-warming/


http://earthobservatory.nasa.gov/New...w.php?id=24432

Sent from my iPad

Yours Truly

George B
Colonel USAF Retired

***************************************************************************************
Patrick Minnis, PhD
MS 420
NASA Langley Research Center
Hampton, VA, USA 23681-0001
phone: 757-864-5671 fax: 757-864-7996 email: Patrick.Minnis-1@nasa.gov
homepage: http://www-pm.larc.nasa.gov
"humilitas est veritas"
*****************************************************************************************

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Ross Marsden

Senior Member.
Last paragraph of Box 8.1...

Overall, since the TAR, confidence has increased in the conventional view that the distribution of RH changes little as climate warms, particularly in the upper troposphere. Confidence has also increased in the ability of GCMs to represent upper-tropospheric humidity and its variations, both free and forced. Together, upper-tropospheric observational and modelling evidence provide strong support for a combined water vapour/lapse rate feedback of around the strength found in GCMs (see Section 8.6.3.1.2).
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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":
Satellite measurements also indicate that the globally averaged upper tropospheric relative humidity has changed little over the period 1979–2010 while the troposphere has warmed, implying an increase in the mean water vapour mass in the upper troposphere.
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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

The SAC states that a contrail forms during the plume expansion process if the mixture of exhaust gases and ambient air briefly reaches or surpasses saturation with re- spect to liquid water. The fact that the mixture must reach water saturation to form a visible contrail is the only empirical component of the thermodynamic approach, and it is the only component that is related to the ice-forming properties of emitted Aitken-mode soot particles and the ultrafine liquid particles that form prior to the formation of contrails. That is, these plume particles act primarily as cloud condensation nuclei and are poor ice-forming nuclei, at least prior to water activation. Small differences in the assumed ice nucleation behavior of the soot do not significantly affect the SAC for visible contrail formation (Kärcher et al. 1996).
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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

The SAC states that a contrail forms during the plume expansion process if the mixture of exhaust gases and ambient air briefly reaches or surpasses saturation with re- spect to liquid water. The fact that the mixture must reach water saturation to form a visible contrail is the only empirical component of the thermodynamic approach, and it is the only component that is related to the ice-forming properties of emitted Aitken-mode soot particles and the ultrafine liquid particles that form prior to the formation of contrails. That is, these plume particles act primarily as cloud condensation nuclei and are poor ice-forming nuclei, at least prior to water activation. Small differences in the assumed ice nucleation behavior of the soot do not significantly affect the SAC for visible contrail formation (Kärcher et al. 1996).
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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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