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Contrails over Europe

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Contrails over Europe

Old 24th Jan 2021, 09:09
  #21 (permalink)  
 
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So much is said about 'clouds'. Please note the careful difference that I pointed out between water droplet clouds and ice particle clouds. (They are very, very different. I know, I have done research flights into them. And any turboprop-pilot-wanting-to-be-a-jet-pilot can also confirm that they are very different!!)

Water droplet clouds are low level, more extensive and have a large 'greenhouse' effect. They also reflect solar radiation, but as they are more extensive and only reflect that solar radiation during the day, the overall effect is warming. And thank goodness for that, or else our planet would mostly be uninhabitable.

Ice particle clouds are very high and not nearly as extensive as the low level water droplet clouds. Being ice and very high, the reflect a lot of solar radiation before it is able to get into the more dense lower air and warm it up. Being relatively sparse and very high they have a very small 'greenhouse' effect.

Then there's the comment about contrails (which, as has been pointed out, become 'ice particle clouds' within a second or so of being formed):
But they trap heat radiating from the earth's surface at night
I can assure you that there are (in normal circumstances) many, many, many more contrails on the daytime side of the earth than on the night-time side of the earth. (Been there, seen that!) So that minimal night-time effect from any one contrail is reduced further by the fact that there are far less of them. The daytime cooling effect of the reflected solar radiation is increased further by the fact that there are many more of them.

That brings us back to:
If you are worried about global temperature rises and ice melt, we need more airliners flying!!
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Old 24th Jan 2021, 15:20
  #22 (permalink)  
 
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There was a BBC Horizon programme some years ago on the subject of "Global Dimming". It examined the effect of contrails on climate change. The research was instigated post 9/11 when the effect of having no contrails was noticed.
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Old 24th Jan 2021, 15:37
  #23 (permalink)  
 
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Visual Impact

Putting aside all of the global warming arguments (which are important), there is also the visual impact of contrails. They can be persistent, spread out and change the appearance of the sky from the ground, in fact making it less ‘blue’, more grey/white. I have noticed the difference over the last year.
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Old 24th Jan 2021, 15:39
  #24 (permalink)  
 
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This last year there was an increase in melting of ice in Greenland because of increased sunshine. Guess what?! There were very, very few airliners on those northerly trans-Atlantic routes that cross Greenland last summer, meaning a loss of all of those cirrus clouds (contrails) and hence more sunshine and more ice melting.
You are confusing causation and correlation. There was less traffic AND there was an increase in ice melt, you have not shown and probably will not find a causative link. Your deductive reasoning is incomplete in that there are other factors you have not considered.

Then there's the comment about contrails (which, as has been pointed out, become 'ice particle clouds' within a second or so of being formed):
That depends. Sometimes the ice crystals persist, at other times they evaporate, dumping water vapour into the atmosphere, water vapour which in itself is a potent greenhouse gas.
I can assure you that there are (in normal circumstances) many, many, many more contrails on the daytime side of the earth than on the night-time side of the earth. (Been there, seen that!)
Have you never wondered where they went? And what happened to the water vapour?


If you are worried about global temperature rises and ice melt, we need more airliners flying!!
ignoring the NOx, CO2 et al which add to the greenhouse effect.
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Old 24th Jan 2021, 17:20
  #25 (permalink)  
 
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Originally Posted by beardy View Post
... Sometimes the ice crystals persist, at other times they evaporate, dumping water vapour into the atmosphere, water vapour which in itself is a potent greenhouse gas.
...
Let me explain how those contrails form. The aeroplane does not emit that water to forms the contrails, The aeroplane disturbs moisture that is already in the air causing it to condense and form the contrail. Watch on days where there is a very dry upper atmosphere, You can easily see on those dry days how short the contrail 'tails' on aeroplanes are. Hopefully that has helped you a bit?

Regarding the comment:
I can assure you that there are (in normal circumstances) many, many, many more contrails on the daytime side of the earth than on the night-time side of the earth. (Been there, seen that!)
... you say:
Originally Posted by beardy View Post
...
Have you never wondered where they went? And what happened to the water vapour?
...
Ummm...!! - There - are - less - contrails - at - night - ... - because - there - are - less - aeroplanes - at - night.
Just try listening to any ATC frequency at 2pm and compare with 2am.
Those contrails never 'went' anywhere, they were never created!

If you are worried about global temperature rises and ice melt, we need more airliners flying!!
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Old 24th Jan 2021, 18:26
  #26 (permalink)  
 
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et me explain how those contrails form. The aeroplane does notemit that water to forms the contrails, The aeroplane disturbs moisture that is already in the air causing it to condense and form the contrail. Watch on days where there is a very dry upper atmosphere, You can easily see on those dry days how short the contrail 'tails' on aeroplanes are. Hopefully that has helped you a bit?
Ah, now I see your confusion. The contrails are formed from the water produced from burning hydrocarbons in the fuel. The carbon produces CO2 and the hydrogen produces H2O. Look out the window and you will see that they form in the exhaust from the engines, not at the wing tips. Four from a four engined aircraft, two from a twin which then merge. They are not the same as the condensate produced by wing tip vortices. I take it that you have never been in trail behind a contrailing heavy. Contrail formation is an interesting topic involving partial pressures of both water and ice at the temperature and pressure at altitude. The saturation point of the different states of water are different. Look at ice formation overnight in frosty weather, water vapour sublimates directly into hoar frost (similar to contrail and ice clouds) without ever forming dew (similar to wet cloud.)

Ummm...!! - There - are - less - contrails - at - night - ... - because - there - are - less - aeroplanes - at - night.
Just try listening to any ATC frequency at 2pm and compare with 2am.
Those contrails never 'went' anywhere, they were never created!
Quite correct there are fewer aircraft, especially shorthaul, at night and so fewer contrails. However contrails do form at night and do disperse with or without daylight. When they disperse they do increase the proportion of water vapour in the atmosphere.

Last edited by beardy; 24th Jan 2021 at 18:49.
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Old 24th Jan 2021, 18:45
  #27 (permalink)  
 
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Originally Posted by beardy View Post
Ah, now I see your confusion. The contrails are formed from the water produced from burning hydrocarbons in the fuel. The carbon produces CO2 and the hydrogen produces H2O. Look out the window and you will see that they form in the exhaust from the engines, not at the wing tips. Four from a four engined aircraft, two from a twin which then merge.
...
I see ... ... ...
So I suppose those very short contrails are when the aeroplane is not using much fuel and the long contrails are when they are using a lot?

(Does a contrail 'come out of the engine', or does it forms in the disturbed air behind that high speed exhaust air? But I really do like the idea that the length of the contrails could be an indicator of the engine power settings!!)

However contrails do form at night
Yes, and they look very pretty in the moonlight, especially when you see them close up.
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Old 24th Jan 2021, 18:55
  #28 (permalink)  
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Here's an open access article explaining in detail how contrails form. As a rough summary, the soot particles in the exhaust are nucleation site for ice crystals to develop from the water vapor in the exhaust. The ice crystals grow further from ambient water vapor.
[email protected]/articles/s41467-018-04068-0
Replace @ with dot
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Old 24th Jan 2021, 18:58
  #29 (permalink)  
 
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Quite correct they form in the diluted exhaust efflux. And no the dispersion rate has nothing to do with power setting, I'm not sure why you would think so. The dispersion of contrails is due to evaporation of the ice crystals. It is all within the scope of A level physics (or it used to be) not that complicated really.
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Old 24th Jan 2021, 19:18
  #30 (permalink)  
 
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Here is an interesting piece about contrail formation and dissipation :

https://www.google.com/url?sa=t&sour...ies-sQdSJhRQq_
Or perhaps in layman's terms

https://en.m.wikipedia.org/wiki/Contrail
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Old 25th Jan 2021, 10:17
  #31 (permalink)  
 
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With some basic observations you can figure out that length and persistency of contrails depends pretty much on weather. I live on south side of Alps and contrail behavior is one of indicators to do my own forecast. Short, tiny contrails mean air in upper troposphere is generally dry and that is common when we have dry, cold northerly wind across the Alps, bringing sunny, dry and cooler weather. When contrails become long and in particular, when they spread into wide swaths of cirrus-like clouds and persist, that means moist air is coming, forecasting bad, (means cloudy, possible rainy) weather is getting in. It works every time. No rocket science here.
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Old 25th Jan 2021, 16:27
  #32 (permalink)  
 
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This last year there was an increase in melting of ice in Greenland because of increased sunshine. Guess what?! There were very, very few airliners on those northerly trans-Atlantic routes that cross Greenland last summer, meaning a loss of all of those cirrus clouds (contrails) and hence more sunshine and more ice melting.
From Carbon Brief

However, unlike in 2019, Greenland has actually had a relatively “normal” year with regard to ice changes at its surface. Yet losses via the breaking off of icebergs remain at the high end compared to the early years of the satellite record, which stretches back to the late 1970s.

The ice sheet ends the season losing about 152bn tonnes when accounting for both surface melting and discharge of icebergs. This means that the ice sheet is continuing to lose ice, though at a slower rate than seen in 2019.
No mention of greater insolation, but emphasis is given to stable high pressure and warmer air.
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Old 26th Jan 2021, 11:26
  #33 (permalink)  
 
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And it is very important that airliners stay at the "crossover altitude", so they get as fast as possible from A to B.... so we can save time before the next flight.
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Old 26th Jan 2021, 12:15
  #34 (permalink)  
 
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Question. Why does the aviation world refer to the deposition (of ice) as sublimation?
Sublimation is the change directly from solid to gas.
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Old 26th Jan 2021, 15:47
  #35 (permalink)  
 
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I apologise for having used the wrong phrase I meant desublimation for gas to solid phase transition and sublimation for evaporation from solid to gas all without the intervening liquid phase.
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Old 26th Jan 2021, 17:31
  #36 (permalink)  
 
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Apologies if my question came across as a personal attack, it certainly wasn't intended that way.
Sublimation is erroneously applied in many aviation publications and instructional material e.g.
https://www.skybrary.aero/index.php/...on_on_Aircraft

Curious how something so wrong is just accepted.
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Old 26th Jan 2021, 17:50
  #37 (permalink)  
 
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No need to apologise, I didn't take it as a personal attack.
The term was used for phase transition both ways on my university course, the emphasis being on the missing out of the liquid phase by manipulating the temperature and/or pressure. However, I accept that the meaning may have changed over the (many) years and useage.
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Old 1st Feb 2021, 15:57
  #38 (permalink)  
 
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I watched three contrails today (there weren't many).

The first was a long contrail that lingered for a long, long time.

Some hours later, the next was very short. It disappeared a short way behind the aeroplane.

A few hours later another one was very long, but did not linger nearly as long as the first.

All were high, on trans-Atlantic tracks (I checked the last one, it was a KLM Cargo 747 going to Chicago).

Were they all emitting water differently? Was the second one emitting very little water? How?
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Old 1st Feb 2021, 16:45
  #39 (permalink)  
 
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If you want to do some work finding out, here's a long answer for you:

How Well Can Persistent Contrails Be Predicted
"There are two atmospheric conditions necessary for persistent contrails. First, the so called Schmidt-Appleman criterion must be fulfilled, which is a pure thermodynamic criterion that rules whether contrail formation is possible in a given situation or not. This criterion covers both short-term (lifetime seconds to a few minutes) and persistent contrails. Thus a second condition is required for persistent contrails: the ambient air must be in a state of ice supersaturation, that is, the relative humidity with respect to ice, RHi must exceed 100%"

Although there are other articles that cover the same topic
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Old 1st Feb 2021, 19:26
  #40 (permalink)  
 
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Different flight levels?
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