What exactly causes vapour trails?
I'll get me coat......
Thread Starter
Join Date: Sep 2002
Location: Gold Coast, Australia.
Age: 51
Posts: 532
Likes: 0
Received 0 Likes
on
0 Posts
What exactly causes vapour trails?
Can someone please explain exactly how the vapour trails that you see behind jets at flight levels are formed?
Always behind curious about that one!
Cheers.
That was supposed to say always 'been' curious about that one!
Always behind curious about that one!
Cheers.
That was supposed to say always 'been' curious about that one!
Join Date: Oct 2000
Location: Berkshire, UK
Age: 79
Posts: 8,268
Likes: 0
Received 0 Likes
on
0 Posts
There's a significant opinion, mainly in the US, that they're caused by chemicals being sprayed on the unknowing population beneath. A neighbour of mine, writing to the local newspaper, declared that they are polluting exhaust fumes from jets... which merge together and form the dark, overcast, clouds which we see so often in the UK.
I don't recall mention of either of these reasons when I studied Met!
I don't recall mention of either of these reasons when I studied Met!
Join Date: May 2002
Location: Australia
Posts: 2,242
Likes: 0
Received 0 Likes
on
0 Posts
Warm, moist air being flung out into extremely dry and cold air.
Warm, moist air then has to vapourise and becomes visible, (usually). It is all to do with the ability, or non abilitiy, of cold, dry air to absorb warm moist air. Basic physics really.
Warm, moist air then has to vapourise and becomes visible, (usually). It is all to do with the ability, or non abilitiy, of cold, dry air to absorb warm moist air. Basic physics really.
I'll get me coat......
Thread Starter
Join Date: Sep 2002
Location: Gold Coast, Australia.
Age: 51
Posts: 532
Likes: 0
Received 0 Likes
on
0 Posts
Still not quite enough info?
Thanks BlueEagle, not quite sure where the 'moist' air comes from though. I understand the concept as in Met where warm moist air is pushed up into the atmosphere, cools and so condenses and forms water vapour (clouds). But all the engine is doing is compressing the air, heating it and throwing it out the back! Where does the moisture come from? There is probably an obvious answer here that I'm missing, baring in mind I don't go anywhere near flight levels in my helicopter!
Moderator
If I scratch my head from a long time ago, the complete combustion of a hydrocarbon in the presence of sufficient oxygen produces carbon dioxide and water. In the real world this generally is not achieved completely and there are lots of other combustion products, carbon monoxide, soot plus various products which come from impurities in the fuel (in this case).
However, there is LOTS of water vapour pumped out the back of the engine ....
However, there is LOTS of water vapour pumped out the back of the engine ....
Join Date: Jun 2002
Location: Germany
Posts: 407
Likes: 0
Received 0 Likes
on
0 Posts
not so fast....
there are 2 different kind of contrails airplanes can leave behind.
1) condensation contrail
-as described above
2) aerodynamic contrail
- The reduced pressure produced by air flowing over the wing causes the air to cool. This cooling may supersaturate the air
How can you tell the difference? Aerodynamic contrails disappear quickly - meaning they are very short compared to the longer condensation contrails
there are 2 different kind of contrails airplanes can leave behind.
1) condensation contrail
-as described above
2) aerodynamic contrail
- The reduced pressure produced by air flowing over the wing causes the air to cool. This cooling may supersaturate the air
How can you tell the difference? Aerodynamic contrails disappear quickly - meaning they are very short compared to the longer condensation contrails
Join Date: Jul 2000
Location: 1060 West Addison
Posts: 67
Likes: 0
Received 0 Likes
on
0 Posts
To confuse the issue further, how come if the wake turbulence from the wing is strong enough to knock a buzzard from a sh*t wagon, it doesn't seem to disturb the nice, regular contrail pattern we see on those lovely sunny days?
Answers on a postcard please.....
Answers on a postcard please.....
Join Date: Jun 2002
Location: Germany
Posts: 407
Likes: 0
Received 0 Likes
on
0 Posts
uhm, because contrails constist of water vapor and not solid matter?
If you get a close look at one of those contrails, you'll see rotation in them. At least with the aerodynamic contrails.
Infact, the reason the aerodynamic contrails dont last long is because, and i qoute from my meteorology book, "this type of trail usually disappears quckly in the turbulent wake of the aircraft"
oh, and before i forget,
the wake turbulence sinks at a rate of about 900fpm.
This means, and i'm speculating now , that the turbulence can't get into the condensation contrail, thus its not "disturbed"
If you get a close look at one of those contrails, you'll see rotation in them. At least with the aerodynamic contrails.
Infact, the reason the aerodynamic contrails dont last long is because, and i qoute from my meteorology book, "this type of trail usually disappears quckly in the turbulent wake of the aircraft"
oh, and before i forget,
the wake turbulence sinks at a rate of about 900fpm.
This means, and i'm speculating now , that the turbulence can't get into the condensation contrail, thus its not "disturbed"
stings like a bee
Join Date: Nov 2001
Location: Buckinghamshire England
Posts: 70
Likes: 0
Received 0 Likes
on
0 Posts
BGPM - Think of it in terms of the wake from a ship. Turbulent to be in but slow moving relative to its environment.
When aircraft trail condensation plumes from their wing tips, the condensation takes place in the low-pressure core of the vortex generated by each wing. The two, normally invisible, counter-rotating vortices trail behind the aircraft. The exhaust from the engines is swept into this rotation, which explains why contrails always appear as a pair of rolls of condensation, regardless of the number of engines.
Anyone heard of a Distrail? If the aircraft is flying above a layer of thin cloud, the vortices may force warmer air down from the higher level. This can be sufficient to disperse the cloud beneath the path of the aircraft, so forming a Distrail.
Finally just to exhaust everything I know about this subject. An aircraft flying through supercooled water droplets may initiate freezing in the cloud, producing a clear channel when the ice crystals fall out into the lower air.
When aircraft trail condensation plumes from their wing tips, the condensation takes place in the low-pressure core of the vortex generated by each wing. The two, normally invisible, counter-rotating vortices trail behind the aircraft. The exhaust from the engines is swept into this rotation, which explains why contrails always appear as a pair of rolls of condensation, regardless of the number of engines.
Anyone heard of a Distrail? If the aircraft is flying above a layer of thin cloud, the vortices may force warmer air down from the higher level. This can be sufficient to disperse the cloud beneath the path of the aircraft, so forming a Distrail.
Finally just to exhaust everything I know about this subject. An aircraft flying through supercooled water droplets may initiate freezing in the cloud, producing a clear channel when the ice crystals fall out into the lower air.
Ecce Homo! Loquitur...
Join Date: Feb 2002
Location: Just becoming established 25
Posts: 146
Likes: 0
Received 0 Likes
on
0 Posts
I noticed the other day two wide bodies, looked like 767s following more or less the same track,and very close together heading towards the Belfast VOR and from what I could tell more or less at the same level. The AC in front was trailing like mad yet the one behind had no trail at all.
Most of the other AC that day were also trailing.
How come the second AC had no trail?
Most of the other AC that day were also trailing.
How come the second AC had no trail?
Join Date: Jan 2002
Location: CYHU
Posts: 25
Likes: 0
Received 0 Likes
on
0 Posts
I'll get me coat......
Thread Starter
Join Date: Sep 2002
Location: Gold Coast, Australia.
Age: 51
Posts: 532
Likes: 0
Received 0 Likes
on
0 Posts
Awesome photo 152captain. Not too often you see photos from above.
Thanks to everyone, this is my first post, quite amazed at how quickly the replies came in!
Cheers.
Thanks to everyone, this is my first post, quite amazed at how quickly the replies came in!
Cheers.
Join Date: Aug 2002
Location: Stockport, Cheshire, U.K.
Posts: 13
Likes: 0
Received 0 Likes
on
0 Posts
B767 vapour
When i was coming home from Italy in June, I was in a britannia boeing 767-300 taking off from Pisa. I was near the window over the wing and noticed a strange vapour trail coming off the top of the engine as the aircraft rotated quite quickly. At first i thought something was leaking out of the engine but then realised it was only some sort of vapour trail coz it vanished really quickly.
apparantly its quite common and it shocks some passengers into thinking the engines about to blow up.
apparantly its quite common and it shocks some passengers into thinking the engines about to blow up.
Join Date: Apr 2002
Location: North Carolina, USA, Planet Earth
Posts: 75
Likes: 0
Received 0 Likes
on
0 Posts
Heathrow D-
Your neighbor isn't totally daft-it seems that contrails do indeed sometimes merge into overcast-see this:
http://www.atmos.berkeley.edu/news/c...ul2002.article
Your neighbor isn't totally daft-it seems that contrails do indeed sometimes merge into overcast-see this:
http://www.atmos.berkeley.edu/news/c...ul2002.article
stings like a bee
Join Date: Nov 2001
Location: Buckinghamshire England
Posts: 70
Likes: 0
Received 0 Likes
on
0 Posts
Vim - Yes the likelihood or otherwise of contrails is forecastable and depends entirely on atmospheric conditions on the day.
Upper air soundings are taken by radio-sonde balloons at regular intervals from many locations and the resultant readings enable weather forecasters to determine the characteristics of the atmosphere up to very high altitudes and hence predict the types of cloud formation, from what altitude clouds will form etc. etc.
Hope this helps.
DoB
Upper air soundings are taken by radio-sonde balloons at regular intervals from many locations and the resultant readings enable weather forecasters to determine the characteristics of the atmosphere up to very high altitudes and hence predict the types of cloud formation, from what altitude clouds will form etc. etc.
Hope this helps.
DoB