aeroplane vapour trails.

[funkymoped]

why do earoplane vapour trails break into a "scar" shape ?
its as though they were made by a pulse jet engine. an almost unbroken trail with smaller rings loosle wrapped around the main trail.

i know they are made from a constant high speed engine, but cant work out why they break up as they do...

thanks in advance..
:-)

[nickmo]

I think its to do with the fact that as contrails (posh proper name) are water vapour and ice, the trails form specific 'clumps' that attract one another as they form.

As the air that the plane flies through needs to be cold enough for the vapour to form the ice that we see - as the plane is moving through cold air, the heat of the exhaust can only heat the air intermittently as it passes through - so we see the lumps you describe..

There is a lot of debate as to whether the planes should fly lower in warmer air so they do not form contrails as it has been proven through research that the contrails are adding to global warming.

The downside is that the lower flight path in warmer -and so denser - air increases the amount of CO2 emitted as the engines have to work harder, so one is a trade off agaisnt the other for about the same result.

[Clanad]

The upper winds at the altitudes normally used by passenger jets (around 35,000 to 45,000 feet above sea level) create the patterns. The only aircraft to use a pulse jet engine (and it was a hybrid turboramjet) was the SR-71 Blackbird, which isn't used any longer (with the exception of 2 on loan to NASA) since satellites have taken over its primary spy function... That engine/airframe combination did produce some interesting contrails, though only on it's climb since it operated around 85,000 feet above sea level...

[nickmo]

Hi clanad - have you seen the theory about Aurora ? Some info there and also a pic of an odd vapour trail, and there are loads of sites like Area51.com that speculate whether the thing exists or not.

The link speculates whether there was a flight over Scotland, and on that note, I watched an extremely high level vapour trail forming in a wide circular pattern over the East coast of Scotland about 4 weeks ago (while I was at an event - not 'cos i was plane spotting - - the 'plane was circling for an hour +, and leaving some impressive trails in huge wide arcs which i'd never seen before, but I couldn't make out the shape of the 'plane - as you can do with normal large jets, so I presume it was a military flight of some sort.

Of course, could just be aliens . . . .

[Clanad]

I'd rather think your first supposition was more nearly correct, nickmo as opposed to aliens, that is. How many years did SR-71 and F-117's fly before being acknowledged? Technology marches on, so to speak!

[Clanad]

Nice web site, by the way, nickmo... thanx for that!

[nickmo]

Hi C - this is also interesting for info on the spyplane scenario if of interest to you - also another weird contrail here and as you say, the replacements are likely to be already flying - and the next generation is probably being planned now anyway, so the public will always be one model behind.

Still like the aliens bit though . . . .

[nickmo]

clanad - just a note re the circling plane comment - found this here so any opinions about what it was all about look as if they would be appreciated.: just glad its not only me that 'sees things '. . !

Tata for now.

[Catso]

nickmo, contrails don't add to global warming, they reduce it. See 'global dimming' (I think it's called). There was a Horizon programme all about it. The (invisible) gases produced along with the contrail do add to global warming; they seem to have a disproportionate effect being released so high in the atmosphere.

To answer the OP, the aircraft vortices act upon the contrail immediately after the aircraft, which is why (if you look closely) you don't get a nice even continuous 'stream', but a pulsed/fluffy effect.

[nickmo]

Hi catso - global dimming - I remember the programme - 3 days without contrails in the Western US after 9/11 led to a rise in temp of 1 degreeC, if I recall - but research into the effect of the trails which seems to be ongoing is that the reflection properties of the vapopur lead to a rise in the global temps. Extract from Wikipedia:

'Contrails, by affecting cloud formation, can act as a radiative forcing. Various studies have found that contrails trap outgoing longwave radiation emitted by the Earth and atmosphere (positive radiative forcing) at a greater rate than they reflect incoming solar radiation (negative radiative forcing). Therefore, the overall effect of contrails is a warming.[1] However, the effect varies daily and annually, and overall the size of the forcing is not well known: globally (for 1992 air traffic conditions), values range from 3.5 mW/m� to 17 mW/m�. Other studies have determined that night flights are most responsible for the warming effect: while accounting for only 25 percent of daily air traffic, they contribute 60 to 80 percent of contrail radiative forcing. Similarly, winter flights account for only 22 percent of annual air traffic, but contribute half of the annual mean radiative forcing.[2]'

I think the door is open to this to be honestl. Again Wikipedia has a good page on dimming if you have few ins to spare.

Quite a topical subject to me as I am all for promoting local shopping etc so why accept imported - flown in - goods? etc etc