PPRuNe Forums

Go Back   PPRuNe Forums > PPRuNe Social > Jet Blast
Forgotten your Username/Password?

Jet Blast Topics that don't fit the other forums. Rules of Engagement apply.


Reply
 
Thread Tools
Old 24th Oct 2010, 18:14   #1 (permalink)
 
Join Date: Feb 2008
Location: The Ethereal Land of Vintage Aviation
Posts: 110
Why Are Contrails More Vivid Some Days?

I snapped this photo a few days ago. You will see a contrail zipping across the bottom of the picture. It was a day when the sky was slashed with contrails.

There were some interesting cloud formations too. This vertical cloud (intersecting the horizontal contrail) looks like a contrail from an aerobatic airplane. I liked how it hung there suspended.....like a big piece of unravelled toilet paper!

My question is the title - why are contrails more vivid some days?


V2-OMG! is offline   Reply
Old 24th Oct 2010, 18:19   #2 (permalink)

Aviator Extraordinaire
 
Join Date: May 2000
Location: Oklahoma City, Oklahoma USA
Age: 67
Posts: 1,795
Shhhhhhhhhhh.

It's when the Chemtrails tanks are freshly filled. But don't tell anybody, mum's the word.















Actually it is due to the temperature at altitude, the colder, the more visible the contrail.
con-pilot is online now   Reply
Old 24th Oct 2010, 18:28   #3 (permalink)
 
Join Date: Jul 2006
Location: East of LGB
Age: 59
Posts: 462
Recently, over LA.



DANG IT..... I left my hat on the counter back in San Diego....

oh wait, here it is..... press on.
11Fan is online now   Reply
Old 24th Oct 2010, 18:46   #4 (permalink)
 
Join Date: Aug 2009
Location: England
Posts: 91
Psychrometry, A very complex subject.

Psychrometrics or psychrometry are terms used to describe the field of engineering concerned with the determination of physical and thermodynamic properties of gas-vapor mixtures. The term derives from the Greek psuchron (ψυχρόν) meaning "cold"and metron (μέτρον) meaning "means of measurement

Although the principles of psychrometry apply to any physical system consisting of gas-vapor mixtures, the most common system of interest is the mixture of water vapor and air, because of its application in heating, ventilating, and air-conditioning and meteorology. In human terms, our comfort is in large part a consequence of, not just the temperature of the surrounding air, but (because we cool ourselves via perspiration) the extent to which that air is saturated with water vapor

Psychrometrics - Wikipedia, the free encyclopedia

Lid
flying lid is offline   Reply
Old 24th Oct 2010, 18:47   #5 (permalink)
Cleverly disguised as a responsible adult
 
Join Date: May 2007
Location: On the western edge of The Moor
Age: 57
Posts: 1,018
Over the Irish Sea earlier this year


Overhead home!


One of the culprits!


Last edited by west lakes; 24th Oct 2010 at 18:57.
west lakes is offline   Reply
Old 24th Oct 2010, 19:12   #6 (permalink)
Ant
even ants need some lovin'
 
Join Date: Jan 2001
Location: Kent, UK.
Posts: 86
... and on a similar note, how can it be that an airliner at cruising altitude can produce no trail at all?? It's rare, but I've seen this a few times, and it implies that the air for some reason despite the altitude is above freezing so that water in the exhaust is not condensing to form a trail.
Ant is offline   Reply
Old 24th Oct 2010, 19:35   #7 (permalink)
 
Join Date: Feb 2008
Location: The Ethereal Land of Vintage Aviation
Posts: 110
Ant, wondering the same here.
V2-OMG! is offline   Reply
Old 24th Oct 2010, 19:49   #8 (permalink)
 
Join Date: May 2003
Location: South East England
Posts: 301
From The Times
January 25, 2008

Jet engine contrails can show whether it will rain

Paul Simons: Weather Eye

Why can you see your breath on a cold day? The air from your lungs is warm and moist and when this meets the cold air outside it condenses the invisible water vapour in your breath turns into water droplets and makes a small cloud. The same happens when your breath fogs up a cold bathroom mirror or a cold windscreen in a car.
The same sort of thing explains how white streaks of clouds are left behind from highflying aircraft jets. These contrails are produced by jets at altitudes above about 8km (5 miles). The water vapour that shoots out of a hot jet engine exhaust hits the cold air outside and condenses into a ribbon of cloud. Because the air at these altitudes is so cold, generally less than minus 40C (-40F), only a small amount of liquid is needed for condensation before it freezes into ice crystals.
Contrails can give clues to what the weather will bring. A lack of any contrails from the aircraft is a sign that the high altitude atmosphere is very dry and the weather could stay fine. Short contrails that disappear quite quickly are indicate that the air is fairly moist. And a persistent contrail shows that the air is very moist and possibly a sign of an approaching weather front and rain.

The Times
None of the above is offline   Reply
Old 24th Oct 2010, 20:02   #9 (permalink)
Cleverly disguised as a responsible adult
 
Join Date: May 2007
Location: On the western edge of The Moor
Age: 57
Posts: 1,018
Oddly enough there is a film on UK Sky TV about chemtrails!!
Must watch this to learn the truth
west lakes is offline   Reply
Old 24th Oct 2010, 20:50   #10 (permalink)
 
Join Date: Oct 1999
Location: Ireland
Posts: 634
QUOTE] how can it be that an airliner at cruising altitude can produce no trail at all?? It's rare, but I've seen this a few times,[/QUOTE]That was happening overhead today as the transatlantic traffic passed overhead, some were producing short trails, others none at all. There was a clue of course. The westbounds were producing contrails. Eastbounds were not.

My simplistic understanding is that contrails are formed when temperatures fall below minus 40C. Clearly today the westbounds were flying just inside that temperature range and the eastbound flights were outside it.

Obviously it's never as simple as that and the Times article mentioned moisture content of the air. Clearly that's another factor. Interestingly it was a cold crisp day here on the ground which appeared to point to lower moisture content. A quick check revealed a nice spread between the temperature and a very low dewpoint at the nearest big airport. Which appears to confirm my junk science hypothesis.

It was a beautiful day for flying which is all the more puzzling because my last day of the flying season was cancelled for bad weather???????????
corsair is offline   Reply
Old 24th Oct 2010, 20:52   #11 (permalink)
10W

PPRuNe Bashaholic
Moderator
 
Join Date: Jun 1997
Location: The Peoples Alcoholic Republic of Jockistan
Posts: 1,403
Quote:
One of the culprits!
Phew !! For a moment I thought you were going to blame me Westie
__________________
10 West
UK ATC'er
Old enough to know better, young enough to carry on regardless.

10w@pprune.org
10W is offline   Reply
Old 24th Oct 2010, 20:55   #12 (permalink)
Cleverly disguised as a responsible adult
 
Join Date: May 2007
Location: On the western edge of The Moor
Age: 57
Posts: 1,018
10W nah you just tell them where to go!


(though it was in your airspace!)
west lakes is offline   Reply
Old 24th Oct 2010, 21:43   #13 (permalink)
10W

PPRuNe Bashaholic
Moderator
 
Join Date: Jun 1997
Location: The Peoples Alcoholic Republic of Jockistan
Posts: 1,403
You need to send me the date you took the picture Westie. I need to find out who was doing such untidy controlling (and hence contrailing)
__________________
10 West
UK ATC'er
Old enough to know better, young enough to carry on regardless.

10w@pprune.org
10W is offline   Reply
Old 24th Oct 2010, 21:50   #14 (permalink)
 
Join Date: Jan 2000
Location: Wickford,Essex,England
Posts: 91
I believe that on the tephigrame (spelling?) there is a line marked the matra line above which you gat contrails, cannot rember the details but to do with the enviromental lapse rate, dew point etc.
Steamhead is offline   Reply
Old 24th Oct 2010, 21:53   #15 (permalink)
 
Join Date: May 2001
Location: Newcastle/UK
Posts: 83
I think they are only produced when the engines are running.
tony draper is offline   Reply
Old 24th Oct 2010, 22:26   #16 (permalink)
 
Join Date: Jul 2003
Location: at the edge of nowhere, dogleg England
Age: 31
Posts: 225
tony

Also, the number of contrails I saw when I first left India astonished me. That's when I realised the impact of what I'd always read as "hot-and-high" conditions in the subcontinent. I figure it's (relatively) hot even at that altitude in all but winter. And for most parts of India (Bombay and southwards) "winter" is at worst 15 degrees above zero on the ground.
BombayDuck is offline   Reply
Old 24th Oct 2010, 22:47   #17 (permalink)
Registered User **
 
Join Date: Aug 2005
Location: Sydney
Posts: 628
Interesting web site which explains that it depends on the moisture content of the air that the aircraft is flying through.
World War two pilots wished there was no such things as contrails either.Nothing like a bit of advertising to help the guys on the ground.
RedTBar is offline   Reply
Old 24th Oct 2010, 22:57   #18 (permalink)
Psychophysiological entity
 
Join Date: Jun 2001
Location: Tweet Rob_Benham Famous author. Well, slightly famous.
Age: 75
Posts: 3,705
Apropos nothing much, I recall reading in me notes, that the coldest air temperatures were found over the equator. -80 if I haven't misremembered.

We got permission to drop 500' one nice day. I'd seen a lovely tubular trail a tad below us. We flew through that corkscrew tunnel for quite a few miles - totally stunning, since it had zero airspeed.
Loose rivets is offline   Reply
Old 25th Oct 2010, 00:32   #19 (permalink)
 
Join Date: Apr 2002
Location: Hong Kong
Age: 47
Posts: 1,259
It depends what we are putting in the mix down the chem plant. Since we started outsourcing a lot of the production to India & China we've had a few issues with quality control due to the inspectors being downsized and outside auditors are corrupt - we've been really worried the mix might not be up to strength. Anyway we've been spraying a bit more until the % strength is back to what it should be.
If that batch that was bright red had got out though man - there would have been quite a palaver!
Load Toad is offline   Reply
Old 25th Oct 2010, 04:59   #20 (permalink)
 
Join Date: Feb 2008
Location: The Ethereal Land of Vintage Aviation
Posts: 110
Thank-you all, for your answers and links.

Looking up will never be the same again.
V2-OMG! is offline   Reply
Reply
 
 
 


Thread Tools


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT. The time now is 03:44.


vBulletin® v3.8.7, Copyright ©2000-2014, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
1996-2012 The Professional Pilots Rumour Network