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Atmospheric Effects On Contrails  
User currently offlineLogan22L From , joined Dec 1969, posts, RR:
Posted (10 years 4 days 11 hours ago) and read 1454 times:

I've looked through some old posts on contrails, but couldn't really find the answers I am looking for. The other day I saw a contrail that extended from horizon to horizon (of course, near Boston, that isn't as far as some places), whereas today I just saw one that quickly dissipated about 1,000-2,000 feet or so behind the aircraft. The weather here on earth was pretty similar both days, so I'm wondering what factors in the stratosphere (e.g., humidity) are influencing the longevity of the contrails. Both contrails were well defined, so it didn't appear that turbulence was a factor, and both aircraft were clearly at cruising altitude. Thanks for any help,

John

8 replies: All unread, jump to last
 
User currently offlineWomBat151 From Netherlands, joined Aug 2004, 36 posts, RR: 0
Reply 1, posted (10 years 4 days 9 hours ago) and read 1397 times:

The contrails are comparible to the window drops at your home. When it's cold outside, and you breathe agains the window, little drops will appear on the window.
An airplane's exhaust gasses are also hot, and this way humidity concentrates in the air. It's a sort of artificial clowd. Clowds dissolve faster when there is less moisture in the air. When there's a lot of moisture, the clowd stays longer because there's no room for the moisture to dissolve in the air.

The short trail is because of the air up there was much more dry as in the other case.

[Edited 2004-08-26 19:17:57]


Ian @ EHAM (AMS), 3,1NM of SPY VOR radial 205
User currently offlineInvictus From Germany, joined Aug 2004, 64 posts, RR: 0
Reply 2, posted (10 years 4 days 9 hours ago) and read 1387 times:

CLOWDS

What on earth (or in heaven) are clowds...?  Sad



The captain of my soul.
User currently offlineLogan22L From , joined Dec 1969, posts, RR:
Reply 3, posted (10 years 4 days 8 hours ago) and read 1378 times:


I guess it's surprising to me that the humidity in the stratosphere could change so significantly, since it starts more than six miles up. Any atmospheric experts know what range of humidity (or relative humidity, as appropriate) is present at this altitude, and what change is needed to drastically affect the length of a contrail as I described in my initial post? Thanks,

Logan


User currently offlineKlaus From Germany, joined Jul 2001, 21442 posts, RR: 54
Reply 4, posted (10 years 4 days 8 hours ago) and read 1373 times:

Contrails are formed largely because of additional water vapour introduced into the air by the combustion of hydrocarbon fuel. The hydrogen contained in the fuel is burned with oxygen from the ambient air to ordinary water vapour.

This pushes the relative humidity of the air upwards. And if ambient humidity had been high enough to begin with, water will start to condense (and possibly freeze) and thus form contrails. If the ambient air is moist enough, the contrails will not evaporate/sublimate again for a while.

Humidity is usually measured in percent of the vapour capacity of the air. While the total capacity will decrease with temperature/pressure, air at altitude can still have up to 100% relative humidity.


User currently offlineGoboeing From United States of America, joined Jun 2000, 2694 posts, RR: 15
Reply 5, posted (10 years 4 days 8 hours ago) and read 1370 times:

Logan22L,
I saw the contrail you might be talking about. Was it Tuesday morning at 7 or 8 AM? It was the longest contrail I have ever seen...it just kept going in either direction!

747 contrails are my favorite; they leave behind curly strands of cloud that gradually get wrapped up and go away. Neat looking.

Nick


User currently offlineSATL382G From , joined Dec 1969, posts, RR:
Reply 6, posted (10 years 4 days 8 hours ago) and read 1368 times:

Length of a contrail could also be affected by the aircraft climbing or descending through different layers of atmosphere.

SATL382G


User currently offlineLogan22L From , joined Dec 1969, posts, RR:
Reply 7, posted (10 years 4 days 7 hours ago) and read 1361 times:


Klaus: Thanks for the reply; as a chemist and environmental scientist I understand the chemistry part, but I am surprised that the humidity fluctuations in the stratosphere would be enough to so drastically affect contrail length.

Goboeing: I live in Boston, so it doesn't seem like the contrail you saw was the same as the one I saw, but I believe that it was on Tuesday, only later in the morning.

Logan


User currently offlineKlaus From Germany, joined Jul 2001, 21442 posts, RR: 54
Reply 8, posted (10 years 4 days 7 hours ago) and read 1362 times:

Logan22L: Klaus: Thanks for the reply; as a chemist and environmental scientist I understand the chemistry part

...probably a lot better than I do, actually. Chemistry was never really my strongest suit.  Wink/being sarcastic I just try to get a hang of the fundamentals as far as possible.


Logan22L: but I am surprised that the humidity fluctuations in the stratosphere would be enough to so drastically affect contrail length.

Well, you can have "natural" clouds at all the same altitudes, so the variations are certainly there already. Aircraft only skew them far enough to sometimes get a visible effect.


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