This morning on the way to work I noticed whatmust ahve been ten trails in teh sky on an otherwise perfectly clear day. Perhaps they are there everyday and I just happened to look up. Perhaps it was the contrast with the perfectly clear sky. there was one even in process. A lady at work said they were vapor trails but I have a hard time remembering ever seeing this many. and not all planes make them to my knowledge. does nyone know about this? are they really vapor trails? if not, what are they?

it's sodium pentathal.

__________________
Jason
Lynn Swann 06'

"Individualism is absent when other peoples' standards, not reality and reason, are ones primary guide."

Yep, they're contrails- yes, they're always there,

You're seeing the shipping lanes of the sky- just like the Delaware River and Bay have marked shipping lanes, the sky above has marked flight lanes that stretch across the USA.

Also, all planes can make contrails- they're just a result of turbulence from the plane and cold air high up. So, most of the contrails you'll see are from higher fling passenger jets, with turbo jet engines, or perhaps turbo props- Small propeller driven planes don't usually fly high enough to form contrails-but some of big planes could - like the large WWII era B17s over Germany,



or the B-29s over Japan.


Since it's been so cold, and there's such a bright sky, you'll see the contrails more clearly, especially if you're up on the high hills near the suburbs- you can see the sky's filled with contrails from commercial aviation


You might also have seen some USAF planes patrolling Phillly because the president was here, most likely they would have been A-10 Warthogs from Willow Grove, - I do recall seeing a few F-16s over Philly in the months immediately after 9-11, but those are fast, high flying air superiority fighters- they're not built to loiter and patrol- which is what
A-10s would be doing while the President was in town. They might also have added the A-10 patrols back around Limerick Nuclear Plant since the drunken Piper Cub pilot buzzed the place- he's damn lucky they didn't shoot him down.

Hal

my inside sources say that contrails should disappear realtively quickly and that these trails are around for hours. is this true?

Well, contrails are basically clouds- I don't see why clouds should have to dissapear quickly . . .

I think part of that is determined by whether the source is a wake-
like the old fashioned propellers that mainly cause turbulence,

or whether the source is a jet where you have turbulence plus lots of heat.

Think of the difference between a can of soda that's shaken up and then "settles down" quickly, compared to a can of soda that's sitting on the stove, heated up and shaken up- the heated and shaken will take longer to cool

The jet should have both more turbulence and more heat - although jet exhaust cools quickly, the point is that water vapor acts differently than small water droplets.

It's rather like the difference between the visible exhaust of a car that's still warming up - water droplets, versus the mostly invisible water vapor of a car that's warmed up.


If you're ever at the Lansdale Exit of 476 around dusk, you'll see an bunch of interwoven contrails as you look west- the sun hits the main long distance flight routes, often you'll see 9 or 10 or more contrails in one section of the sky, low level local hops, mid level city to city traffic, and high level NE Corridor traffic all stacked one above the other.

Hal