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Falcon
Joined: 04 Aug 2000
Posts: 87
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 Wed Oct 04, 2000 4:53 pm
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Come on Thermit give us a picture of that kind of trail (-- / --) that isn't just two airliners crossing flight paths.
I watched an aircraft today leaving small, regularly spaced trails. Why was this occuring?
Simple, mountain wave activity, caused in a stable airmass and characterised by the formation of lenticular clouds. As the air rises and falls across the affected area it's Relative Humidity changes, obviously once it reaches dew point temp it condenses out to form the lenticlar cloud. It, of course, also accounts for the evenly spaced formation of contrails. I know for a fact that nobody in that aircraft was spraying anything!
I have to admit to the untrained eye it would look a little strange. |
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Thermit
Joined: 08 Jul 2000
Posts: 3136
Location: Texas |
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Wed Oct 04, 2000 5:13 pm
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I'm talking about an area of the sky that was full of little contrail strips. Not long intersecting trails.
You and Seeker have both explained that there is a natural mechanism by which trails can appear as dashed lines. I can buy that, no problem. This could give a trail symbolically represented lke this:
-----..........-----..........-----.......-----
The dashes are the trail and the periods are the area with no trail.
The concept that you have both presented implies that there are no trails in the "........" area, because this area doesn't support contrail persistance.
But, I've seen a situation where more of these strips inhabited the "......." area. This is the part that doesn't fit, in this particular instance, the theory you guys are presenting.
Also, I would expect that the boundaries between the two air layers would be somewhat fuzzy. Even though the layers are seperated, it shouldn't be a razor sharp boundary. But the fresher strips that I saw had very sharp edges. Similar to this...
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Falcon
Joined: 04 Aug 2000
Posts: 87
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Thu Oct 05, 2000 12:38 am
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The crossing trail could easily be at a higher or lower level that does support contrail formation.
I am not talking about separate "air layers" as you describe them, this is not a frontal issue. I'm talking about the natural rise and fall of air in a stable airmass.
Also, it is a pretty sharp line between condensing at dewpoint and not condensing very slightly above dewpoint. An aircraft wing generating lift, and certainly an aircraft pulling enough G close to the cloudbase or in a nearly saturated airmass will generate condensation above the wing in the low pressure area or in the form of wingtip vortices.
Finally, the "sharp" edges of the trails in your pictures may simply indicate a lack of upper winds. |
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Thermit
Joined: 08 Jul 2000
Posts: 3136
Location: Texas |
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Sun Oct 15, 2000 4:12 pm
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By Deborah from Boston |
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Swedishoo
Joined: 09 Aug 2000
Posts: 429
Location: NC |
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Sun Oct 15, 2000 6:06 pm
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Oh MY!! That's a perfect shot of a cut off Deborah!! Air pockets or low pressure areas could not leave that little tail at the top. The other photo posted earlier also show this, but Deborah's close up is a great one.
I'd like to hear Falcon's comments on this image.
Christy |
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goldrush
Joined: 04 Sep 2000
Posts: 109
Location: No, Calif. USA |
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Sun Oct 15, 2000 7:48 pm
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An excerpt from my little old (1968) weather forcasting book.. "TRAILS formed by a aircraft help to tell wind speed and direction aloft. When they are dense they indicate the possible influence of a warm front. When they do not persist they indicate a relatively dry upper atmosphere and therefore little chance of major deterioration. High speed upper winds shred trails rapidly. If they shred sideways then the wind is across the trails, and in (3). If they form castellated tops then the wind is parallel to the trails." pg 12 Instant Weather Forcasting -- From pg 42 and picture titled "Quiet evening" ...the upper cloud is largely spread out vapor trails, but they are dense and persistent. There seems, however, to be no organised wind directon at their level and this points to a continuation of the present quiet weather. |
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Falcon
Joined: 04 Aug 2000
Posts: 87
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Mon Oct 16, 2000 11:59 pm
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OK then here are my comments.
Looks like the aircraft photographed is at the top of decent, throttling back will create a sudden change in engine output and will therefore obviously affect the formation of a contrail. As for the two "tails" on the contrail, they are nothing more than the remants of condensed wingtip vortices in the saturated air of the trail.
Either that or the crew have just turned the big "CHEMTRAIL" switch off! 
Incidently, can someone please tell me what an "air pocket" is. |
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cydoniaquest
Joined: 12 Aug 2000
Posts: 797
Location: nowhere |
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Wed Oct 25, 2000 4:33 am
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DELETED BY THE ARTIST FORMALLY KNOWN AS CYDONIAQUEST
[Edited 2 times, lastly by cydoniaquest on 01-13-2001] |
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Swedishoo
Joined: 09 Aug 2000
Posts: 429
Location: NC |
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Wed Oct 25, 2000 5:04 am
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hehehehe, Cy
You have to admit, you laughed too Falcon. Funny stuff.
Christy |
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goldrush
Joined: 04 Sep 2000
Posts: 109
Location: No, Calif. USA |
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Wed Oct 25, 2000 5:12 am
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I have watched many contrails dissipate in various fashions. The trouble with a photograph is that it only depicts one point in time. It is unfortunate that many pictures of contrails do not include the aircraft or time lapsed, since the contrail was produced and also including weather conditions before, during and after, as well as time of day, or date and geographical orientation. I can understand the curiosity that is generated by such photos. A huge amount of supporting or dismissing information is lacking. Usually, I have seen these kinds of contrails over hills and mountains, in the morning. To me, it is not evidence of spraying. |
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elvis lives
Joined: 30 Sep 2000
Posts: 143
Location: Pismo Beach, California |
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Wed Oct 25, 2000 5:39 am
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Mountains out of mole hills.....
Great shots of contrails folks, that’s all they are. I have seen many, many, many contrails that break up like those pictured. That is a normal occurrence in the skies.
Your sprayer on, sprayer off logic is wishful thinking. Tell me 1 reason (just 1 will work) why a pilot would turn his sprayers on and off every few hundred feet? And PLEASE don't say his spray tanks were near empty..........
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elvis lives
Joined: 30 Sep 2000
Posts: 143
Location: Pismo Beach, California |
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Wed Oct 25, 2000 5:54 am
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Deborah...
The contrail in your picture is not broken. If you look to the top right, you will see that the contrial continues through the end of the photo. The last part of the contrail is darker than the rest of the contrail because of reflection from the sun. |
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Falcon
Joined: 04 Aug 2000
Posts: 87
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Wed Oct 25, 2000 2:15 pm
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Hmmm, almost more non believers than believers now. No surprise there then!
Cy, nice definitions. You really are a nice person aren't you. |
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