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[den]

Comments

Re:

[level-head.livejournal.com]

Well, not quite. Certainly the wing tip vortices can generate these clouds, though this is generally a low altitude, high humidity phenomenon. You'll often see this from inside the aircraft when landing on a humid day, over the wing and off the tip. Just before landing, the aircraft is in its "dirtiest" configuration, and the wing loading is highest, causing the pressure differential you describe. But at high altitude, the story is very different.

The the soot particles in jet exhaust give the water vapor something to form on, which is in rare supply in the high troposphere. Also, the water vapor itself is coming from the jet exhaust -- it is a significant product of combustion.

No, of course it's not dangerous -- but a four engine jet such as a 747 leaves a different contrail shape from twin such as a 757 or 767, and you can often make out the individual engine trails before they merge. It's not from the wings (though the shape is very much influenced by the after effect of airflow over the wings).

Some studies show a very small climate change caused by the contrails themselves.

===|==============/ Level Head

[acelightning.livejournal.com]

Re:

[level-head.livejournal.com]

The high altitude phenomena that Batty pictured, and that I was describing, are called both "contrails" and "vapor trails" -- the literature does not distinguish one of these as the low altitude effect of heavy wing loading on humid air near the dew point.

That's an interesting process to watch, and very pleasant -- but the resulting clouds are not long lasting.

The contrails/vapor trails that cross the sky at altitude are exhaust-driven (and airflow-shaped) from everything that I have observed and read on the topic.

===|==============/ Level Head

[acelightning.livejournal.com]

[dewhitton.livejournal.com]

You can see the exhaust trail forming in a 747 if you go to the last window and look back. I could see the first fingers of condensation around the outside of the stream chasing the plane.

[acelightning.livejournal.com]

[kelloggs2066.livejournal.com]

I recall seeing a lot of paintings of the contrails coming off the engines of B-17s. There are undoubtedly wingtip vortex created contrails, but they're much smaller than the engine particle created contrails. I would guess that the atmospheric conditions which allow them to form is probably farther from the norm than the engine contrails.

Scott (Not a meteorologist) Kellogg

[level-head.livejournal.com]

If you see pictures of aircraft at altitude -- and we have a number of military aircraft pictures floating around now due to recent activity -- you can see that these are indeed exhaust-triggered rather than wake vortices.

As a general rule, the faster the aircraft is flying, the less severe the wing vortices are. The FAA is only really concerned about them when the heavy aircraft are low and slow, briefly after takeoff and for some time on final approach.

There is always some tip votice activity -- you may have seen a number of recent aircraft with "winglets" on the ends of the wings to squeeze a bit more out of this wasted energy -- but it is less dramatic, has a slower rotational speed, and stays around for a shorter period of time at cruise altitude.

It is possible to get "squeeze clouds" at altitude, but the conditions that support it are much more rare. Contrails, however, are very common.

===|==============/ Level Head

[kelloggs2066.livejournal.com]

Ooo!

Wonderful Book! :D

Scott