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Posted: Wed Dec 20, 2006 8:42 pm Post Subject: Contrail fragments?
What are these short cloud fragments?
They were photographed with a cellphone camera from Silverstream r/w station, at 8:37am on Monday 18 Dec 2006.
The view is due north and the cirrus was moving approximately towards the southeast, and moving fairly quickly. These directions differ from those in the caption for this image in the gallery. I uploaded the iamge before I had looked at a map - my bad.
The sun is high in the sky and about 45 degrees to the right of the view direction.
I suggest that these are contrail fragments origionally formed on one of the
flight vectors north or northeast from Wellington, and then have been carried southeast by the wind while remaining more or less parallel to the flight vector. They don't look fresh and the ones further southeast are
less distinct and were dissipating.
It is possible that there were no contrails formed at the time the planes traversed the area, but these fragments formed later in acsending (and cooling) air that already had relatively higher Relative Humidity. The sky to the north was full of cirrus (high RH) while it was clear over Hutt Valley and Wellington (lower RH).
I think the planes exhausted the water vapour in the narrow zone along the flight path. This water vapour didn't condense immediately, but later when the ambient temperature lowered to below the dew/frost point.
This is more or less how cirrus clouds (or any clouds) form, and jet engine exhaust is water vapour (and other combustion products), after all.
Streamers of ice particles can also be seen in the upper centre part of the image. I reckon that the contrail fragments are at about the altitude of the top of the ice crystal streamers.
I wouldn't call it "activity", Deano. It might be unusual, but not unexplainable.
I nearly posted it in "Cloud Appreciation", but since there's a forum for contrails and such, I posted it under "Discussion". I didn't intend it as a "Report" of anything of importance.
It's a good example of contails drifting southeast in the wind, possibly off the H499 flight vector running north from Wellington. There are examples of it all the time; it is seldom calm up there. Contrails don't stay exactly where put, as observed but not recognised elsewhere.
