Bedankt voor de link, Ben.
Klinkt inderdaad aannemelijker.
Harald Edens: "In some cases a distrail may transform into a cloud hole: a large elliptical hole in altocumulus with virga in the middle."
Al zoekend op de term 'distrails' vond ik ook de volgende herldere uitleg:
"The picture you sent contains a contrail, an altostratus cloud, and the
so-called "vortex" cloud. The "vortex" cloud is an example of glaciation.
That is, a thin, supercooled liquid water cloud (the altostratus in this
case) is rapidly converted to an ice crystal cloud. A supercooled liquid
water cloud is any cloud composed of water droplets with temperatures below
freezing. They can exist at temperatures, T, between 0 C and -40C. All
droplets turn immediately to ice when T < -40C.
The reason supercooled clouds exist is that there are no nucleating agents
available in the vicinity to allow the phase transformation to take place
when T = 0C. When a thick supercooled cloud is present, icing conditions
are also likely because the plane flies into the cloud and serves as an a
big ice nucleus. Supercooled clouds are most likely to be found in pretty
clean air.
If you have a thin supercooled cloud like the one in your picture, the
plane will not ice up because there is not enough water available and the
drops are usually so small they get pushed out of the way. However, the
exhaust from the plane has both water vapor and nucleating aerosols. Thus,
the conditions are right for changing the phase from water to ice. So,
when the plane flies through it, the exhaust causes the droplets to rapidly
change into ice. As soon as that happens, the newly formed ice crystals
start to grow very quickly and become too large to be suspended by the
ambient wind. Therefore, they fall out in the form of precipitation as you
see in the "vortex". This ice versus water thing is something I have
discussed many times before in the talk about contrails. The likely reason
from the circular area is that the plane was ascending or descending and
briefly passed through the cloud in or near the center of the circle. The
falling ice crystals depleted the moisture in the area around the center of
the circle producing the clear ring around the fall streak.
At the higher altitude, the aircraft must have run into some colder moist
air that produced the contrail. If the plane actually flies just below or
in the thin altostratus or altocumulus cloud, the result of the glaciation
will be a distrail. This vortex cloud is simply a discrete version of the distrail."
(Bron: http://www.chemtrailcentral.com/ubb/Forum20/HTML/000036.html)
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