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> It seems to me that the discussin of impurities causing wild
> colors in noctilucents relates also to the two photographs
> I now have showing circumhorizontal arcs generated in jet
> exhaust contrails. This ribanding of spectral color was
> imparted to the contrail but not to the surrounding clouds.
> Is this what we are talking about, or am I off base?
I am afraid you mixed discussions. If I have correctly
understood, there was discussion of green sky effect
related tornados and Timo Nousiainen give a suggestion
that inpurities in droplets could be one explanation
of green color.
When talking about "NLC" photograph in S+T June 1995
issue taken by Pekka Parviainen: This case is not
noctilucent clouds but a rocket exhaust.
In the article written you in May 1995 there were
circumhorizontal arc in a jet contrail. The meteorological
conditions in case were suitable to ice crystal formation in
contrail but not in other clouds around. They could be eg.
in the different altitude and different temperature etc.
Even in the same cloud layer type of ice crystal could
vary a much. Eg. yesterday I saw a bright sun dog in a
small cloud. There were lots of similar cirrus clouds
around the Sun, but no other halo forms were seen. It
seems, that only in some parts of clouds there were suitable
plate crystals to form a halo and when they were in the
correct direction a sundog was seen.
-Veikko-
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