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I've been following the debate on the elliptical halos and Bottlinger
rings,
and feel that I should have to make some comments on the subject too.
I was co-author with Traenkle in the paper of elliptical halos and
Bottlinger
rings. The connection of Ac virga and elliptical halos was obtained from
the
elliptical halo observations the network has made. The precence of
altocumulus was mentioned in almost all of the observations we had that
time.
Also the few photographed displays showed the connection to Ac.
True, there were some isolated reports of elliptical halos seen in
connection
of Sc or industrial plant plume or high clouds. Now as we have much more
photoes on elliptical halos, Marko Pekkola points out that in addition to
Ac
virga they are also often formed in Cc virga. Ac and Cc clouds are
somewhat
similar looking clouds and for a person who is not trained in identifying
the
cloud types they can be easily mixed together. So it is possible that also
in
earlier reports elliptical halos the Cc could have been misidentified as
Ac.
About the display of 14.2.88. In the report of Hakumaki Altocumulus is
mentioned to have occured at the time the ellipse was observed. The
altocumulus also showed a hint of iridescence - a very typical feature in
many
elliptical halo observations. So I think that the chance that Ac
virgaproduced
this display can't be totally excluded.
One comment on the nucleation and growing time of ice crystals. Last
January
in Fairbanks, Alaska, we (Walt Tape, Marko Pekkola, Jarmo Moilanen and I)
observed several halodisplays caused by huge power plant plumes. One
halodisplay showed up just few hundreds meters from the plant and we were
right below the plume from where the crystals fell down. The ice crystals
must
have nucleated and grown quite rapidly.
Even though I've been a co-author in paper that assumes the elliptical
halos
formed by multiple scattering, I don't trust that theory anymore. The new
photographs from Piikki show clear coloring in elliptical halos, which
multiple scattering can not explain.
Marko Riikonen
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