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Dear Halo Enthusiasts!
Having seen quite an amount of displays of elliptical halos this
year, I would like to participate in the debate with a few comments. My
views are based on empirical experience and discussions with e.g. Mr.
Riikonen.
First, elliptical halos are NOT as rare as previously thought. My work in
the
summer as a cemetery gardener gave me an excellent opportunity to follow
celestial happenings. I would like to state that I saw almost every halo
display last summer, six of those contained one or more ellipticals. On
the contrary, I'm not sure if I saw parhelic circle, for example, as often
as ellipses...Interesting because there has to be very few displays I have
missed. There was always Ac/ Cc cloud in the sky when ellipses were
present - usually whole the sky was covered with Ac/Cc in varying shapes,
not always, but often, lenticularis. The ellipses were probably caused by
virga from those clouds - though, only once there was a clear,
"traditional" virga visible.
Consequently, the crystals causing elliptical halos has to occur
abundantly enough to give rise to the bright halos as frequently as those
causing parhelic circles. The "elliptical crystals" cannot be rarities in
nature, and they're connected with large areas of Ac/Cc, especially "wave
clouds" - still, usually NOT as a homogeneous population.
My opinion of the origin of ellipses has turned against multiple
scattering. Still, has there to be any physical connection between
ellipticals around the sun and Bottlingers?! An obvious assumption is that
of course, and it's easily explained by means of both multiple scattering
and pyramids. But it would be highly prejudiced, however, to exclude
gyration as an origin to Bottlingers if multiple scattering is excluded. I
don't know if gyration is a possible falling mode for ice-crystal-size
particles, but I guess - because of large differences in Reynolds numbers
- model experiments with bodies of centimeters large may give somewhat
inapplicable results.
Why is the pyramidal theory better? A few points:
-white, single ellipses vs. multiple, colored ones
The best display of the year ( in July) begun with two colored, extremely
sharp ellipses which gradually, in front of my eyes, evolved into a
single, diffuse, white ellipse: tilting angles or variations in refracting
angles increased or crystal size decreased. So, white ellipses are just
superpositions of larger number of pyramidal-originated, colored
ellipses.
-polarization
when I finally remembered to check the polarization when an ellipse was in
the sky (the last display) the result was clear: The polarization vector
was just opposite to that predicted by multiple scattering. I have also
photos trough polarization filter, they're still in my camera.
I'm convinced the displays(for example those I saw last summer) cannot be
explained with a fixed pyramidal angle. This is a defect, but not a very
serious one: I remember having heard from Mr. Riikonen that Mr. Tape has
investigated possible pyramidal angles in the range of a couple of
degrees. The results is that there are a huge number of possible angles.
Some of them might be more probable under some conditions.
An interesting feature is the fact that no "random halos" from
"elliptical pyramids" have been reported. This can be interpreted either
by abandoning those strange pyramids, i.e. they don't exist. But another
thing that comes to my mind is that pyramidal angles of a couple of
degrees
are always associated with crystals that do orient.
Regards,
Mika Sillanpaa
Mirjankuja 4 C 18
02230 Espoo, Finland
masillan_at_cc.hut.fi
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