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From: Mika Sillanpaa (masillan_at_hidden_email_address.net)
Date: 10/25/1996



 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 were 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