Free Halo Simulation Program
© Jukka Ruoskanen 2010
Fairbanks, 31st Dec 2009
Photo by Walt Tape *
New year's eve at Fairbanks was full of halo party - Walt Tape watched a great lunar odd radius display all the way until morning light. The 23° upper plate arc is unlike in any other photograph before as well as the helic arc, probably arising from pyramidal face reflections.
The starting point for simulation efforts is the 23° plate arc. It is almost perfect in shape, indicating rather small tilts for the truncated pyramids. While the 23° plate arc tolerates quite large tilts before its shape starts to severly break up, the pyramidal helic arc, on the other hand, is sensitive to tilting angle and thus gives us a tool for tilting angle estimation in this display. One finds, that tilts larger than 3° or 4° decrease the visibility of the pyramidal helic arc too much. With a tilt of 3° the 23° plate arc looks also consistent with the photograph.
One population isn't enough to explain all halos in the photograph. It seems that as many as four populations are needed, which may be preposterous. For example, the random population (popu 3), which with that crystal is far fetched, had to be introduced to get the 23° halo complete same time avoiding other rings.
Population 2 was needed to bring in the strong 18° plate arcs. But as usual, the 18° plate arcs are annoyingly well defined, which is highly inconsistent with the photo. One fix could be an increase of tilt, but at the same time that causes the 20° halo at the top to intensify, and we do not want that.
There are numerous other problems in the simulation as well. Can you get a closer match? The parameter file of the simulation above can be downloaded HERE.
[*]