Free Halo Simulation Program
© Jukka Ruoskanen 2010
Rovaniemi, 7/8th December 2008
Photo by Marko Riikonen *
Using a spotlight in diamond dust near ski resorts can be an astounding experience and at the same time scientifically fruitful as well. When a spotlight beam is cast into a diamond dust cloud one can see halo displays that bear a resemblance to simulations like no other display, except the most magnificient ones at South Pole.
Marko Riikonen photographed several new halo phenomena using this technique in Rovaniemi during two consecutive winters (2007-2009). This photograph is one of the premium catches including two previously undocumented haloforms: sub-120° parhelia and sub-Kern arc. The sub-halos in this photo are above the horizon; the light is downhill behind photographer's back.
Even if the spotlight beam is narrow and the light is positioned 100 meters away from the observer, the light hitting the crystals can not be considered parallel, but we are rather dealing with a divergent light situation. However, the parallel light approximation is justifiable for most situations. Therefore the simulation on the right is, of course, a parallel light simulation.
Only one plate crystal population was used to simulate the display. Plates were thick, 68% of them having aspect ratio in the interval 0.1 - 0.7. Additionally, the profile was allowed to vary within small limits. Is the sub-Kern too strong? Would you rather go with thinner plates? And what about different profiles? Go ahead and fine tune the simulation. The parameter file can be downloaded HERE.
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