Free Halo Simulation Program
© Jukka Ruoskanen 2010
Churanov, 5th January 2010
Photo by Roman Szpuk *
Extremely bright diamond dust parhelia are a warning sign for the only secondary halo observed so far, the 44° parhelia. Multiple scattering halos are a theoretically understood group of halos. First solid evidence of it came from the famous 1970 Saskatoon display, and lately the 44° parhelia have been observed yearly.
For multiple scattering halos to arise the light has to meet at least two crystals on its way from the light source to the observer's eye. Most of the light is still deviated only by one crystal.
How often does light meet two or more crystals? Is it possible to model the ice crystal layer so that the scattering outcome is close to what we can see in the sky? HaloPoint 2.0 has an algorithm that is trying to answer these questions.
On the right is a simulation - photograph pair of a diamond dust display photographed by Roman Szpuk in January 2010. The simulation was done using two ice crystal populations: oriented plates (tilt 6°) and almost randomly oriented equidimensional (aspect ratio about 1) crystals (plate tilt 60°). The ice crystal layer height (for both populations) was 25 meters from the ground and observer's eye was 2 meters from the ground. The density of the random population was such, that its mean free path was 500 meters and similarly for plate crystals the mean free path was 220 meters. With these settings the simulation agrees well with the photograph.
The effect of mean free path versus the observers height in a plate crystal layer having height of 100 meters is illustrated in this webpage (beware: there is a matrix of 100 simulation images, about 50 kB each, altogether a bit less than 5 MB of data). It is interesting to see how the mean free path affects the visibility of the halos. The parameter file of the simulation above can be downloaded HERE.
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