Ice Crystal Halos

Simulations on the possible new arc from Moilanen crystals

Simulations on the possible new arc from Moilanen crystals

Here are some simulations to follow up with the possible new arc from Moilanen crystals ( 1 ). As suggested by Marko, I did some “photo quality” simulations with the two Moilanen arcs using Jukka Ruoskanen software. The Moilanen crystals are simulated using 34deg prisms pointing up.
First I simulated Jari Luomanen’s picture ( 2 ) which shows best the two arcs. I found that two Moilanen population tumbling with 1° and 14° deviation matched well the display.

Then I tried to compare two low source elevation displays from Marko Riikonen ( 34 ),and Milan Osecky ( 56 ). I simulated them with the same populations as the one I found from Jari Luomanen picture (1deg and 14deg standard deviation tumbling angle). The differences between the two populations are pretty subtle at this low source elevation. They are mostly in the shape of the outer edge of the Moilanen arc and in aspect which can be either hollow or solid. New arc has a more solid and curved edge. Although it is difficult to know for sure, I think the two pictures show the two different arcs.

Finally, I did some simulations that shows how one arc becomes another when the tumbling angles are increased, and for different source elevations ( 78910 ). The limit between the two arcs would be somewhere between 8 and 16deg tumbling angles. The amount of crystals is kept constant in the simulations so brigthness can be compared. The two arcs vanish quickly when source elevation is increased. With the tumbling angles used (up to 64deg standard deviation), no lower component appears for the new arc.

Nicolas Lefaudeux


  • Excellent! It looks like you got it right with Luomanen photo: the new halo is explained concerning the orientation and wedge angle. This will give new spice for the next diamond dust season games, we will be looking especially carefully when moon is high.

    Also, good simulations. You managed to create there nice sky illumination. That’s already Avatar quality.

  • Avatar!? I love that movie at one point when jake sull is up in the floating mtns of plante Pandora you can see a rainbow in the waterfall.

  • Yes, Nicolas, the explanation of the feature in Luomanen’s photo seems believable, since no modification of the wedge angle was needed. Good job!

  • thanks! actually there seems to be a sort of “window of opportunity” for this arc to be identified easily.

    for source elevation lower than 15deg, the arc is very close to usual Moilanen. the identification is pretty difficult being only based on the shape an aspect of the arc which is pretty similar to usual Moilanen. this is what I tried to show with the two low source displays simulations.

    For source elevation higher than 30deg, the arc vanishes for tumbling angles of 14deg (similar to the one I found to simulate Jari’s picture).

    but maybe larger tumbling angles are possible so arc appears at higher source elevation too. time will tell


Leave a Reply

Your email address will not be published. Required fields are marked *