Utah Moilanen Arc ~ Troy Kapinos captured these blindingly bright halos over Park City, Utah on the morning of 15th January ’15. See the key below for halo identification.

All images ©Troy Kapinos, shown with permission
A ski resort is nearby. Many ski-slope snow blowers spray out bacteria to nucleate their snow crystals. The snow falls directly onto the slopes but some bacteria nuclei get carried far downwind where they are very effective in also promoting the gradual growth of the small hexagonal prisms that produce halos. These crystals are almost perfect and so produce bright and often very rare arcs. The displays can rival the very best of Antarctic halos. The crystals helped in their growth by enzyme nucleation are still natural and the halos still stupendous!

The upper tangent arc rivals the sun and signals that the air is full of horizontal column crystals. these also generate the outer colourful supralateral and infralateral arcs. They also produced the amazingly prominent Wegener arc.

Some Parry crystals were about too. The upper Parry arc is almost lost in the glare of the tangent arc but the helic arcs coursing from the sun reveal the crystals' presence.

Randomly oriented crystals of some sort made the 22° halo and the and traces of the 46°.

Mystery crystals give a bright and almost complete Moilanen arc between the sun and the upper tangent.
We have still not explained its origin.

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