ice halos and other optics

Diamond dust halo display initiated by a snow blower

This diamond dust display occurred on 1 April 1998 in Resolute Bay, Canada. The images have been scanned from slides which is why the display has lost its brilliance. But it was not the most brilliant display anyway. What’s more interesting here is how it formed. In two photos there is an ice cloud erupting from the Resolute Bay airport. It was caused by a snow blower attached to a tractor that was operating for two hours or so. Most of the snow it blew in the air fell immediately back to the ground, but there also came a cloud of invisible tiny ice particles that started drifting with the wind. These particles acted as a template around which the ice crystals that caused the halo display grew. This happens when air water vapor content exceeds ice saturation, only then can water vapor deposit on these ice nuclei. If the air moisture was below ice saturation, then there would not have been any ice crystal cloud that we see in the photos – and no halos either.

In some of the photos there is rudimentary Moilanen arc, which is not a surprise, since this was a man made display. The photos are in chronological order. As I was running away from the airport the display got constantly better because the crystals had time to grow bigger. After some time Resolute weather station caretaker Wayne Davidson drove by and took me further away from the airport where the display was better defined, though not any brighter, as is seen in the last image.

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