Moilanen arc without snowguns

I was recently filing images digitized from somewhat older slides and came across this upper tangent arc image from many years ago, in the early morning from here in Calgary. I decided to subject this image to some processing, in particular, embossing the image in Photoshop and low and behold, a faint Moilanen arc showed up, as you see in this composite image!

I certainly do not live anywhere near to a ski slope or factory chimney that would produce lots of ice crystals. There is no evidence on the photo of local ice crystals as we see often in diamond-dust displays. The climate here is very dry and we often find low-lying layers of diamond dust particularly over our river.

Thus, I hesitate to claim that this is a "natural" Moilanen arc but it was not taken near to ski slopes. Maybe our furnaces produce the requisite crystals sometimes, in which case I will be on the lookout next winter for a repeat of this display.

Alan Clark

Odd-radii again

Alan Clark sent the above image, which shows the same display that Elmar Schmidt saw from Virginia, and which can be read about in the previous post. Alan photographed the halo from Dulles Airport, about 120 km NE of Elmar's site. The Sun elevation was about 58 degrees, and it was between 15:00 to 16:00 local summer time. As Alan says: "The display was not perhaps as clear as Elmar's in that some components of the odd halo were not distinct." ( 1 )

Alan has sent another pair of odd radius halo images. These were taken from Calgary, Alberta, Canada in May, 2009. ( 2 - 3 )