Sunday, March 26, 2006

Elliptical halo in Helsinki

Elliptical halo appeared in the skies today on 26. March 2006. This was one of those rare long lasting displays, with almost an hour duration. The image here shows some of the stacked photos of the display. All together I took more than 600 shots.

The formation of elliptical halos is still somewhat mysterious. While good simulations are produced by obtuse hexagonal pyramid crystals having pyramid apex angles of around 175°, the current knowledge of ice physics does not give much support for such a crystal.

The display was formed - as usual - in Altocumulus virga. More on the cloud associations here.


Blogger Michael Ellestad said...

Thats unusual marko for elliptical halo to last that long. The second one I got in 2005 lasted 15 to 20 minutes and only one ellipse was present but your display looks like two ellipses fused into one or is that from photo stacking?

27 March, 2006  
Blogger marko riikonen said...

That's not due to stacking. Actually, stacking had sharpened the arcs - compare to the originals shown at the site.

Sure there can be fusing. It also seems that there is a bit size variation, especially the upper part distance from the sun seems different in some photos.

27 March, 2006  
Blogger marko riikonen said...

Yeah, I was thinking that name of out site will lure also some of you Halo guys.

02 April, 2006  

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