Thursday, 8 October 2009

Asymmetric intensity of 22° halo on ice surface

This 22° halo on ice surface was seen on 17 January in Tampere. It was more pronounced on the right side. Intensity asymmetry was not caused by local changes in crystal densities because it was seen wherever I walked on the ice.

The effect must be made by atsimuthally oriented crystals on the lake ice. Possibly wind blowing from one direction had caused non-uniform deposition of moisture, resulting in (poorly) atsimuthally locked crystals.

See animation ( 1 ), which involves about 70 photos taken during 30 meters camera movement. The asymmetry effect is also seen in stacked image of 117 frames ( 2 )

This is not the first time when asymmetry of halos on ice surface has been noticed. In December 2007 Jari Piikki photographed curiously inclined halos in Juva ( 3 ).


  1. This is intriguing case indeed. You have documented it well. Some coherent alignment of crystals on the surface is surely needed to explain the intensity difference between the two branches of 22 halo.

    By the way, I have already spotted my first surface halo this season. Last weekend it was cold enough so that all vegetation was filled with crystals. A nice 22 halo followed me on the grass when I was bicycling in the morning. The halo was not good when I was standing still, but the movement made it look good.

  2. Yes, this interesting case is really well documented, indeed. I find the animation especially good.

    So it seems, the winter season has arrived in Finland, Jukka.

  3. Not so well documented. I did not succeed in photographing the crystals on the ice. All photos came blurry.