Halos, Parhelic Circles and Parhelia (Sun Dogs) sometimes occur in high altitude cold temperature Cirrostratus cloud when ice crystals of particular types are thinly and evenly dispersed, most commonly ahead of an approaching cold front. They can also occur in low level mist conditions and appear to float in the air only metres away with objects such as trees and ridges in the background and beyond.

'Parhelia or Sundogs are generated by plate-shaped hexagonal ice prisms (crystals). When falling undisturbed, the plates automaticaly orientate horizontaly. The sunlight enters one face of the prism and exits the next one'. www.meteoros.de.

Links to more Atmospheric Phenomena web sites:

Arbeitskreis Meteore e.V. (Atmospheric Phenomena) - http://www.meteoros.de/index.htm

Atmospheric Optics - http://www.atoptics.co.uk/

The Great South Pole halo display on January 11, 1999. - http://www.usatoday.com/weather/resources/coldscience/acomsim1.htm