A halo phenomenon produced by reflection of sunlight on ice crystals in clouds. It can be seen from aircraft or mountains and looks like a brilliant white spot on the clouds below the sun. Found on http://www.bbc.co.uk/weather/weatherwise/glossary/u.shtml
A halo phenomenon produced by reflection of sunlight on ice crystals in clouds. It can be seen from aircraft or mountains and looks like a brilliant white spot on the clouds below the sun.