Crown flash is a rarely observed meteorological phenomenon caused by the effect of atmospheric electrical fluctuations on the alignment of ice crystals.
[1] The current hypothesis for why the phenomenon occurs is that sunlight is reflecting off, or refracting through, tiny ice crystals above the crown of a cumulonimbus cloud.
When the electric field is disturbed by electrical charging or discharging (typically, from lightning) within the cloud, the ice crystals are re-oriented causing the light pattern to shift in a characteristic manner, at times very rapidly and appearing to 'dance' in a strikingly mechanical fashion.
Unlike sundogs, however (which are also caused by refraction of sunlight through ice crystals), these features move and realign within seconds, forming beams and loops of light, and the effect appears localised directly above the cloud rather than at some distance to the side(s) of the sun.
The first scientific description of the crown flash phenomenon appears to be in the journal Monthly Weather Review in 1885,[4] according to the Guinness Book of Records.