Crown flash

Crown flash is a rarely observed weather phenomenon involving "The brightening of a thunderhead crown followed by the appearance of aurora-like streamers emanating into the clear atmosphere".[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. These ice crystals are aligned by the strong electro-magnetic effects around the cloud,[2] so the effect may appear as a tall streamer, pillar of light, or resemble a massive flash of a searchlight / flashlight beam through the clouds. When the electro-magnetic field is disturbed by electrical charging or discharging (typically, lightning flashes) within the cloud, the ice crystals are re-orientated causing the light pattern to shift, at times very rapidly and appearing to 'dance' in a strikingly mechanical fashion.[3] The effect may also sometimes be known as a "leaping sundog". As with sundogs, the observer would have to be in a specific position to see the effect, which is not a self-generated light such as seen in a lightning strike or aurora, but rather a changing reflection/refraction of the sunlight.

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[5]. Also mentioned in Nature in 1971[6] and in a letter to Nature slightly earlier in the same year,[7] this phenomenon is regarded as rare and not well documented. Starting in 2009 several YouTube videos have since emerged that appear to document this phenomenon.[8]

See also

References
  1. Corliss, William (1982). Lightning, Auroras, Nocturnal Lights, and Related Luminous Phenomena: A Catalog of Geophysical Anomalies. ISBN 978-0915554096.
  2. Vonnegut, B (1965). "Orientation of Ice Crystals in the electric field of a Thunderstorm". Weather. 20 (10): 310–312. Bibcode:1965Wthr...20..310V. doi:10.1002/j.1477-8696.1965.tb02740.x.
  3. "A New Natural Phenomenon - Crown Flash". Retrieved 2015-09-03.
  4. "Electrical Phenomena". Monthly Weather Review. 13: 103. 1885. doi:10.1175/1520-0493(1885)13[100c:AE]2.0.CO;2.
  5. "Guinness Book of Records - First description of a crown flash". Retrieved 2019-05-26.
  6. Graves, Maurice E.; Gall, John C.; Vonnegut, Bernard (1971). "Meteorological Phenomenon called Crown Flash". Nature. 231 (5300): 258. Bibcode:1971Natur.231Q.258G. doi:10.1038/231258a0. PMID 16062656.
  7. Graves, Maurice E; Gall, John C (1971). "Possible Newly Recognized Meteorological Phenomenon called Crown Flash". Nature. 229: 184–185. Bibcode:1971Natur.229..184G. doi:10.1038/229184b0. PMID 16059137.
  8. "YouTube Playlist of Crown Flashes by upload date". Retrieved 2018-08-28.
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