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Crown flash

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Crown flash is a rarely observed meteorological phenomenon caused by the effect of atmospheric electrical fluctuations on the alignment of ice crystals. It has been described as "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 electric field effects around the cloud,[2] so the effect may appear as a tall (sometimes curved) streamer, pillar of light, or resemble a massive flash of a searchlight/flashlight beam. 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.[3] The effect may also sometimes be known as a "leaping sundog". As with sundogs, observation of the effect is dependent upon the observer's position – it is not a self-generated light such as seen in a lightning strike or aurora, but rather a changing reflection or refraction of the sunlight. Unlike sundogs, however (which are also caused by refraction of sunlight through ice crystals), the crown flash effect appears localised directly above the cloud.

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 uncommon and not well documented. Starting with an initial video upload in 2009 dozens of YouTube videos have since been emerging 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 (5281): 184–185. Bibcode:1971Natur.229..184G. doi:10.1038/229184b0. PMID 16059137. S2CID 4260434.
  8. ^ "YouTube Playlist of Crown Flashes by upload date". Retrieved 2018-08-28 – via YouTube.
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