[X1. July 2, 1970, Ann Arbor, Michigan
. While observing a thundercloud. "At and just above the peak of the storm cell the cloud mass seemed to be undergoing sudden changes in brightness lasting for several seconds at a time…. The phenomenon continued to occur repeatedly at intervals of 30-60 s during the next 15 or 20 min, providing the basis for the following description. The sudden brightening effect began
concurrently with lightning strokes in the main cloud mass, but continued after the lightning flash was over. It had the appearance of a ripple-like upward and outward spread of radiance from the region just west of the peak of the cumulus cloud, resembling somewhat a fan-like display of aurora borealis. It lasted a substantial fraction of a second with each lightning stroke. On one or two occasions it had the appearance of a bright ring moving rapidly outward and upward above the cumulus peak. On these occasions it was clearly observed to extend beyond the cloud and into the blue sky. A linear shadow, apparently cast by one of the cumulus masses, appared to shift its position suddenly up or down with each occurence of the event."
X2. August 18, 1950. St. Albans, England
. "At 12.25 GMT a cumulo-nimbus of moderate size was passing about four miles to the south, and giving rumbles of thunder about once every minute. While observing the cloud my attention was drawn to a bright streamer, apparently of cloud, projecting northwards from the anvil top for a distance of five degrees. As I watched, the streamer suddenly ‘exploded’ into a rapidly widening circle of light, fading as it did so. Immediately afterwards the streamer started to reform in the same place as before, only to repeat its ‘disappearing’ act again after a minute or so, presumably whenever an electrical discharge took place. On some occasions the streamer shifted violently to one side, changing its form greatly, but always returning to one spot. The spectacle lasted for half an hour, becoming fainter as the cloud moved away eastward."
X3. April 30, 1885. Denison, Texas.
A glowing region repeatedly travels along the tops of thunderclouds that were arranged in a long bank.
R1. Gall, John C., jun., and Graves, Maurice E.; "Possible Newly Recognized Meteorological Phenomenon Called Crown Flash
," Nature, 229:185, 1971. (X1)
R2. Hale, R.B.; "Unusual Lightning," Weather, 5:394, 1950. (X2)
R3. "Electrical Phenomena," Monthly Weather Review, 13:103, 1885. (X3)]