COPY
UNITED STATES DEPARTMENT OF COMMERCE
WEATHER BUREAU
Report
Information on "Ball Lightning"
I. Origin
Various theories and suggestions have been proposed to explain ball lightning, most of them being without well-established physical foundation. There is still doubt in scientific circles regarding the origin of a number of reported cases of ball lightning.
Briefly, the explanations of the origin of ball lightning may be broken down as follows:
(1) Brush discharge (St. Elmo's fire).
(May be stationary over sharp-pointed objects, or moving along or near the surface of wires, roofs, rocks, etc., especially on mountains. Conditions most favorable for brush discharge occur during thunderstorms, but the phenomenon may occur even during clear, dry, dusty weather. When a lightning stroke is approaching an object, the brush discharge becomes especially intense.)
(2) Intensely ionized, incandescent volume of air forming end of lightning stroke and lasting for short interval of time.
(This would occur mainly during thunderstorms following the passage of a lightning stroke. At the ground end, the terminal flash is intense, and vapors, smoke or molten material from objects fused at points struck may enhance and extend the duration of incandescence. After-image formed on the retinas of the eyes of a person looking at the brilliant flash at the point of discharge may give spurious effects.)
(3) Brush discharge in air containing high concentration of dust or other aerosols, during thunderstorms.
(If this occurs, it probably is associated with the path taken by a real lightning stroke, and presumably involves corona discharges from suspended particles and possibly combustion in some cases.)