- - , Algemeen, , Michel T. Talbot, Ball Lightning, 1995; Ball lightning (boules de feu or foudre spherique; Kugeblitz) is the
name given to the mobile luminous spheres which have been observed
during thunderstorms. A typical ball lightning is about the size of an
orange or a grapefruit and has a lifetime of a few seconds. Compilations
of eye-witness reports of ball lightning have been published by
Brand(1923), Rodewald(1954), Dewan(1964), Silberg(1965), McNally(1966)
and Rayle(1967) among others. Visual sightings are often accompanied by
sound, odor, and permanent material damage, and hence it would appear
difficult to deny the reality of the phenomenon [as Humphreys(1936) has
done]. In a letter to the editor of the London Daily Mail, Morris(1936)
described an unusual incident in which a ball lightning caused a tub of
water to boil:
During a thunderstorm I saw a large, red hot ball come down from the
sky. It struck our house, cut the telephone wire, burnt the window
frame,and then buried itself in a tub of water which was underneath.
The water boiled for some minutes afterwards, but when it was cool
enough for me to search I could find nothing in it."
Photographs purported to be of ball lightning have been published by
Jensen(1933), Kuhn(1951), Wolf(1956), Davidov(1958), Jennings(1962), and
Muller-Hillebrand(1963). A phenomenon very similar to, if not identical
with, ball lightning has been reported to occur in submarines due to
discharge of a current about 150,000 amp direct current from a 260-volt
source across a circuit breaker(Silberg, 1962). In addition a number of
reports were received of ball-lightning-like phenomena being initiated
accidentally in high-power electrical equipment.
Ball lightning and St. Elmo's fire are sometimes confused. St. Elmo's
fire is a corona discharge from a pointed conducting object in a strong
electric field. Like ball lightning, St. Elmo's fire may assume a
spherical shape. Unlike ball lightning, St. Elmo's fire must remain
attached to a conductor, although it may exhibit some motion along the
conductor. Further, St. Elmo's fire can have a lifetime much greater
than the lifetime of the usual ball lightning.
From the many published ball lightning observations, it is possible to
compile a list of:
Ball Lightning Characteristics
- Occurrence
- Most observations of ball lightning are made during thunderstorm activity.
Most, but not all, of thunderstorm-related ball lightning appear almost
simultaneously with a cloud-to-ground lightning discharge. These ball
lightnings appear within a few meters of the ground. Sometimes ball
lightnings are reported to occur near the ground in the absence of a
lightning discharge. Ball lightnings have also been observed to hang
in mid-air far above the ground and have been observed falling from a
cloud towards the ground.
- Appearance
- Ball lightnings are generally spherical, although other shapes have been
reported they are usually 0.1-0.2m in diameter, with reported diameters
ranging from 0.01-1.00m. Ball lightnings come in various colors, the most
common colors being red, orange, and yellow. Ball lightning are generally
not exceptionally bright, but can be seen clearly in daylight. They are
usually reported to maintain a relatively constant brightness and size
during their lifetimes, although ball lightnings which change in
brightness and size are not uncommon.
- Lifetime
- Ball lightnings generally have a lifetime of less than 5 seconds.
A small fraction of reports indicate a lifetime of over a minute.
- Motion
- Ball lightning usually move horizontally at a velocity of a few meters
per second. They may also remain motionless in mid-air or may descend
from a cloud towards the ground. They do not often rise, as would be
the case if they were spheres of hot air at atmospheric pressure in the
presence of only a gravitational force. Many reports describe ball
lightning which appear to spin or rotate as they move. Ball lightnings
are sometimes reported to bounce off solid objects, typically the ground.
- Heat, sound and odor
- Rarely do observers of ball lightning report the sensation of heat.
However, accounts of ball lightning which burned barns and melted wires
do exist. One report found in McNally (1966) described a ball lightning
which hit a pond of water with a sound "as if putting a red hot piece of
iron into the water." Sometimes ball lightnings are reported to emit a
hissing sound. Many observers report a distinctive odor accompanying
ball lightning. The odor is usually described as sharp and repugnant,
resembling ozone, burning sulphur, or nitric oxide.
- Attraction to objects and enclosures
- Ball lightnings are often reported to be attracted to metallic objects
such as wire fences or telephone lines. When attached to metallic
objects, they generally move along those objects. Some or all these
observations may refer to a type of St. Elmo's fire. Ball lightnings
often enter houses through screens or chimneys. Sometimes they are
reported to enter houses through glass window panes. They are also
reported to originate within buildings, on occasion from telephones.
Ball lightnings can exist in an all-metal enclosure such as the interior
of an airplane (Uman, 1968).
- Demise
- Ball lightnings decay in one of two modes, either silently or
explosively. The explosive decay takes place rapidly and is accompanied
by a loud noise. The silent decay can take place either rapidly or
slowly. After the ball has decayed, it is sometimes reported that a
mist or residue remains. Occasionally a ball lightning has been
observed to break up into two or more smaller ball lightnings.
- Types
- There may be more than one type of ball lightning. For example, the
ball lightning that attaches to conductors may be different from the
free-floating ball lightning; and the ball lightning that appears near
ground may be different from the ball lightning that hangs high in the
air or the ball lightning that falls out of a cloud.