The existence of ball lightning has been hard to confirm by scientists due to the lack of verifiable observations and photographs of the phenomenon. Few will completely deny that ball lightning exists, but those that believe that ball lightning does occur in natural circumstances have not yet been able to formulate conclusive theories.
Although it's not yet known exactly what ball lightning is, it is known, however, what is not ball lightning. With the growth of the information age came more numerous reports of ball lightning sightings, but most are found to be cases of mistaken identity with one of the following two occurances:
- Power Line Faults - When a short-circuit (fault) occurs on an energized power system, a bright arc results. The arc is extremely intense, and can seem to illuminate an entire sky at night and be clearly visible during the day. Faults are very common events, and can be caused by high winds, ice, a direct lightning strike, birds or squirrels, or an automobile striking a utility pole - all of which will produce the bright blue-green arc. Faults can occur anywhere along power lines, not just at transformers or substations.
Video clip of lightning-triggered flashover
Windows Media, 157KB
Faults are often mistaken for lightning, and since they appear as a bright ball of light near the ground, are often reported as ball lightning. Video footage of tornadoes and high winds often contains instances of power line faults that are incorrectly categorized as a type of lightning flash due to their bright nature (sometimes illuminating the entire funnel of a tornado). A short-circuit involving tens of thousands of amps is indeed very bright and extremely hot, and sometimes will generate fireballs and sparks by igniting or overheating nearby materials.
A type of fault known as a lightning-caused 'flashover' can be particularly miscategorized as ball lightning since it occurs in conjunction with a lightning strike to a power system. Flashovers can occur anywhere along a power line, they don't always occur at transformers - and can occur at great distances from the point that the lightning actually hit the line (see the PTI link below).
[ more info on flashovers ]
The following are the most common observations that result in power line faults being miscategorized as ball lightning:
OBSERVATION: "The ball of light moved several feet"
There are four reasons that can cause an arc to move:
- Wind pushing the arc or any resultant fireball sideways.
- The arc will heat the surrounding air, causing the air to rise and carry the arc with it (Think of the 'Jacob's Ladder' device seen in mad scientist movies, where the little spark slowly moves upward between two probes due to thermal bouyancy).
- The wires and poles are moving or collapsing due to wind or falling trees, causing the short circuit contact point to move or occur in different locations.
- 'Motoring' forces caused by magnetic fields associated with the arc.
OBSERVATION: "The ball of light was on a power line, but not at a transformer."
THE CAUSE: Faults (short circuits) can occur at any location along a power line, not just at transformers. Lightning-triggered flashovers can occur across any insulator on a line, including those at poles without transformers (see photos at the PTI web site). Faults can also occur anywhere where wind, trees, or animals have caused a short circuit.
OBSERVATION: "The ball of light seemed too bright and intense to be power-line related."
THE CAUSE: The current in some power line faults can approach 100,000 amperes - which is not much less than current in a lightning bolt! This makes for an extremely intense arc that can significantly light up the sky at night and even during the day, and can be visible for miles. Faults caused by the winds in a tornado's vortex can illuminate the entire funnel from the inside and out.
Power Technologies, Inc. carried out an extensive study on the effects of lightning-triggered flashovers, capturing many such events on special cameras set up along power lines. View their web site here.
- Lightning Photography - Some lightning photographs have been incorrectly used as evidence for ball lightning due to an anomaly that occurs on some images.
A cloud-to-ground lightning strike doesn't terminate at a point on the cloud base, it extends deep inside the cloud into a network of branches. When a lightning bolt passes through a cloud into clear air, the point of exit on the cloud is often illuminated brightly by the lightning channel. On lightning photographs, this 'exit point' often overexposes on the film, appearing as a bright ball of light connected to the lightning channel - which is another common source for mistaken ball lightning reports (see photos below).
Portions of a lightning discharge behind a cloud can also illuminate a cloud in the same way. Power line flashovers (as described above) caused by a lightning strike may overexpose in a photo in the area of the base of the lightning channel, appearing as a ball of light at the ground.
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