- Not many people get to see ball lightning,
but those who do never forget it. Imagine a glowing orb suddenly materializing
in front of you, possibly sizzling or exuding a bluish mist and an acrid
smell. The globe may be larger than a beach ball and dart through the air,
perhaps hovering occasionally as if considering its next move. The ball
may also roll or bounce along the ground, climb utility poles, and skitter
along power lines. As it travels, the fiery sphere may destroy electrical
equipment, ignite fires, and even singe animals or people.
-
- THE SHINING. An extraordinarily large-about
100 meters in diameter-object presumed to be ball lightning was caught
on film by a park ranger in Australia. It lasted surprisingly long, about
5 minutes. Abrahamson
-
- After only 10 seconds or so, the apparition
typically vanishes abruptly. Some balls flick out in silence, like a lamp
turning off. Others burst with sharp bangs and fiery streamers.
-
- Despite half-a-millennium's worth of
anecdotal reports and two centuries of scientific investigations, no one
yet can say for sure just what ball lightning is. Lately, however, a small
group of researchers has developed theories and reported experimental results
that appear to explain some features of ball lightning that previous models
couldn't account for.
-
- Most eyewitness reports point to ordinary
lightning as the trigger, but other electric discharges have also been
implicated. What happens next depends on the theorist.
-
- These researchers agree that an aerosol,
a suspension of fine particles in air, is present in the balls. The particles
react chemically and interact electromagnetically. Some of the theorists,
however, picture a radiant network of filaments-a "fluff ball of fire,"
as one scientist described it. Another contends that the aerosol is an
acid mist and that it encloses a gaseous, hot core of reactive chemicals.
In all the models, the aerosol's action is critical in explaining the litany
of often astonishing eyewitness accounts.
-
- Alternative to plasmas
-
- Documented sightings of ball lightning
date back to the Middle Ages. A Russian databank includes about 10,000
reports from the past several decades. In recent years, as science failed
to decipher the phenomenon, pseudoscientific explanations have abounded.
Those include matter-antimatter annihilations, clumps of the exotic dark
matter of the universe, and spontaneous bursts of nuclear fusion.
-
- Ball lightning has "a big kook following
and a scientific following because it's one of the great unexplained mysteries,"
says Martin A. Uman of the University of Florida in Gainesville, who has
studied lightning for some 30 years.
-
- Of the many scientific theories of ball
lightning, most depict the phenomenon as some kind of plasma, or hot gas
of electrons and positively charged atomic or molecular ions. That's a
reasonable expectation since ball lightning generally has been reported
to occur along with thunderstorms whose ordinary lightning bolts ionize
the air, creating columns of plasma along their paths.
-
- Nonetheless, pure-plasma models for ball
lightning are plagued by difficulties. "None of them works,"
scowls Graham K. Hubler, a physicist and materials scientist at the Naval
Research Laboratory (NRL) in Washington, D.C. He saw ball lightning 42
years ago as a 16-year-old, and he has never forgotten the experience.
"You're just so startled you can't move," he recalls of the moment
a whitish-yellow ball about the size of a tennis ball suddenly appeared
in front of him one night in a park in upstate New York.
-
- One major challenge to the plasma explanation
for ball lightning is that plasma always expands unless great pains are
taken to confine it. Fusion researchers "build enormous [reactors
called] tokamaks to do that sort of thing-to contain a plasma for a second"
within a magnetic field for nuclear fusion experiments, Hubler notes (SN:
3/18/00, p. 191).
-
- "Hot plasma in air has two tendencies-to
disappear and to go up," says physical chemist David J. Turner of
Condensation Physics in Huntingtown, Md., a retired electric utility researcher
who became interested in ball lightning while studying the behavior of
ions in steam. The oppositely charged particles that make up the plasma
tend to rapidly recombine, quickly annihilating it. Moreover, the buoyancy
of hot plasma in air, which would make a ball rise, doesn't jibe with ball
lightning's hovering, rolling, and flying horizontally, Turner adds.
-
- He suggests that one way out of the conundrum
is to add features of an aerosol to a plasma theory of ball lightning.
An aerosol's additional material can form a structure, host long-lasting
chemical reactions, store electric charges, and otherwise account for observed
ball-lightning properties, Turner and others argue.
-
- Says Turner, "I don't think you
can explain all the properties [of ball lightning] without accepting that
it's an aerosol-related phenomenon."
-
- Dirty secret
-
- The notion that aerosols may be a part
of ball lightning goes back to at least the 1970s, but it's currently winning
unprecedented attention.
-
- BALL OF NANOTWINE? An electron microscope
image of residue on a filter from vaporized soil shows filaments of nanoscale
particles, such as those proposed in a ball lightning theory. Abrahamson
-
- Some of the theories don't include a
plasma after the original lightning strike. Two years ago, chemical engineers
proposed a specific and plausible mechanism by which a lightning strike
on soil could produce an aerosol type of ball lightning. John Abrahamson
of the University of Canterbury in Christchurch, New Zealand, and James
Dinniss, who's now at the household chemicals firm Lever Rexona in Petone,
New Zealand, described their hypothesis in Nature and reported on experiments
that seemed to support it.
-
- Hubler said in a commentary accompanying
the report, that the model is the first that "can explain most aspects
of ball lightning."
-
- Besides giving a boost to aerosol interpretations
of ball lightning, the findings prompted people around the world-many of
them scientists or engineers-to contact Abrahamson with previously undocumented
eyewitness accounts of the phenomenon. The findings also sparked further
research, as well as new collaborations among the handful of aerosol ball-lightning
investigators.
-
- A variety of articles on ball lightning,
including descriptions of the current aerosol theories and a collection
of the new eyewitness reports, appears in the January Philosophical Transactions
of the Royal Society London A. Abrahamson, who was guest editor of the
one-theme issue, says it "probably doubles the number of [published]
observations . . . by scientifically trained people."
-
- "You could say that Abrahamson and
[his] theory have revived interest in ball lightning in general,"
says Uman. The model invented by Abrahamson, a specialist in reducing the
dust content of factory air, and Dinniss, his former student, has been
dubbed by Hubler as the fluff-ball model. They revisited an old hypothesis
that ball lightning might contain a fine network of metal particles. They
built upon that idea by formulating a specific sequence of chemical reactions
that could be triggered by a lightning strike on soil and generate such
networks.
-
- Specifically, they proposed that when
a lightning bolt vaporizes silicon dioxide-a common mineral in soil-reactions
with carbon compounds transforms it into nanometer-scale pure-silicon droplets.
Such reactions also underlie the smelting of many rocky ores into metal.
-
- Once formed, the silicon particles would
react with oxygen and become coated with an insulating skin. In the highly
charged atmosphere of an electrical storm, the oxide-coated nanoparticles
would then pick up polarized electrical charges and form loose-knit networks
of filaments-the "fluff balls" of Hubler's commentary.
-
- By calculating the heat and light that
those wispy, charge-laden balls would generate, the team determined that
a plausible ball roughly the size of a basketball would last 3 to 30 seconds
and glow like a 100-watt bulb-conditions often reported by those who have
observed ball lightning. Without a protective layer, oxidation of bare
metal nanoparticles would be expected to proceed more quickly and at higher
temperatures than observations of typical ball lightning have described.
That oxide layer ought to keep fresh oxygen from diffusing too quickly
to the underlying silicon. That slows the reactions and reduces the energy
output.
-
- Uman says the theory is promising, but
he suspects that it has gaps. He and fellow lightning researchers have
been within 100 meters of ground strikes hundreds of times, he notes. They
should have seen ball lightning at least a few times if the New Zealanders'
theory is correct, Uman argues. What's more, both he and Hubler say, the
New Zealand team's model for how the charged filaments assemble into ball-shaped
structures is less than compelling.
-
- Abrahamson counters that additional support
for the model has recently come from other fields, particularly from microgravity
experiments on granular materials. In fact, in the May Journal of Electrostatics,
he and geologist John Marshall of the SETI Institute in Mountain View,
Calif., will present a novel explanation-with supporting experimental evidence-of
how electrical forces can build filament networks.
-
- Different strokes
-
- Six years before Abrahamson and Dinniss
published their model, Vladimir L. Bychkov of the Russian Academy of Sciences'
Institute for High Temperatures in Moscow proposed that ball lightning
consists of a loose, porous aggregate of particles. In his theory, the
heat and light come mainly from electric effects, not oxidation.
-
- Bychkov presents the latest version of
his theory alongside an updated version of the New Zealand model in the
Transactions issue on ball lightning. In Bychkov's theory, lightning can
transform many organic materials in the environment-not just metal residues
from the soil-into airborne polymer threads. Once that happens, he surmises,
the threads could tangle up into a spongy ball. As long as the materials
in the tangles are electrical insulators, or dielectrics, such a ball can
hold electric charges in place and permit huge buildups of energy on the
ball's surface, Bychkov argues. The energy is stored in well-separated
patches-a mosaic-of positive charges and negative charges, he says.
-
- Once a ball forms, it could yield heat
and light when high voltages begin breaking down gases near the surface.
That process could create the orange or blue coronas that some observers
have witnessed. The enormous charge buildup also could intermittently force
electric currents through some of the threads in the ball itself, making
them glow like light-bulb filaments.
-
- Turner's theory, also updated in Transactions,
holds that ball lightning contains a hot plasma as its main energy source
and that the sphere maintains its shape without any network of interconnected
filaments. Instead, electrically charged ions from the plasma drift outward
and cool, collecting water molecules along the way. This hydration of the
ions transforms them into acidic moisture droplets-aerosol particles. Ultimately
an electrically charged shell of those droplets encloses the plasma, all
the while absorbing ions from it and causing the internal pressure of the
plasma within the shell to fall. The resulting inward pressure from the
air maintains the ball's shape.
-
- Both Bychkov and Turner claim that their
theories can account for the small but significant number of reports of
so-called high-energy ball lightning. In those reports, the fiery orbs
land in liquids and boil them away or sear through glass, metal, trees,
or even people.
-
- As first proposed 2 years ago, the New
Zealand team's model could not accommodate the higher-energy balls. But
now, Abrahamson argues that his model can explain high-energy balls under
certain unusual conditions, such as when there's a lightning strike or
a powerful electric discharge on a fuse box or other closely confined metal
object. The resultant balls would be richer in metal fuel than those produced
by a strike on soil and therefore would burn hotter.
-
- Abrahamson notes a precedent for this.
U.S. military scientists have devised as potential missile decoys for warplanes
balls of aerogel (SN: 12/14/96, p. 383) -an extremely porous and lightweight
substance-whose surfaces inside and out are coated with a thin film of
iron. Normally packed in inert gas, the balls spontaneously oxidize when
they hit the air, emitting missile-fooling infrared radiation. NRL's Celia
I. Merzbacher, one of the inventors of the balls, describes them in the
Transactions issue. (For related video clips, see http://www.sciencenews.org/20020209/balllightning.asp)
-
- Seeing is believing
-
- "If we want to understand ball lightning,
we need to be able to make and control it in the laboratory," says
Turner in his Transactions report.
-
- "This is the acid test of any theory,"
Abrahamson agrees.
-
- As a starting point for tests of aerosol
theories, scientists note that lightning strikes have long been known to
create glassy walled, hollow tubes just under the ground's surface. The
tubes, known as fulgurites (SN: 3/20/93, p. 184), form where lightning
discharges melt and vaporize soil along their paths. For at least 30 years,
researchers have suspected that materials from such cavities might play
a role in ball lightning.
-
- HOT STUFF. In a Russian experiment, a
floating, baseball-size fireball coalesces from vapors of wax and resin
that were disintegrated by an electric discharge. The ball survived for
almost half a second. Bychkov
-
- In Soviet experiments reported in 1977,
laboratory researchers used up to 12,000 volts to vaporize the inner walls
of tubes of ice or plastic that served as models of fulgurites. Once enough
pressure built up in the tube to rupture a thin plastic diaphragm, brilliant
balls up to 400 mm in diameter came flying out. Although they were in the
size range of natural ball lightning, the specimens were much too bright
and lasted only a few milliseconds, the scientists reported.
-
- Subsequent experiments by Bychkov and
his colleagues also have produced fiery balls. For example, electric discharges
vaporized material from the walls of wax or plastic tubes. When that plasma
hit a metal, tiny balls glowing yellow or yellowish-red appeared, but none
of them lasted longer than a fraction of a second.
-
- Instead of plastic and other surrogates
for soil, Abrahamson and Dinniss tested their hypothesis with actual dirt.
They packed it onto shallow, electrically conductive platters and zapped
it with up to 20,000 volts. As they had predicted, chains of nanometer-scale
particles formed. To find them, the scientists pumped the air above the
soil beds through filters just as the electrical discharge took place.
Using an electron microscope, the researchers detected thread-like chains
caught in the filters.
-
- In more-recent experiments described
in the Transactions issue, Abrahamson and his colleagues carried out discharges
on deeper, narrower soil beds. The beds were insulated on top so that a
fulgurite-like cavity could form when the soil vaporized. Although none
of 24 tests produced luminous balls, two of the discharges generated short-lived,
donut-shape puffs of material, like glowing smoke rings. Those shining
loops may be precursors to ball lightning formation, Abrahamson conjectures.
-
- Neither he nor Turner has had the privilege
of seeing ball lightning. "I do badly want to see it," Turner
confesses.
-
- Adds Abrahamson, "I won't be satisfied
until we've got all the conditions right to achieve a [soccer-ball]-sized
ball lightning in the lab." With luck, they or some other fortunate
scientist may soon transform ball lightning from a rare apparition into
an everyday acquaintance. ___
-
-
- References
-
- Fiery blasts: QuickTime video clips.
-
- Abrahamson, J. 2002. Ball lightning from
atmospheric discharges via metal
- nanosphere oxidation: From soils, wood
or metals. Philosophical
- Transactions of the Royal Society A 360(Jan.
15):61-88.
-
- ______. 2002. Chemical models of ball
lightning from atmospheric
- electricity. Available at
- http://www.pubs.royalsoc.ac.uk/phil_maths/news/balllight.html.
-
- ______. 2002. Preface. Philosophical
Transactions of the Royal Society A
- 360(Jan. 15):3.
-
- Abrahamson, J., A.V. Bychkov, and V.K.
Bychkov. 2002. Recently reported
- sightings of ball lightning: Observations
collected by correspondence and
- Russian and Ukranian sightings. Philosophical
Transactions of the Royal
- Society A 360(Jan. 15):11-35.
-
- Abrahamson, J., and J. Marshall. In press.
Permanent electric dipoles on
- gas-suspended particles and the production
of filamentary aggregates.
- Journal of Electrostatics.
-
- Abrahamson, J., and J. Dinniss. 2000.
Ball lightning caused by oxidation of
- nanoparticle networks from normal lightning
strikes on soil. Nature
- 403(Feb. 3):519.
-
- Bychkov, V.L. 2002. Polymer-composite
ball lightning. Philosophical
- Transactions of the Royal Society A 360(Jan.
15):37.
-
- Bychkov, A.V., V.L. Bychkov, and J. Abrahamson.
2002. On the energy
- characteristics of ball lightning. Philosophical
Transactions of the Royal
- Society A 360(Jan. 15):97-106.
-
- Hubler, G.K. 2000. Fluff balls of fire.
Nature 403(Feb. 3):487-488.
-
- Merzbacher, C.I. 2002. Materials that
emit light by chemical reaction.
- Philosophical Transactions of the Royal
Society A 360(Jan. 15):89-96.
-
- Singer, S. 2002. Ball lightning-the scientific
effort. Philosophical
- Transactions of the Royal Society A 360(Jan.
15):5-9.
-
- Turner, D.J. 2002. The fragmented science
of ball lightning (with comment).
- Philosophical Transactions of the Royal
Society A 360(Jan. 15):107-152.
-
- Further Readings:
-
- Weiss, P. 2000. Neon gives healthy glow
to reactor. Science News 157(March
- 18):191.
-
- Wu, C. 1996. Aerogel films as electronic
insulators. Science News 150(Dec.
- 14):383.
-
- ______. 1993. In the wild, a bolt of
'bucky' luck. Science News 143(March
- 20):84.
-
- Sources:
-
- John Abrahamson
- Chemical and Process Engineering Department
- University of Canterbury
- Private Bag 4800
- Christchurch
- New Zealand
-
- Vladimir L. Bychkov
- Institute for High Temperature
- Russian Academy of Sciences
- Izhorskaya 13/19
- Moscow 127412
- Russia
-
- James Dinniss
- Process Engineer
- Lever Rexona
- Private Bag 1
- Petone
- New Zealand
-
- Graham K. Hubler
- Naval Research Laboratory
- Code 6370
- 4555 Overlook Avenue, S.W.
- Washington, DC 20375
-
- John Marshall
- SETI Institute
- NASA Ames Research Center
- Moffett Field, CA 94035-1000
-
- Celia I. Metzbacher
- Naval Research Laboratory
- Code 1004
- 4555 Overlook Avenue, S.W.
- Washington, DC 20375
-
- Stanley Singer
- Athenex Research
- 381 South Meridith Avenue
- Pasadena, CA 91106-3576
-
- David J. Turner
- Condensation Physics
- 3435 Plum Point Road
- Huntington, MD 20639
-
- Martin A. Uman
- Department of Electrical and Computer
Engineering
- University of Florida
- 216 Larsen Hall
- P.O. Box 116200
- Gainesville, FL 32611-6200
-
-
- From Science News, Vol. 161, No. 6, Feb.
9, 2002, p. 87.
-
-
- Copyright ©2002 Science Service.
All rights reserved.
- 1719 N St., NW, Washington, DC 20036
- 202-785-2255
- scinews@sciserv.org
-
- http://www.sciencenews.org/20020209/bob8.asp
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