Ball lightning may be more exotic than microwave oven sparks, but most scientists are convinced that it is no less real. Martin A. Uman, chairof the department of electrical computer engineering at the University of Florida at Gainesville explains:
"Ball lightning is awell-documented phenomenon in the sense that it has been seen and consistently described by people in all walks of life since the time of the ancientGreeks. There is no accepted theory for what causes it. It does not necessarily consist of plasma; for example, ball lightning could be the result of achemiluminescent process. The literature abounds with speculations on the physics of the ball lightning."
Peter H. Handel in thedepartment of physics and astronomy at the University of Missouri at St. Louis provided a detailed overview and advances his favored model ofball lightning:
"According to statistical investigations carried out by J. R. McNally in 1960 (J. R. McNally, "Preliminary Report on BallLightning" in Proceedings of the Second Annual Meeting of the Division of Plasma Physics of the American Physical Society, Gatlinburg,No. 2AD5 [1960], Paper J-15, pp. 1AD25), ball lightning has been seen by 5 percent of the population of the earth. This percentage is about the sameas the fraction of the population that has seen an ordinary lightning strike at close range--that is, close enough to see the direct point of thelightning impact.
"Ball lightning was seen and described since antiquity, often by groups of people, and recorded in many places. It is in generaldescribed as a luminous sphere, most often the size of a small child's head. It appears usually during thunderstorms, sometimes within a fewseconds of lightning but sometimes without apparent connection to a lightning bolt. In some cases, ball lightning appears after a thunderstorm--oreven before it. Its lifetime varies widely, ranging from a few seconds to several minutes; the average duration is about 25 seconds. The lifetime ofball lightning tends to increase with size and decrease with brightness. Balls that appear distinctly orange and blue seem to last longer thanaverage. Many of these general characteristics are based on the work of A. I. Grigoriev, who analyzed more than 10,000 cases of ball lightning (A.I.Grigoriev, " Statistical Analysis of the Ball Lightning Properties," in Science of Ball Lightning, edited by Y. H. Ohtsuki, World ScientificPublishing Co., Singapore, 1988, pp. 88AD134).
"Ball lightning usually moves parallel to the earth, but it takes vertical jumps. Sometimes itdescends from the clouds, other times it suddenly materializes either indoors or outdoors or enters a room through a closed or open window,through thin nonmetallic walls or through the chimney. When it passes through closed windows, the lightning ball damages them with small holesabout one third of the time. The balls have no observable buoyancy effect. All these attributes led the great Russian physicist Pyotr Kapitsa in 1955to interpret ball lightning as an electrodeless discharge caused by a standing UHF waves of unknown origin present between the earth and thecloud; earlier versions of this idea date back to the 1930s.
"Scientists have since refined Kapitsa's speculation. The Maser-Soliton Theory,which I first described in 1975 (P.H. Handel, "Maser Theory of Ball Lightning" in Bulletin of the American Physical Society Series II, Vol. 20[1975], No. 26), is the present-day version of the UHF discharge approach. I have been directing research on the Maser-Soliton Theory at theKurchatov Scientific Center in Moscow since 1992. According to this theory, outdoor ball lightning is caused by an atmospheric maser-- analogousto a laser, but operating at a much lower energy--having a volume of the order of many cubic kilometers.
"In technical terms, the maser isgenerated by a population inversion induced in the rotational energy levels of the water molecules by the short field pulse associated with streaklightning. The large volume of air that is affected by the strike makes it difficult for photons to escape before they cause 'microwave amplificationby stimulated emission of radiation' (the maser effect). Unless the volume of air is very large or else is enclosed in a conducting cavity (as is the caseof ball lightning in airplanes or submarines and to a certain degree also indoors), collisions between the molecules will consume all the energy ofthe population inversion. If the volume is large, the maser can generate a localized electrical field or soliton that gives rise to the observed balllightning. Such a discharge has not yet been created in the laboratory, however.
"The Maser-Soliton Theory is supported by three well-knownfacts. First, ball lightning never occurs on sharp mountain peaks, high-rise buildings and other high points that attract lightning and that are usedfor lightning research by specialists in atmospheric electricity. (Lightning researcher Karl Berger told me he spent his life registering and measuringhundreds of thousands of lightning discharges hitting his laboratory on top of Mount Salvatore in Lugano, Italy, without getting a trace of balllightning.) The inability to observe ball lightning in such settings has led to widespread frustration and even skepticism about the reality of thephenomenon. But in fact, the field pulse of the lightning striking high, peaked objects is localized in a narrow cone that encloses a relatively smallvolume. According to the Maser-Soliton Theory, this environment precludes the maser effect. On the other hand, when lightning strikes theflatlands, the resulting field pulse is huge: about 10 kilometers wide and three kilometers high. Ball lightning thus keeps its secrets: it visits thefarmer and avoids the scientist!
"Second, ball lightning is harmless inside airplanes and submarines or in homes that have a conducting frame.Again according to the Maser-Soliton Theory, the energy of the maser in such settings is limited to about 10 joules (contrasted to a limit of109 to 1010 joules in the open air), too little to be dangerous to life.
"And third, open-air ball lightning oftenends with a violent explosion, sometimes causing extensive damage. The explosion is particularly strange because it violently displaces conductingobjects to a larger degree than dielectrics. For instance, electric connection boxes are sometimes extracted from within the walls of houses byoutdoor ball lightning and thrown in the middle of the street. The Maser-Soliton Theory predicts that such spiking would occur when the loadsuddenly disappears. (When the discharge that was consuming the photons generated by the maser suddenly disappears, these photons get to livelonger and to multiply instantly, unbounded by the maser effect. This proliferation triggers an even larger instantaneous avalanche of photons anda practically instantaneous exponential growth of the electrical field. The increase occurs too rapidly to cause electric breakdown or heating butcould cause very large ' ponderomotive forces'--mechanical effects that can tear apart composite objects having varied dielectric constants.)
"The pioneering UHF discharge ball-lightning experiments of Ohtsuki and Ofuruton in Japan (Y. H. Ohtsuki and H. Ofuruton, 'PlasmaFireballs Formed by Microwave Interference In Air' in Nature Vol. 350 (1991), page 139) and the above-mentioned research at Kurchatovin Moscow (V. A. Zhil' tsov, C9. A. Manykin, E. A. Petrenko; and A. A. Skovoroda, J. F. Leitner and P. H. Handel, 'Spatially Localized MicrowaveDischarge in the Atmosphere,' in JETP Vol. 81 [1995] ,pp. 1072-81) have aided in the solution of the ball-lightning enigma. Now that weseem to understand the true nature of ball lightning, it is particularly unfortunate that no funds are available in the U.S. for the study and thecontrolled reproduction of this fascinating phenomenon.
"A focal point for ball-lightning research will be the Fifth International Symposiumon Ball Lightning on August 26-29, 1997, organized by Y. H. Ohtsuki and H. Ofuruton from Tokyo Metropolitan College of AeronauticalEngineering (for information, send e-mail to ofuruton@kouku-k.ac.jp). I will be the U.S.ball-lightning representative on the International Committee; I can be contacted at handel@jinx.umsl.edu"
The scientific community is increasinglyconvinced that ball lightning is a real phenomenon (although there remain some skeptics). What could cause ball lightning, on the other hand, is asource of steady controversy. Earlier, we ran the above theory. John Lowke, a plasma physicist at the Institute of Industrial Technologies, CSIRO,in Australia, offers another theory about the phenomenon:
"Although there is at least one textbook on lightning that questions theexistence of ball lightning and I have never seen the phenomenon personally, I feel that there is no question that ball lightning exists. I have talkedto six eyewitnesses of the phenomena and think there is no reasonable doubt as to the authenticity of their observations. Furthermore, the reportsare all remarkably similar and have common features with the hundreds of observations that appear in the literature.
"Ball lightning istypically described as a luminous ball one to 25 centimeters in diameter having about the intensity of a 20-watt incandescent lamp; the phenomenonusually occurs after a lightning strike. It almost always moves, has a top speed of about three meters per second and floats about one meter abovethe ground. The motion can be counter to the prevailing breeze and can change direction erratically. Ball lightning may last up to 10 seconds,whereupon the ball extinguishes either noiselessly or with a bang. There have been many observations of ball lightning inside of houses and even inairplanes. There have also been a number of observations of ball lightning passing through closed glass windows, with no apparent damage to theglass. Usually there is no discernible heat production, although a recent observation reported a wooden plank that was singed. Several peoplehave reported the smell of ozone and nitrogen oxides associated with ball lightning and also static in a transistor radio.
"Scientists havestruggled for decades to formulate a plausible explanation for the existence of a stable plasma ball. A hot globe of plasma should rise like a hot-airballoon, yet observations do not generally report such behavior. Why does such a ball move, usually counter to the wind? What energy sourcesustains the lightning ball, given that such a ball would be expected to diminish rapidly in intensity?
"There have been hundreds of papers, andat least three books, discussing ball lightning. Most theories raise more questions than they claim to solve. Probably the most famous theory wasadvanced by the Russian Nobel Prize winner Pyotr Kapitsa, who claimed that ball lightning is caused by a standing wave of electromagneticradiation. But why should there be a standing wave of electromagnetic radiation? Other theories assert a variety of sources of energy for balllightning, including atomic energy, antimatter, burning material or the electrical field from a cloud.
"There is no generally accepted theory ofball lightning. I have my own theory, published in the Journal of Physics D: Applied Physics, ("A Theory of Ball Lightning as an ElectricDischarge" in Vol. 29, No. 5, pages 1237-1244; May1996). I propose that ball lightning is powered by the electrical field associated with dispersingcharges in the earth after a lightning strike. The movement of the ball is controlled by the velocity of the electrical charge as it disperses in theground after the initial period of electrical 'breakdown' that occurs at the moment of the strike. In my paper, I suggest that this discharge is similarto a corona discharge (as occurs around high-voltage transformers) and consists of a succession of electrical pulses that take place on amicrosecond time scale.
