Ern Mainka - Photography - Ball Lightning

	Abstract from JOURNAL OF METEOROLOGY Vol. 21, no. 214, December 1996 REPRODUCIBILITY IN THE FORMATION OF LIGHTNING BALLS By D.J.TURNER, LA.C., University of Bristol, U.K. present address: Condensation Physics, PO Box 232, Huntingtown, Maryland, 20639, USA. Until recently, the characteristic behaviour of ball lightning presented a serious problem to scientists. It seemed that, in order to explain all the reliable observations, a single phenomenon could not be accommodated within the known laws of physics (Singer, 1971; Barry, 1980; Smirnov, 1987). Stakhanov (1979) had proposed certain assumptions from which most of the properties could be explained if only low internal temperatures and energy densities were accepted. A new model for the structure and stability of the phenomenon has now been presented which appears to remove these limitations (Turner, 1994). It does this by a fuller treament of the thermodynamics. However, it does not specifically address the problem of why the balls are so difficult to produce. A hitherto unreported observation is presented which may have a bearing on this matter in indicating some of the main variables which need to be controlled. Although it is not usually referred to as a property of ball lightning, a very significant characteristic is the extreme difficulty in preparing the phenomenon in the laboratory. Clearly, this characteristic contributes to the excessive scepticism which surrounds even the existence of ball lightning. Despite many attempts over the last two centuries, no-one has yet succeeded in intentionally producing fully characteristic ball lightning. Since the stabilizing mechanism of an established ball now seems so robust (Turner, 1994), it can only reasonably be assumed that the problem lies in the initiation stages. Furthermore, the model suggests one reason for the difficulty in preparing ball lightning in the laboratory. This has been the failure to recognize that its stability has equally important electrical, hydrodynamic and chemical aspects. Nature appears to find it somewhat easier to balance these influences than scientists do. However, even the natural phenomenon is not usually made reproducibly. For this reason, the writer became very interested when he heard of a most unusual display which had apparently taken place in the Great Australian Bight in late July 1956. The occurrence was described by a witness who had read a brief preliminary account of the author's model (Chown, 1993). From subsequent correspondence, which has been fairly extensive, I am convinced that the description is as accurate as could possibly be expected after this length of time. The display was observed by the crew of a fishing vessel and was conveyed by one of the men, Mr. Keith H. Hill, who is now a fishery consultant. It is perhaps relevant to mention that much less spectacular, though basically very similar, accounts covering most aspects of the description have been given by mariners and others over the last two centuries (Arago, 1855; Blanc, 1877; Hayden, 1888; Singer, 1971). It is also relevant that professional seamen are normally well used to the careful observation of weather conditions and to the assessment of sizes and distances. In order to avoid the risk of interposing any personal interpretation on the accouut or leaving out anything which may later prove useful, I will quote directly from Mr. Hill's first letter: "....We were between Coffin Bay Peninsula and Flinders Island, travelling N.W. with a hard Northerly of half gale strength coming off the land some 25 miles away, with a rotten steep 4-5 metre wave giving us a belting. The cloud height was seemingly 1000 feet above us, a solid dark grey rippled even mass from horizon to horizon, as the sun was setting. " Right after sunset, the electrical storm began, with large balls of lightning coming from the cloud base, dropping to the sea in 2 to 3 seconds of activity. These rather large balls seemed to be about one metre diameter occurring every 3 to 10 seconds, to within 100 metres (but fortunately not on our vessel!) to some miles away. The display allowed us to dispense with our compass sighting as so many times the sky was alight. We could see even thirty miles ahead to Flinders island and reefs surrounding with ease. The balls of lightning were of a sodium yellow colour internally with a bright active lilac blue surface of electrical energy. .... The display continued for over two hours, so we saw at least 1,000 individual displays. Our eyes were effected to some degree, as the black night that followed seemed the blackest we had known and special care was taken in navigation until dawn arrived, with two on watch." Nature had obviously got everything right in this case, but the storm was clearly not an ordinary thunderstorm. In addition to the unusual cloud structure, subsequent correspondence revealed that neither rain nor ordinary lightning accompanied the display. Mr. Hill originally suggested a number of possible sources of dust which might be relevant. However, from his subsequent informal investigations of meteorological records, it does not seem possible to be at all precise about a source. All that can be concluded is that the wind probably did carry dust particles to the area from one of the southern or central Australian deserts. The dust must have come from a considerable distance, most of it presumably over arid land. Thus it would have been given ample opportunity to become separated into well dispersed clouds of particles having similar size, shape and perhaps composition. The dust clouds would then pick up water in the humid regions near the coast and eventually become the evenly spread clouds described above. Presumably, the exceptionally reproducible production of lightning balls in this case is due mainly to the presence of electric fields exactly matched to the dimensions of the dust particles in the cloud and to the dust concentration. These could presumably initiate electrical breakdown of the air at a rate which was unusually reproducible over the whole area of the dust containing clouds. This rate must have been optimal for forming the specific metastable species required for thermochemical refrigeration. REFERENCES ARAGO, F, 1855 Meteorological essays. (transl. R.A. Sabine), Brown, Green and Longmans, London. BARRY, J.D., 1980, Ball lightning and bead lightning. Plenum Press, New York. BLANC, E., 1877 Ball lightning, Nature 15,539. A summary from Comptes Rendus. 84, 666-667. CHOWN, M., 1993 Fire and water: a recipe for ball lightning. New Scientist, 137,(20 Mch), pl8. HAYDEN, E., 1888 Globular lightning. Science 11, p 110. SINGER, S., 1971, The nature of ball lightning. Plenum Press, New York. SMIRNOV, B.M., 1987 The properties and the nature of ball lightning. Phys. Repts. 152,177-226. STAKHANOV, LP, 1979 The physical nature of ball lightning. Atomizdat, Moscow. CEGB Translation (227 pages), CE 8244 TURNER, D.J., 1994 The structure and stability of ball lightning. Phil. Trans. Roy. Soc. A. 347, 83-111.