Ball lightning.

Abstract

Ball lightning is alleged by some to be a rare atmospheric phenomenon usually associated with thunderstorms, while others hold that it does not exist. This controversy has continued for centuries. This study comprises a critical evaluation of evidence for the existence of ball lightning. An historical review of the controversy is first presented, giving a chronological account of developments in ball lightning theories and of important observations alleged to be of the phenomenon. Other phenomena which might be mistaken for ball lightning are then subjected to a more detailed study than has hitherto been published, and the means by which such misidentifications could be recognized areestablished. A discussion of psychological and perceptual aspects indicates that descriptions could not always be taken at face value, and that many accounts of alleged ball lightning would be expected to contain substantial inaccuracies. The original intention to evaluate cases of alleged ball lightning already published in scientific journals was abandoned because there was no standardisation of information content, and because the majority of reports contained insufficient information for evaluation. Many reports had been written in a style which indicated an assumption that ball lightning was the cause of the event. Approximately 200 unpublished reports were therefore collected and subjected to evaluation. It was found that the majority of reports of alleged ball lightning could be explained by other means, and there was only a very small residue of reports which could not easily be thus explained. A large proportion of the reports could be attributed to corona discharge effects such as St Elmo's fire, or by familiar effects of conventional linear lightning. The validity of many previously published statistical studies of ball lightning was shown to be doubtful. The thesis concludes with a comparitive discussion of the merits and demerits of some of the diverse physical models which have been proposed to explain the properties of ball lightning.