The mechanism of a thunderstorm

Abstract

In 1909 I described a theory of the origin of the electricity in thunderstorms based on the observation that when a drop of water is broken up in the air the water obtains a positive charge while the corresponding negative charge is given to the air. Little attempt was then made to work out the details of the processes involved in a thunderstorm; only the most general consideration was given to the quantities involved and no description of the nature of the lightning discharges was attempted. This was mainly because very little was then known of the air currents in a thunderstorm and still less of the associated electrical fields. Recently a number of papers have been published recording the electrical fields associated with thunderstorms and the sudden changes in the field which accompany lightning discharges. The authors of these papers have expressed the opinion that their observations of changes in field-strength do not agree with what is to be expected according to the theory which I have propounded. This opinion is most strongly expressed in the paper by Schonland and Craib, where it is stated (p. 242): “Such a predominance of the positive type suggests that Simpson’s theory of the production of the charge by the breaking up of large water-drops in an ascending air current, which would produce a cloud of negative polarity, must either be rejected or radically altered.” On the other hand, the data on which these criticisms are based, together with the further knowledge of the meteorological conditions in thunderstorms which has recently been attained, provide the means of completing the details of the theory which were lacking in 1909, and it is now possible to describe the complete mechanism of a thunderstorm both qualitatively and quantitatively. This is the object of the present paper, in which I hope to be able to show that the criticisms are in error and that the theory completely explains all the observations at present available.