The structure and stability of ball lightning

Abstract

The main characteristics of ball lightning are well established. They include its general appearance (shape, size range, brightness, etc.), its peculiar motion and, less satisfactorily, its energy content. A remarkably consistent picture emerges from the thousands of detailed descriptions which are now available. There is, however, no such consistency in the various hypotheses that have been put forward to explain ball lightning. The only thing most of them share is an ability to explain a few aspects of the phenomenon at the expense of physically impossible requirements in other areas. If one is to accept that a single phenomenon is being described in all these observations, it seems clear that ball lightning is, at the very least, an electrical and chemical phenomenon; and several branches of both disciplines seem to be involved. High humidities are nearly always implied and it is known that the behaviour of strong electrolytes in saturated water vapour cannot be properly modelled thermodynamically. An approximate way of circumventing this problem is developed. It allows a thorough, if only approximate, thermodynamic analysis to be undertaken From this, phenomena that explain the structure and stability of ball lightning are predictable. They arise quite naturally by considering the nature, energetics and fate of ions escaping from a hot air plasma into the cool, high humidity environment of electrically charged air. The model resulting is as follows. A central plasma core is surrounded by a coo er, intermediate zone, in which recombination of most or all of the high-energy ions takes place. Further out is a zone in which temperatures are low enough for any ions present to become extensively hydrated. Hydrated ions can also form spontaneously in the inner, hotter, parts of this hydration zone. Near the surface of the ball is a region, quite essential to the model, in which thermochemical refrigeration can take place. In an established ball, energy is supplied not only by electric fields and, possibly, electromagnetic fields, but also by the production of nitric acid from nitrogen and oxygen and by the hydration of the ions. It is shown that, if NO - 2 and H 3 O + ions become hydrated by more than about five water molecules before they can combine at the edge of the ball, the reaction will be endothermic and can refrigerate its surface. The ball can thus be considered as a thermochemical heat pump powered by the electric field of a thunder storm. The surface refrigeration allows the condensation of water in quantities sufficient to counteract the buoyancy of the hot plasma. The in-flow of N 2 and O 2 produces both nitrous and nitric acids, the latter being dissolved in the water droplets. The flow of gas inwards past these droplets (and past those condensed around an excess of H 3 O + ions) provides an effective surface tension for the ball which appears sufficient to explain its shape and mechanical stability. Clearly explanations for the surface coolness and frequently reported cloudiness are provided at the same time. All the well documented properties (amounting to over 20 distinct properties in total) can be explained in a consistent manner within the framework of the model.