INITIAL ELECTRIFICATION PROCESSES IN THUNDERSTORMS

Abstract

Thunderstorm-electrification processes that develop in clouds which are everywhere above the freezing temperature have been analyzed. Nearly equal numbers of highly electrified positive and negative raindrops are formed by the association of large numbers of cloud droplets, and these themselves are statistically electrified by ionic diffusion. The observed charges carried by both cloud droplets and rain are therefore a manifestation of the ion pairs produced in the free atmosphere primarily by cosmic rays and radioactivity. The discharge characteristics of nearly equal numbers of oppositely electrified drops are determined for drops falling through an atmosphere wherein the positive and negative ionic conductivities are different. It is found that the differential discharge of highly charged rain falling in such an environment systematically separates positive and negative electricity and establishes a distribution that accounts quantitatively for thunderstorms of low to moderate intensity. Useful expressions are developed for the convected free-charge current density established by the process, The analysis leads to a quantitative description of the principal observed features of thunderstorm electrification.