The electrification of raindrops

Abstract

The charges and masses of individual raindrops were measured in different conditions of rainfall at two different sites. An apparatus was developed to measure raindrop parameters and display their values in the form of a spot whose vertical and horizontal positions on an oscilloscope screen represent the mass and charge respectively. Photographic records, each of a number of successive spots, were made for periods of between half-a-minute and twenty-five minutes during twenty-four separate periods of rainfall which covered many meteorological conditions between thunderstorms and fine drizzle. The photographic results are analysed in terms of the weather conditions applying at the times of measurement. It is shown that stratus and cumulus clouds produce distinct charge/mass patterns on the exposures, and that these patterns can be related to known factors about the nature of the different clouds. The methods of charge measurement by electrostatic induction, and of mass measurement by registering the impacts of drops- on to a detector plate are described. Suggestions are made for future work and improvements to the equipment.