THE ELECTRIFICATION OF CLOUD DROPLETS IN NON-PRECIPITATING CUMULI

Abstract

The magnitude and character of the electrification of natural cloud-droplets have been investigated. Measurements of the electric field at the surface of non-precipitating clouds show that, as a whole, they are electrically neutral to a good approximation. New airborne apparatus was designed and built to reveal the detailed electrical distribution by separating the electricity carried by the larger droplets from that on the surrounding small particles or air. Measurements in different types of clouds show that the electric charges carried by the cloud elements are large. In warm swelling cumuli at 4,500 feet, the measurements show the following distribution of charge: a. On large cloud-drops centrifuged out and estimated greater than 10 microns diameter Charge usually positive, approximately +3.8 ? 10?6 e.s.u. cm?3. b. On air and tiny drops collected by ion collector, drops estimated less than 10?2 microns diameter Charge usually negative, approximately ?6.1 ? 10?6 e.s.u. cm?3. c. On small cloud-drops missed by both centrifuge and ion collector, estimated to lie between 10?2 and 10 microns diameter. Charge taken as algebraic sum of items (a) and (b), since electric field measurements show cloud is neutral; +2.3 ? 1O?6 e.s.u. cm?3. From these data, the average charge on each of the larger cloud-droplets was estimated to approximate 32 elementary positive units. The centrifuge and the ion filter of the new cloud-analyzer usually capture charges of opposite sign. The measurements emphasize the fundamental electrical character of natural clouds and suggest their stability may be related to electrification.