Raindrop charge-size measurements in warm rain

Abstract

Measurements were made of size and electric charge of raindrops falling from warm clouds at Hilo, on the windward coast of the island of Hawaii, during November and December 1970. Most raindrops smaller than 1.4 mm in diameter are negatively charged, whereas larger drops are predominantly positive. Rainfall from shallow cumulus clouds most frequently contains negatively charged raindrops. A tentative model is proposed to explain the observed variation in raindrop size and charge during the development of warm clouds over Hawaii.