Charge separation in thunderstorm conditions

Abstract

A laboratory investigation of the electric charge transfer in collisions between vapor‐grown ice crystals and a riming target is presented in this work. A series of experiments were conducted for ambient temperatures between −8°C and −29°C, air velocity of 8 m s−1, and effective liquid water content from 0.5 to 10 g m−3, with the goal of studying the performance of the noninductive mechanism under a wide range of temperature and liquid water content. At low temperatures (below −19°C), the results revealed no dependence of the charge separated per collision upon variations of the liquid water content. While at temperatures above −19°C, the efficiency of the graupel charging could decrease as the liquid water content increases, as a consequence of the decrease of the probability that the ice crystals impact and rebound from the graupel surface in the dry growth regime. We found that the dominant sign of the graupel charging was negative for temperatures below −15°C and positive at higher temperatures. A simple functional representation of our laboratory results is given so that they can be incorporated in cloud electrification models.