Charge generation and separation processes

This paper presents a short overview of our current understanding of the generation of charged particles in different environments and circumstances (e.g. thunderclouds, dust storms, volcanic plumes, rings, and planetary surfaces) and the subsequent spatial separation that leads to the formation of electrical fields. Different mechanisms are involved on various scales, starting from the molecular level, through the single particle (droplet, crystal, solid) and finally the entraining volume (cloud, plume etc.). Encapsulated within a dynamic and turbulent medium, particles need to come into contact and to immediately separate, to be later transported away from each other. In order to explain the observed electrical fields and ensuing lightning or other forms of discharge, these processes need to be extremely effective. The section will briefly review laboratory results and modeling efforts of charge separation and electric field build-up in various planetary settings, and cite the appropriate observations of electrical activity on different planets.