A charge emitter for use in evaluating aircraft rainfall enhancement

Abstract

Charging of droplets is known to influence their properties and interactions, such as through modifying their evaporation, collisions or stability. Introducing additional charge into a droplet system, such as a natural fog or cloud may therefore provide a route to modify its behaviour. As aircraft are already used in rainfall enhancement activities by some national meteorological services, adapting their existing delivery systems to include charge release provides a convenient method with which to pursue this. Rainfall enhancement aircraft typically carry an array of under-wing tubes into which cloud seeding agents (e.g. salt or silver iodide) are contained in flares which are loaded pre-flight. Our approach for a charge release system is to construct a stand-alone device able to fit within an existing flare housing, to provide controlled release of ions by corona emission. The “flare emitter” device is battery powered and able to release either polarity of corona ions. It contains a programmable microcontroller (Arduino Nano) able to operate in a fixed sequence and record data to an internal memory card at 10Hz. Monitoring systems for the corona emission voltage and current are included, as well as environmental sensors for pressure, temperature and relative humidity.