Ice particle generation during evaporation

Abstract

Simulated soft hail (graupel) particles are grown in a laboratory chamber and evaporated under controlled conditions of wind speed, temperature and undersaturation. Particle breakup is observed directly and recorded by video, and also inferred from abrupt changes of charge. A particle with a diameter of a few mm may give rise to several hundred particles under some conditions. Breakup occurs by irregular evaporation of the rime branches, which thin to less than 10 μm prior to fracture. Break up is also observed during evaporation of individual faceted vapor grown crystals. All ice particles are strong; the fracture strength is estimated to be at least ten times the bulk fracture strength of ice.