Ice particle generation during evaporation

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 mu m 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.