Evaporation and Melting of Ice Crystals: A Laboratory Study

Oraltay, R.G. and Hallett, J., 1989. Evaporation and melting of ice crystals: a laboratory study. Atmos. Res., 24: 169-189. Ice crystals as dendrites, plates or columns, grown from the vapor in a chamber at known temperature and supersaturation, were evaporated and melted under controlled temperature, relative humidity and air velocity. Observations on dendritic crystals were made at a relative humidity between 50 and 90% and temperatures between -6 degrees and +5 degrees C. Only evaporation occurred with relative humidity greater than 70% and ice bulb temperature below -3 degrees C. Ice breakup (10 to 15 pieces per 5 mm crystal) and reattachment of the broken pieces (about half) took place during evaporation at ice bulb temperature above -3 degrees C. Evaporation at relative humidity below 70% caused more frequent ice breakup, about 30 pieces per crystal. Water-shedding and ice-breakup were observed during melting of dendrites at relative humidity below 70%; with increase of relative humidity and ambient air temperature, water-shedding and ice-breakup decreased. Experiments for single columns and plates were performed near 80% relative humidity and temperatures 0 to + 2 degrees C. Neither columns nor plates fragmented during evaporation; melting columns shed only water, while no water-shedding at all took place during melting of plates. These laboratory results are applied to secondary ice crystal production in clouds and the interpretation of the radar bright band.