CHARGE SEPARATION BY ICE AND WATER DROPS DURING GROWTH AND EVAPORATION

Experiments reveal complicated charging behavior during evaporation and vapor growth of ice and water in air. In the laboratory environment, the ice specimen acquires a positive charge during growth and a negative charge during evaporation, except in the temperature region between -4-degrees-C and 0-degrees-C, where ice behaves like water, acquiring a negative charge during condensation growth. The current is in excess of 10(-16) amps cm-2 s-1. The ion concentration in the air has a strong effect on the charging direction. The analysis shows that the charging direction is not simply the result of evaporation or growth as suggested in earlier work but is determined by the properties of the charge carriers in ice (or water) and in the air. The new hypothesis can explain the charging behavior of both the growth of ice and water from the vapor and also evaporation observed in the present experiments. This new hypothesis also gives interpretation of some discrepancies in the earlier studies. The mechanism does not require absolute growth or evaporation to operate, and it is possibly an important contributory factor in charge separation both in thunderstorms and weakly electrified clouds when long growth or evaporation times are available.