The existence of the electric potential of liquid water on an ice surface is investigated both theoretically and experimentally. The electric potential produced at the boundary surface between the liquid water and bulk ice is set up by the difference of the proton activation energy between liquid water and ice.
Negative charge is developed on the side of liquid water and positive charge on the side of ice.
The expected value of the potential of liquid water on ice is confirmed by the experiments on specimens of highly purified single crystals of ice. The electric properties of bulk ice have been considered to explain the electric charge generation of graupel pellets and hailstones. In this paper, it is shown that the electric properties at the ice surface were important in explaining the charge generation in thunderstorms, especially the explanation of positively electrified graupel pellets and hailstones. This idea is extended to explain the positive charge of snow crystals in the process of melting.