Surface potentials of ice and thunderstorm charge separation

There is no general agreement on the nature of the mechanism which causes thunderstorms to become electrified 1,2 . Many scientists believe that charge is transferred when ice crystals collide with hailstones, and that subsequent gravitational separation results in field growth to breakdown magnitudes. Buser and Auf dermaur 3 have proposed that the charging results from differences in the surface potential of ice. The measurements described here suggest that the surface potential of polycrystalline ice, such as would occur in a thunderstorm, is related simply to its past growth history. The sudden step in potential postulated by Buser and Aufdermaur as the ice surface changes from an evaporating to a growing state could not be detected. However, a natural hailstone grows by riming as it collects supercooled droplets, and these new measurements suggest that this effect results in much larger changes in surface potential.