Chlorides in Natural and Artificial Hailstones

Abstract

A membrane filter technique for precisely locating chlorides on any prepared ice surface has been tested on hailstone cross sections. Chloride patterns, different in intensity in the various growth stages of the hailstones, were detected along the grain boundaries. To relate the environmental growth conditions of the hailstones to the chloride distributions, the filter technique has been applied to deposits of ice grown by accretion in a wind tunnel from droplets of known NaCl concentrations. The results show a dependence of the chloride distributions on time and temperature of storage: initially chlorides are uniformly distributed in the lattice structure and subsequently segregate to the grain boundaries during storage at temperatures close to 0°C.It is suggested that the technique, especially when performed on freshly fallen hailstones, may contribute in inferring growth conditions of the hailstones in the parent cloud and their trajectories, provided that a realistic model of the chloride concentration in the liquid water of the hailcloud is outlined.