A possible mechanism of ice splinter production during riming

Abstract

IN supercooled clouds of particular characteristics—notably a broad droplet size distribution—the concentrations of ice particles at a given level may exceed by several orders of magnitude the measured concentrations of ice nuclei.1–3 These observations have important implications with respect to the efficacy of techniques for the artificial anhancement of rainfall. There is good evidence4,5 supported by calculations6,7 that the secondary ice particles form during the process of riming. However, the physical mechanisms by which these particles are produced has not been identified. We describe here some experiments which suggest that the bursting of supercooled droplets as they freeze onto a riming ice particle may be responsible. This fragmentation process is well established for isolated drops in air, which may lose heat more-or-less symmetrically to their environment as they freeze, thus permitting the formation of a closed shell of ice within which immense pressures may develop as freezing proceeds. However, no generally accepted evidence exists for the occurrance of this process during the growth of rime.