Crystal Structure of Ice Accreted on an Ice Substrate

Abstract

Abstract Thin ice deposits, grown on a prismatic ice substrate and the first layers of large deposits grown about a cylindrical ice collector, are studied. Experiments were performed at 30 m s–1 wind speed and T a near –20° C. Progressive structural changes in thin accretions with time of water-injection were observed, when the substrate temperature was Ts > –5°C. After 60s injection, which determined a deposit ~1 mm thick, the preferred orientation was established and the mean grain area was ~0.01 mm2. Such structural changes did not appear along the initial layers of thick deposits. These differed mainly from the subsequent zone because of the larger value of the preferred angle between the c-axis and the growth direction. These effects are discussed by considering the nucleation and orientation selection processes which occurred during droplet freezing and the annealing effects that occurred below the growth front. The different c-axis orientations in the initial and main zones are related to the different Ts values during their formation.