Roles of Surface/Volume Diffusion in the Growth Kinetics of Elementary Spiral Steps on Ice Basal Faces Grown from Water Vapor

We measured velocities V step of lateral displacement of individual elementary steps on an ice basal face, for the first time, by advanced optical microscopy, under various bulk water vapor pressure P H 2 O ∞ . Distances L between adjacent spiral steps exhibited considerable variation under constant P H 2 O ∞ . Hence, we analyzed V step as functions of L and P H 2 O ∞ . Then we found that (1) under a constant P H 2 O ∞, V step decreased with decreasing distances L when L ≤ 15 μm and that V step remained constant when L ≥ 15 μm. We named V step of L ≥ 15 μm (isolated steps) V step int and analyzed dependencies of V step int on P H 2 O ∞ . Then we found that (2) the slope of the V step int vs P H 2 O ∞ plot gradually decreased with increasing P H 2 O ∞ . We proposed a model that took into account both the volume diffusion of water vapor molecules and the surface diffusion of water admolecules on a terrace. Our model could explain result (1) mainly by the competition of adjacent spiral steps for water admolecules diffusing on a terrace but could not explain the result (2) satisfactorily.