Estimating Surface Attachment Kinetic and Growth Transition Influences on Vapor-Grown Ice Crystals

There are few measurements of the vapor growth of small ice crystals at temperatures below -30 degrees C. Presented here are mass-growth measurements of heterogeneously and homogeneously frozen ice particles grown within an electrodynamic levitation diffusion chamber at temperatures between -44 degrees and -30 degrees C and supersaturations s(i) between 3% and 29%. These growth data are analyzed with two methods devised to estimate the deposition coefficient alpha without the direct use of s(i). Measurements of s(i) are typically uncertain, which has called past estimates of a into question. We find that the deposition coefficient ranges from 0.002 to unity and is scattered with temperature, as shown in prior measurements. The data collectively also show a relationship between alpha and s(i), with alpha rising (falling) with increasing s(i) for homogeneously (heterogeneously) frozen ice. Analysis of the normalized mass growth rates reveals that heterogeneously frozen crystals grow near the maximum rate at low s(i), but show increasingly inhibited (low alpha) growth at high s(i). Additionally, 7 of the 17 homogeneously frozen crystals cannot be modeled with faceted growth theory or constant alpha. These cases require the growth mode to transition from efficient to inefficient in time, leading to a large decline in alpha. Such transitions may be, in part, responsible for the inconsistency in prior measurements of alpha.