Toward a Comprehensive Model of Snow Crystal Growth: 9. Characterizing Structure-Dependent Attachment Kinetics near -4 C

TL;DR

This paper investigates snow crystal growth near -4 C, demonstrating that structure-dependent attachment kinetics (SDAK) significantly influence morphology, supported by experimental data and explaining transitions in crystal shapes.

Contribution

It provides a comprehensive model incorporating SDAK effects near -4 C, revealing a common physical mechanism behind different temperature-dependent growth behaviors.

Findings

SDAK dips are supported by experimental data near -4 C and -14 C.

Edge surface diffusion reduces nucleation barriers on narrow facets.

The model explains morphological transitions in snow crystals observed in nature.

Abstract

In this paper I examine snow crystal growth near -4 C in comparison with a comprehensive model that includes Structure-Dependent Attachment Kinetics (SDAK). Together with the previous paper in this series that investigated growth near 14 C, I show that a substantial body of experimental data now supports the existence of pronounced 'SDAK dips' on basal surfaces near -4 C and on prism surfaces near -14 C. In both cases, the model suggests that edge-associated surface diffusion greatly reduces the nucleation barrier on narrow facet surfaces relative to that found on broad facets. The remarkable quantitative similarities in the growth behaviors near -4 C and -14 C suggest that these two SDAK features arise from essentially the same physical mechanism occurring at different temperatures on the two principal facets. When applied to atmospheric snow crystal formation, this comprehensive model can explain the recurrent morphological transitions between platelike and columnar growth seen in the Nakaya diagram.