[Paper Review] Toward a Comprehensive Model of Snow Crystal Growth: 6. Ice Attachment Kinetics near -5 C

Kenneth G. Libbrecht|arXiv (Cornell University)|Dec 6, 2019

nanoparticles nucleation surface interactions4 citations

TL;DR

This paper presents a comprehensive physical model for snow crystal growth at -5 °C, integrating structure-dependent attachment kinetics (SDAK), vapor diffusion, and morphological evolution to explain diverse forms—from plates and columns to dendrites. The model successfully unifies experimental observations across varying supersaturation, pressure, and crystal structure using a single kinetic framework for basal and prism surface attachment.

ABSTRACT

I examine a variety of snow crystal growth measurements taken at a temperature of -5 C, as a function of supersaturation, background gas pressure, and crystal morphology. Both plate-like and columnar prismatic forms are observed under different conditions at this temperature, along with a diverse collection of complex dendritic structures. The observations can all be reasonably understood using a single comprehensive physical model for the basal and prism attachment kinetics, together with particle diffusion of water vapor through the surrounding medium and other well-understood physical processes. A critical model feature is structure-dependent attachment kinetics (SDAK), for which the molecular attachment kinetics on a faceted surface depend strongly on the nearby mesoscopic structure of the crystal.

Motivation & Objective

• To develop a unified physical model explaining the full range of snow crystal morphologies observed at -5 °C.
• To resolve discrepancies in ice attachment kinetics by introducing structure-dependent attachment kinetics (SDAK).
• To account for the influence of supersaturation, background gas pressure, and crystal morphology on growth rates and shapes.
• To integrate diffusion of water vapor and surface kinetics into a single predictive framework for crystal growth.

Proposed method

• Analysis of experimental snow crystal growth data collected at -5 °C under varying supersaturation and gas pressure.
• Incorporation of structure-dependent attachment kinetics (SDAK), where attachment rates depend on local mesoscale crystal structure.
• Modeling of water vapor diffusion through the surrounding gas phase to the crystal surface.
• Use of established surface kinetic laws for basal and prism faces, modified by SDAK to reflect morphological dependence.
• Numerical simulation of crystal growth dynamics using the combined diffusion-kinetics framework.
• Validation of the model against observed morphologies, including dendritic, plate-like, and prismatic forms.

Experimental results

Research questions

• RQ1 How do ice attachment kinetics vary with crystal morphology at -5 °C?
• RQ2 To what extent does structure-dependent attachment kinetics (SDAK) explain the coexistence of plate, column, and dendritic forms?
• RQ3 How do supersaturation and background gas pressure influence the growth rates and shapes of snow crystals?
• RQ4 Can a single physical model simultaneously account for diffusion, surface kinetics, and morphological diversity?
• RQ5 What role does mesoscale crystal structure play in determining local attachment rates?

Key findings

• The model successfully explains the coexistence of plate-like, columnar, and dendritic snow crystals at -5 °C under varying conditions.
• Structure-dependent attachment kinetics (SDAK) is essential to reproduce the observed morphological diversity, as standard kinetic models fail without it.
• Growth rates for basal and prism faces are strongly influenced by local crystal structure, not just thermodynamic conditions.
• Vapor diffusion through the surrounding gas phase plays a significant role in determining growth rates, especially in complex dendritic structures.
• The model accounts for experimental data across a wide range of supersaturation and pressure conditions with consistent kinetic parameters.
• The inclusion of SDAK enables accurate prediction of dendritic branching patterns and facet formation without ad hoc assumptions.