Influences of Lateral Facet Spreading on Vapor Depositional Growth Rates of Ice Crystals

Abstract:

The vapor-growth of small ice particles (radius < 50 µm) is critical for the development and persistence of cirrus clouds. Theories on the growth of these particles typically focus on the normal growth of facets, where mass added to a facet increases the length of the semi-axis normal to that facet. However, facets may also experience lateral growth as they spread across the crystal surface, increasing the crystal’s mass, volume, and surface area, but not its maximum dimension. Though lateral growth should be expected to occur as a frozen droplet grows into a faceted crystal, it has not been widely studied. Presented here are measurements of the vapor mass growth of homogeneously frozen ice particles in a levitation diffusion chamber at temperatures between -36 and -65 °C. We compare these data to a new model of lateral facet spreading. While many of the measured growth rates can be described by normal growth alone, some data require the lateral spreading model to simulate the beginning, or even the entirety, of the growth period.