Mesoscopic surface roughness of ice crystals pervasive across a wide range of ice crystal conditions

Abstract

Abstract. Here we show high-magnification images of hexagonal ice crystals acquired by Environmental Scanning Electron Microscopy (ESEM). Most ice crystals were grown and sublimated in the water vapor environment of an FEI-Quanta-200 ESEM, but crystals grown in a laboratory diffusion chamber were also transferred intact and imaged via ESEM. All of these images display prominent mesoscopic topography including linear striations, ridges, islands, steps, peaks, pits, and crevasses; the roughness is not observed to be confined to prism facets. The observations represent the most highly magnified images of ice surfaces yet reported and expand the range of conditions where the rough surface features are known to be conspicuous. Microscale surface topography is seen to be ubiquitously present at temperatures ranging from −10 °C to −40 °C, at super-saturated and sub-saturated conditions, on all crystal facets, and irrespective of substrate. Despite the constant presence of surface roughness, the patterns of roughness are observed to be dramatically different between growing and sublimating crystals, and transferred crystals also display qualitatively different patterns of roughness. Crystals are also demonstrated to sometimes exhibit inhibited growth in moderately supersaturated conditions following exposure to near-equilibrium conditions, a phenomena interpreted as evidence of 2-D nucleation. New knowledge of the characteristics of these features could affect the fundamental understanding of ice surfaces and their physical parameterization in the context of satellite retrievals and cloud modeling. Links to Supplement videos of ice growth and sublimation are provided.

Ice particle morphology and microphysical properties of cirrus clouds inferred from combined CALIOP‐IIR measurements

“…In consequence, the HOP fraction is ∼ 0.01%, which is significantly smaller than measured by previous studies Chepfer, 2004, 2010]. Several papers have reported that surface texture of ice crystals may not be perfectly smooth [Magee et al, 2014], although a smooth surface is assumed in the hexagonal plates in this study due to limitation of PGOH computation. HOPs with a roughened surface may provide weaker backscattering intensity and higher depolarization ratio than those with a smooth surface, and therefore, this study could underestimate the plate and HOP fraction if clouds contain roughened plate particles.…”

Captured Cirrus Ice Particles in High Definition

“…3 panels, and Supplement 1). These observations of roughening are quite similar to those observed for ice particles grown within environmental SEM (Magee et al 2014;Pfalzgraff et al 2010;Neshyba et al 2013, Butterfield et al 2017 as well a new experimental growth chamber built specifically to investigate ice surface roughening (Voigtländer et al 2018). These observations of roughness at amplitudes and patterning agree with in-situ reports of multi-scale roughness by Collier et al 2016.…”

Quantitative three‐dimensional ice roughness from scanning electron microscopy

“…Indeed, recent years have seen considerable progress along these lines. In particular, investigations using scanning electron microscopy have shown that roughness can span multiple spatial scales [ Neshyba et al ., ; Magee et al ., ] and can be distinctly azimuthally anisotropic [ Pfalzgraff et al ., ].…”