Articles | Volume 14, issue 22
Atmos. Chem. Phys., 14, 12357–12371, 2014
Atmos. Chem. Phys., 14, 12357–12371, 2014

Research article 25 Nov 2014

Research article | 25 Nov 2014

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

N. B. Magee, A. Miller, M. Amaral, and A. Cumiskey N. B. Magee et al.
  • The College of New Jersey, Ewing, NJ, USA

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 in which 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, in supersaturated and subsaturated 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 phenomenon interpreted as evidence of 2-D nucleation. New knowledge about 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 supplemental videos of ice growth and sublimation are provided.

Short summary
High-resolution images of ice crystals acquired by environmental scanning electron microscope reveal a wide array of surface complexities at scales from 100 nm to greater than 10 microns. These observations include ice crystals grown in the low-pressure microscope chamber and crystals grown externally under cirrus cloud conditions and then transferred for imaging. The results suggest that accounting for microscale complexity is critical for understanding cirrus interactions with radiation.
Final-revised paper