Scanning electron microscopy and molecular dynamics of surfaces of growing and ablating hexagonal ice crystals W. C. Pfalzgraff, R. M. Hulscher, and S. P. Neshyba University of Puget Sound, Tacoma, Washington, 98416, USA
Abstract. We present the first clearly resolved observations of
surfaces of growing and ablating hexagonal ice crystals using
variable-pressure scanning electron microscopy. The ice surface develops
trans-prismatic strands, separated from one another by distances of 5–10 μm.
The strands are present at a wide range of supersaturations, but
are most pronounced at temperatures near the frost point. Pyramidal facets
consistent with Miller-Bravais indices of 1011, and possibly also 2021,
are associated with ice growth under these conditions. A
molecular-dynamics model of a free-standing ice Ih nanocolumn containing
8400 water molecules does not develop trans-prismatic strands, suggesting
these features originate at larger spatial or temporal scales. The possible
relevance of these surface features to cirrus ice is discussed.
Citation: Pfalzgraff, W. C., Hulscher, R. M., and Neshyba, S. P.: Scanning electron microscopy and molecular dynamics of surfaces of growing and ablating hexagonal ice crystals, Atmos. Chem. Phys., 10, 2927-2935, doi:10.5194/acp-10-2927-2010, 2010.