Use of low-temperature scanning electron Microscopy to compare and characterize three classes of snow cover

TitleUse of low-temperature scanning electron Microscopy to compare and characterize three classes of snow cover
Publication TypeJournal Article
Year of Publication2006
AuthorsFoster J., Kelly R., Rango A., Armstrong R., Erbe E.F., Pooley C.D., Wergin W.P
Date Published12/2006
ARIS Log Number197354
Keywordsdepth hoar, low temperature scanning electron, snow cover, snow crystal

This study, which uses low temperature scanning electron microscopy (LTSEM), systematically sampled and characterized snow crystals that were collected from three unique classes of snow cover: prairie, taiga and alpine. These classes, which were defined in previous field studies, result from exposure to unique climatic variables relating to wind, precipitation and air temperature. Snow samples were taken at 10 cm depth intervals from the walls of freshly excavated snow pits. The depth of the snow pits for the prairie, taiga and alpine covers were 28 cm, 81 cm and 110 cm, respectively. Visual examination revealed that the prairie snow cover consisted of two distinct layers whereas the taiga and alpine covers had four distinct layers. Visual measurements were able to establish the range of crystal sizes that occurred in each layer, the temperature within the pit and the snow density. The LTSEM observations revealed the detailed structures of the types of crystals that occurred in the snow covers and documented the metamorphosis that transpired in the descending layers. Briefly, the top layers from two of the snow covers, consisted of freshly fallen snow crystals that could be readily distinguished as plates and columns (prairie) or graupel (taiga). Alternatively, the top layer in the alpine cover consisted of older dendritic crystal fragments that had undergone early metamorphosis, i.e. they had lost their sharp edges and had begun to show signs of joining or bonding with neighboring crystals. A unique layer, known as sun crust, was found in the prairie snow cover; however, successive samplings from all three snow covers showed similar stages of metamorphism that led to the formation of depth hoar crystals. These changes included the gradual development of large, three-dimensional crystals having clearly defined flat faces, sharp edges, internal depressions and facets. The study, which indicates that LTSEM can be used to enhance visual data by systematically characterizing snow crystals that are collected at remote locations, is important for understanding the physics of snowpacks and the metamorphosis that leads to potential avalanche situations. In addition, the metamorphosis of snow crystals must be considered when microwave radiometry is used to estimate the snow water equivalent in the winter snowpack, because large snow crystals more effectively scatter passive microwave radiation than small crystals. http://