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United States Department of Agriculture

Agricultural Research Service

Title: Low-Temperature Scanning Electron Microscopy of Artificial Snow

Authors
item Wergin, William
item Erbe, Eric
item Rango, Albert
item Foster, J - NASA/GODDARD SPACE FLIGHT
item Pooley, Christopher

Submitted to: Scanning
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 15, 2005
Publication Date: March 1, 2005
Citation: Wergin, W.P., Erbe, E.R., Rango, A., Foster, J., Pooley, C. 2005. Low temperature scanning electron microscopy of artificial snow. Scanning 27(2):63-64.

Interpretive Summary: Samples of artificial snow were collected in ski areas to determine if there is a resemblance to any naturally occurring snow crystals. Samples were stored in liquid nitrogen and imaged in a low-temperature, scanning electron microscope. When the crystal images were compared to naturally occurring crystals, they were most similar to falling graupel or rimed snow particles and to freeze/melt metamorphosed snow grains that occur in the spring in a snowpack. Because of the time and location of formation, they can be distinguished from naturally occurring crystals. The use of low-temperature, scanning electron microscopy can be used by ski-run operators to determine how effective their artificial snow operations are in lengthening the ski season because of the contrast between artificial and natural snow crystals. Other uses would be government agencies leasing ski runs, allowing them to detect any changes in environmental conditions.

Technical Abstract: Low temperature scanning electron microscopy (LTSEM) has been used to observe and characterize fresh and metamorphosed naturally formed snow crystals1. These crystals form in the atmosphere by a process known as vapor deposition, in which molecules of water vapor (gas) bind to form a crystal (solid). No transitional liquid phase occurs. Atmospheric temperature during crystal formation largely influences the structure of the crystals, which may develop into dendrites, plates, columns needles, or irregular crystals, whereas the time of formation influences their sizes. Once formed, the descending snow crystals may encounter super-cooled cloud droplets. The droplets impact and immediately freeze to the surface of the crystal, which is then referred to as being rimed. Continuation of this process, which is known as accretion, results in a mass of frozen droplets, referred to as graupel. Artificial snow appears as microscopic pellets. The types of snow guns and use of ice nucleating agents, influence the sizes of the pellets and the efficiency of production. Artificial snow, which results from the freezing of a liquid, most closely resembles the natural process of accretion that results in riming and graupel. Because sufficient time for vapor deposition seldom occurs, artificial snow does not exhibit the crystalline shapes found in natural snow.

Last Modified: 12/19/2014
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