Submitted to: Journal of Microscopy Society America
Publication Type: Proceedings
Publication Acceptance Date: June 20, 1996
Publication Date: N/A
Interpretive Summary: Winter precipitation provides advantages and disadvantages for the US consumer. On one hand, 1/3 of the water used for irrigating crops and producing hydroelectric power is provided by snow. Alternatively, precipitation such as ice and sleet are hazardous to ground and air transportation. Methods currently used for calculating the amount of water in snow are inaccurate resulting in multimillion dollar losses in agricultural efficiency. Current technology does not permit detailed studies of icing on airplanes and runways. To overcome these problems ARS scientists have developed a method for examining winter snow and ice with an instrument called a scanning electron microscope. With this method, snow, ice and frost can be collected and examined in the laboratory to reveal information about the basic shapes, sizes and growth of crystals. This information will be used by scientists to improve modeling systems that predict the amount of water in snowpack and benefit farmers who require irrigation water. It will also help scientists understand how ice layers develop and how they can be prevented or reduced.
Technical Abstract: Low temperature scanning electron microscopy was used to observe icicles, ice fabric, rime and frost. Icicles were collected at Beltsville, MD; snow crystals, ice fabric and frost were collected from sites at Bearden Mountain, WV. The samples were collected on flat copper plates, rapidly plunged into LN2 and lowered into a LN2 storage dewar where they remained until they were sputter coated for observation with low temperature SEM. Small forming icicles revealed concentric rings of air bubbles that may be released and entrapped as successive layers of water freeze. Compressed snow flattened the surface of the snowpack and caused fragmentation and compaction of crystals that could be readily characterized as ice fabric. The rime could be imaged on the surfaces of precipitating crystals. The frost consisted of needles that presumably formed from the condensation of water vapor. These results suggest that low temperature SEM is useful for imaging frozen aqueous specimens that could also include ice core samples and particulate pollutants that become incorporated into snow and ice. In addition, this technique could be used to image such dynamic phenomenon as icing on the surface of aircraft wings.