Observations of the morphology and sublimation-induced changes in uncoated snow using scanning electron microscopy

The morphology of a fresh-snow specimen and the sublimation-induced structural changes in an individual snow crystal were examined using a high-vacuum scanning electron microscope (SEM) equipped with a cryo system. The snow specimen was collected during a snowfall in Hanover, NH, USA, and was initially maintained at liquid nitrogen temperature in order to prevent any structural changes. Without coating, snow crystals can sublimate in the SEM chamber at a rate that is mainly determined by the temperature of the specimen. After the initial morphology was examined at similar to 180 degrees C, sublimation was initiated by slowly increasing the stage temperature, and changes in morphology were recorded by taking images of an individual snow crystal intermittently and recording the temperatures and times. Severe morphological destructions due to sublimation occurred at around similar to 150 degrees C. This approach allowed us to closely observe both the initial morphology and the structural changes in snow crystals as they underwent sublimation, a significant process during snow metamorphism. These observations also serve as a reference for temperature selection in the study of uncoated snow with a similar morphology using a high-vacuum SEM. Copyright (C) 2010 John Wiley & Sons, Ltd.