Related Experiment Videos
Irregular snow crystals: structural features as revealed by low temperature scanning electron microscopy.
William P Wergin1, Albert Rango, James Foster
1Agricultural Research Service, US Department of Agriculture, Beltsville, Maryland 20705, USA.
Scanning
|October 24, 2002
Summary
Irregular snow crystals, previously poorly understood, have been characterized using advanced electron microscopy. These unique hexagonal crystals form in aggregates and undergo atmospheric metamorphosis, sometimes resembling graupel or frost.
Area of Science:
- Crystallography
- Atmospheric Science
- Materials Science
Background:
- Irregular snow crystals have been observed for decades but poorly characterized due to limitations of light microscopy.
- Previous studies only vaguely alluded to their existence and unique morphology.
Purpose of the Study:
- To accurately document the structural features of irregular snow crystals.
- To investigate their physical associations and atmospheric metamorphosis.
- To understand the conditions favoring their formation.
Main Methods:
- Utilized a field-emission scanning electron microscope with a cold stage for high-resolution imaging.
- Documented structural details, particle associations, and signs of metamorphosis.
- Observed crystal morphology, size (60-90 mm across a-axis), and c-axis length relative to diameter.
Main Results:
- Irregular snow crystals are hexagonal, with c-axis rarely exceeding diameter.
- They commonly form aggregates of over 100 crystals with parallel axes, creating columnar structures.
- Evidence of atmospheric metamorphosis was observed, with some aggregates resembling graupel and frost formation also noted.
Conclusions:
- Advanced electron microscopy enables detailed characterization of irregular snow crystals.
- These crystals exhibit unique aggregation and metamorphosis behaviors.
- Terrestrial frost formation can involve these irregular crystals, indicating specific atmospheric conditions.