|Title||Rime and graupel: Description and characterization as revealed by low temperature scanning electron microscopy|
|Publication Type||Journal Article|
|Year of Publication||2003|
|Authors||Rango A., Foster J., Josberger E.G., Erbe E.F., Pooley C.D., Wergin W.P.|
|Date Published||May 1, 2003|
|ARIS Log Number||142593|
For nearly 100 years, investigators using light microscopy have vaguely alluded to unique types of snow crystals known as rime and graupel. However, the limited resolution and depth of field of the light microscope have prevented investigators from characterizing these crystals. In this study, a field emission scanning electron microscope equipped with a cold stage was used to document the structural features, physical associations and atmospheric metamorphosis of rime and graupel snow crystals. Rime and graupel form in clouds having both snow crystals and super cooled cloud droplets. This study shows that the frozen droplets range from 10-50um in diameter. With the low temperature scanning electron microscopy approach, it is possible to distinguish the original snow crystal types until the accretion of droplets become thick enough to obscure the original crystal and graupel is the result. With continued riming, lump graupel can reach a diameter of 1-3mm. This study confirms the light microscopy conclusion that the structure of graupel includes considerable air spaces. The low temperature electron microscope approach is the only method that allows measurement of the accreted cloud droplets on rimed crystals and graupel.