Researchers at the Beltsville Agricultural Research Center (BARC) in Maryland utilizes the US Department of Agriculture’s Low Temperature Scanning Electron Microscope (LT-SEM) to study snow crystals. Simply put, snow crystals are placed onto copper metal sample plates containing pre-cooled methyl cellulose solution, and within a fraction of a second, they’re put into a reservoir of liquid nitrogen which rapidly cools them to -196°C, fusing them to the plates. Continue reading for more.
Under some atmospheric conditions, forming and descending snow crystals may encounter and pass through atmospheric supercooled cloud droplets. These droplets, which have a diameter of about 10 um, can exist in the unfrozen state down to temperatures near -40 °C. Contact between the snow crystal and the supercooled droplets results in freezing of the liquid droplets onto the surface of the crystals. This process of crystal growth is know as accretion. Crystals that exhibit frozen droplets on their surfaces are referred to as rimed.