Abstract
Clear sky ice crystals or diamond dust displays are observed in polar regions, both remote and populated; when the temperature falls to −20°C and where abundant sources of water vapor are present. In remote areas of the Arctic, these ice crystals are confined to the lowest 1000 m, leeward of open leads in the sea ice. The crystals always occur in air between ice and water saturation, and air dryer than ice saturation normally overlies the display. In populated regions, water vapor is supplied from man-made sources such as heating plants. Morphological studies of these ice crystals suggest that they are formed first by condensation into water droplets and then by freezing.
