Ice crystals are solid ice exhibiting atomic ordering on various length scales and include hexagonal columns, hexagonal plates, dendritic crystals, and diamond dust. The highly symmetric shapes are due to depositional growth, namely, direct deposition of water vapour onto the ice crystal. Depending on environmental temperature and humidity, ice crystals can develop from the initial hexagonal prism into numerous symmetric shapes. Possible shapes for ice crystals are columns, needles, plates and dendrites. If the crystal migrates into regions with different environmental conditions, the growth pattern may change, and the final crystal may show mixed patterns. An example are capped columns. Ice crystals tend to fall with their major axis aligned along the horizontal, and are thus visible in polarimetric weather radar signatures with enhanced (positive) differential reflectivity values. Electrification of ice crystals can induce alignments different from the horizontal. Electrified ice crystals are also well detectable by polarimetric weather radars.
Temperature and water vapor humidity determine crystalline forms. Ice crystals are responsible for various atmospheric optics displays.
Ice clouds are composed of ice crystals, the most notable being cirrus clouds and ice fog. The slight whitening of a clear blue sky caused by ice crystals high in the troposphere can be a sign that a weather front (and rain) is approaching, as moist air is carried to high levels and freezes to ice crystals.
Read more about Ice Crystals: Geometry
Famous quotes containing the words ice and/or crystals:
“He was high and mighty. But the kindest creature to his slaves—and the unfortunate results of his bad ways were not sold, had not to jump over ice blocks. They were kept in full view and provided for handsomely in his will. His wife and daughters in the might of their purity and innocence are supposed never to dream of what is as plain before their eyes as the sunlight, and they play their parts of unsuspecting angels to the letter.”
—Anonymous Antebellum Confederate Women. Previously quoted by Mary Boykin Chesnut in Mary Chesnut’s Civil War, edited by C. Vann Woodward (1981)
“It is clear that everybody interested in science must be interested in world 3 objects. A physical scientist, to start with, may be interested mainly in world 1 objects—say crystals and X-rays. But very soon he must realize how much depends on our interpretation of the facts, that is, on our theories, and so on world 3 objects. Similarly, a historian of science, or a philosopher interested in science must be largely a student of world 3 objects.”
—Karl Popper (1902–1994)