1. Generally, an extensive area of snow-covered ground or ice, relatively smooth and uniform in appearance and composition. This term is often used to describe such an area in otherwise coarse, mounta
inous, or glacial terrain. 2. In glaciology, a region of permanent snow cover, more specifically applied to the accumulation area of glaciers.
Colloquially an ice crystal, or more commonly an aggregation of many crystals that falls from a cloud. Simple snowflakes (single crystals) exhibit beautiful variety of form, but the symmetrical shapes
reproduced so often in photomicrographs are not found frequently in snowfalls. Broken single crystals, fragments, or clusters of such elements are much more typical of actual snow. Snowflakes made up of clusters of crystals (many thousand or more) or crystal fragments may grow as large as three to four inches in diameter, often building themselves into hollow cones falling point downward. In extremely still air, flakes with diameters as large as 10 inches have been reported.
A major category (the D climates) in W. Köppen's climatic classification, defined by a coldest-month mean temperature of less than -3C (26.6F) and a warmest-month mean temperature of greater than 10C
(50F). The first limit separates it from temperate rainy climates, and the second from tundra climates. It is distinguished from the dry climates by a function of annual temperature and precipitation (see formulas under steppe climate). The outstanding feature of these climates is the cold winters with at least a month of snow-covered ground. These are the coldest of the tree climates. In C. W. Thornthwaite's classifications, this general type of climate would be 1) in the 1931 system, humid or subhumid and microthermal climate, or taiga climate; and 2) in the 1948 system, humid or moist subhumid and microthermal climate.
A rare and beautiful phenomenon in which snow is festooned from trees, fences, etc., in the form of a rope of snow, several feet long and several inches in diameter, formed and sustained by surface te
nsion acting in thin films of water bonding individual crystals. Such garlands form only when the surface temperature is close to the melting point, for only then will the requisite films of slightly supercooled water exist.
An instrument for measuring the vertical depth of snow. The eight-inch rain gauge is adapted for snow measurement by removing the funnel and measuring tube so that snow is collected in the overflow ca
n. The weighing rain gauge is also used for measuring snowfall by removing the funnel portion of the collector. Other instruments used for measuring snow depth include the snow sampler and snow stake.
A layer in the middle or upper troposphere in widespread precipitation in which ice crystals form in small convective cells and fall to lower altitudes.
A layer in the middle or upper troposphere in widespread precipitation in which ice crystals form in small convective cells and fall to lower altitudes. Such layers are thought to be characterized by
convective instability. Small convective cells called generating cells that develop within the layer may produce ice crystals that then settle into lower altitudes. The base of the convectively unstable layer is called the snow-generating level. On time-height displays from vertically pointing radars, generating cells are typically observed to extend about 1-2 km above the snow-generating level. Snow trails, or streamers, are terms used to describe the trails of precipitation that subsequently emerge from the base of the generating cells.