page_title: Snow
section_title: Measurement and classification
hierarchical_section_title: Snow / Science / Measurement and classification
caption_attribution_description: English: A scientist collecting snow and ice samples from the wall of a snow pit. Fresh snow can be seen at the surface and en:glacier ice at the bottom of the pit wall. The snow layers are composed of progressively denser en:firn. Taku Glacier, Juneau Icefield, en:Tongass National Forest, en:Alaska. http://pubs.usgs.gov/of/2004/1216/f/images/firn1.gif Contents 1 Automatically converted to PNG 1.1 Previous file history 1.2 Previous description history 2 Licensing 3 Original upload log Automatically converted to PNG The PNG crusade bot automatically converted this image to the more efficient PNG format. The image was previously uploaded as "Taku glacier firn ice sampling.gif". Previous file history 02:39:49, 13 May 2005 (UTC) . . SEWilco (Talk | Contribs) . . 519x352 (110,929 bytes) (A scientist collecting snow and ice samples from the wall of a snow pit. Fresh snow can be seen at the surface and en:glacier ice at the bottom of the pit wall. The snow layers are composed of progressively denser en:firn. Taku Glacier, Juneau Icefield,) Previous description history 18:59:07, 21 April 2007 (UTC) Remember the dot (Talk | Contribs) ({{ShouldBePNG}}) 02:41:13, 13 May 2005 (UTC) SEWilco (Talk | Contribs) (wk) 02:39:49, 13 May 2005 (UTC) SEWilco (Talk | Contribs) (A scientist collecting snow and ice samples from the wall of a snow pit. Fresh snow can be seen at the surface and en:glacier ice at the bottom of the pit wall. The snow layers are composed of progressively denser en:firn. Taku Glacier, Juneau Icefield,)
context_page_description: Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water throughout its life cycle, starting when, under suitable conditions, the ice crystals form in the atmosphere, increase to millimeter size, precipitate and accumulate on surfaces, then metamorphose in place, and ultimately melt, slide or sublimate away.
  Snowstorms organize and develop by feeding on sources of atmospheric moisture and cold air. Snowflakes nucleate around particles in the atmosphere by attracting supercooled water droplets, which freeze in hexagonal-shaped crystals. Snowflakes take on a variety of shapes, basic among these are platelets, needles, columns and rime. As snow accumulates into a snowpack, it may blow into drifts. Over time, accumulated snow metamorphoses, by sintering, sublimation and freeze-thaw. Where the climate is cold enough for year-to-year accumulation, a glacier may form. Otherwise, snow typically melts seasonally, causing runoff into streams and rivers and recharging groundwater.
context_section_description: In the field snow scientists often excavate a snow pit within which to make basic measurements and observations. Observations can describe features caused by wind, water percolation, or snow unloading from trees. Water percolation into a snowpack can create flow fingers and ponding or flow along capillary barriers, which can refreeze into horizontal and vertical solid ice formations within the snowpack. Among the measurements of the properties of snowpacks that the International Classification for Seasonal Snow on the Ground includes are: snow height, snow water equivalent, snow strength, and extent of snow cover. Each has a designation with code and detailed description. The classification extends the prior classifications of Nakaya and his successors to related types of precipitation and are quoted in the following table:
  All are formed in cloud, except for rime, which forms on objects exposed to supercooled moisture.
  It also has a more extensive classification of deposited snow than those that pertain to airborne snow. The categories include both natural and man-made snow types, descriptions of snow crystals as they metamorphose and melt, the development of hoar frost in the snow pack and the formation of ice therein. Each such layer of a snowpack differs from the adjacent layers by one or more characteristics that describe its microstructure or density, which together define the snow type, and other physical properties. Thus, at any one time, the type and state of the snow forming a layer have to be defined because its physical and mechanical properties depend on them. Physical properties include microstructure, grain size and shape, snow density, liquid water content, and temperature.
caption: Snow pit on the surface of a glacier, profiling snow properties where the snow becomes increasingly dense with depth as it metamorphoses towards ice
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