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unfrozen ground

soil or rock that does not contain any ice.

unfrozen water content

the amount of unfrozen (liquid) water contained in frozen soil or rock.

uniaxial compression test

a method to determine the short-term strength of rocks; conducted by employing a constant loading rate until failure; the failure load is used to calculate the failure stress; can also be used to determine the elastic constants of rocks (i.e. Young's modulus, Poisson's ratio).

unstable air

air in which static instability prevails; this condition is determined by the vertical gradients of air temperature and humidity.

upper air observation

an observation made in the free atmosphere either directly or indirectly.

upper atmosphere

the general term applied to the atmosphere above the mesopause.

upward freezing

the advance of a freezing front upwards from the permafrost table during annual freezing of the active layer.

valley glacier

a mountain glacier whose flow is confined by valley walls.


instrument used to measure wind direction; also called wind vane.

vapor pressure

the pressure exerted by water vapor molecules in a given volume of air.

vein ice

a comprehensive term for ice of any origin occupying cracks in permafrost.

very close pack ice

pack ice in which the floes are tightly packed but not frozen together, with very little, if any, sea water visible; ice cover practically 10/10th.

very open pack ice

pack ice composed of loose, widely spaced floes; ice cover 1/10th to 3/10th.


precipitation that evaporates before reaching the ground.


a measure of a fluid’s resistance to flow; can be thought of as a measure of fluid friction.


the greatest distance that prominent objects can be seen and identified by unaided, normal eyes.


Tools that provide visual images of data on-the-fly.

volumetric (total) water content

the ratio of the volume of the water and ice in a sample to the volume of the whole sample, expressed as a fraction (or, less commonly, as a percentage).

volumetric heat capacity

the amount of heat required to raise the temperature of a unit volume of a substance by one degree.

volumetric latent heat of fusion

the amount of heat required to melt all the ice (or freeze all the pore water) in a unit volume of soil or rock.

warm front

the forward edge of an advancing warm air mass that is displacing cooler air in its path.

warm low

at a given level in the atmosphere, any low that is generally characterized by warmer air near its center than around its periphery; the opposite of a cold low.

water sky

the dark appearance of the underside of a cloud layer when it is over a surface of open water; it is darker than land sky, and much darker than ice blink or snow blink.

water vapor

water substance in vapor (gaseous) form; one of the most important of all constituents of the atmosphere.

waterbody encircling a palsa

a water-filled depression surrounding a palsa.

watermelon snow

snow with red algae growing on it.

wave ogives

ogives that show some vertical relief on a glacier; usually the dark bands are in the hollows and the light bands are in the ridges; form at the base of steep, narrow ice falls.


the state of the atmosphere, mainly with respect to its effects upon life and human activities; distinguished from climate by focusing on short-term (minutes to about 15 days) variations of the atmosphere state.

weathered ice

glacier ice that has been exposed to sun or warm wind so that the boundaries between ice crystals are partly disintegrated.


the processes of ablation and accumulation which gradually eliminate irregularities in an ice surface.

wedge ice

ice occurring in an ice wedge.

well-bonded permafrost

ice-bearing permafrost in which all the soil particles are held together by ice.


the dominant west-to-east motion of the atmosphere, centered over the middle latitudes (35 to 65 degrees latitude) of both hemispheres.


a condition in which daylight is diffused by multiple reflections between a snow surface and an overcast sky; contrasts vanish, and the observer is unable to distinguish the horizon or any snow surface feature.

World Meteorological Organization

created by the World Meteorological Convention and recognized as a special agency of the United Nations in 1951; the WMO consists of more than 185 member countries; and facilitates international cooperation in all aspects of meteorology.

World Meteorological Organization Program

any scientific project (field experiment, inter-comparison, etc.) internationally performed under the aegis of the World Meteorological Organization.