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unfrozen ground

soil or rock that does not contain any ice.
Topic: 
frozen ground or permafrost

unfrozen water content

the amount of unfrozen (liquid) water contained in frozen soil or rock.
Topic: 
frozen ground or permafrost

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).
Topic: 
frozen ground or permafrost

unstable air

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

Topic: 
climatology and meteorology

upper air observation

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

Topic: 
climatology and meteorology

upper atmosphere

the general term applied to the atmosphere above the mesopause.

Topic: 
climatology and meteorology

upward freezing

the advance of a freezing front upwards from the permafrost table during annual freezing of the active layer.
Topic: 
frozen ground or permafrost

valley glacier

a mountain glacier whose flow is confined by valley walls.
Topic: 
glaciers

vane

instrument used to measure wind direction; also called wind vane.
Topic: 
climatology and meteorology

vapor pressure

the pressure exerted by water vapor molecules in a given volume of air.
Topic: 
climatology and meteorology

vein ice

a comprehensive term for ice of any origin occupying cracks in permafrost.
Topic: 
frozen ground or 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.
Topic: 
sea ice

very open pack ice

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

virga

precipitation that evaporates before reaching the ground.
Topic: 
climatology and meteorology

viscosity

a measure of a fluid’s resistance to flow; can be thought of as a measure of fluid friction.
Topic: 
climatology and meteorology

visibility

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

Topic: 
climatology and meteorology

visualization

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).
Topic: 
frozen ground or permafrost

volumetric heat capacity

the amount of heat required to raise the temperature of a unit volume of a substance by one degree.
Topic: 
frozen ground or permafrost

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.
Topic: 
frozen ground or permafrost

warm front

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

Topic: 
climatology and meteorology

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.
Topic: 
climatology and meteorology

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.

Topic: 
climatology and meteorology

water vapor

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

Topic: 
climatology and meteorology

waterbody encircling a palsa

a water-filled depression surrounding a palsa.
Topic: 
frozen ground or permafrost

watermelon snow

snow with red algae growing on it.
Topic: 
snow

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.
Topic: 
glaciers

weather

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.

Topic: 
climatology and meteorology

weathered ice

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

weathering

the processes of ablation and accumulation which gradually eliminate irregularities in an ice surface.
Topic: 
glaciers
icebergs and ice shelves

wedge ice

ice occurring in an ice wedge.
Topic: 
frozen ground or permafrost

well-bonded permafrost

ice-bearing permafrost in which all the soil particles are held together by ice.
Topic: 
frozen ground or permafrost

westerlies

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

whiteout

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.
Topic: 
snow

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.

Topic: 
climatology and meteorology

World Meteorological Organization Program

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

Topic: 
climatology and meteorology

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