National Snow and Ice Data Center

closed talik

a layer or body of unfrozen ground occupying a depression in the permafrost table below a lake or river.

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closed-system freezing

freezing that occurs under conditions that preclude the gain or loss of any water by the system.

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closed-system pingo

a pingo formed by doming of frozen ground due to freezing of injected water supplied by expulsion of pore water during permafrost aggradation in the closed talik under a former water body.

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cloud

a hydrometeor consisting of a visible aggregate of minute particles of liquid water or ice, or both, suspended in the free air and usually not touching the earth's surface; it may also include larger particles of liquid water or ice (precipitation particles) and non-aqueous liquid or solid particles such as those present in fumes, smoke and dust (aerosols); cloudiness is the same as cloud cover; but usually it is used in a very general sense.

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cloud amount

that portion of the sky cover which is attributed to clouds; the unit of measurement is the okta or tenths (meaning one-eighth or one-tenth) of the sky dome as seen by the observer.

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coefficient of compressibility

decrease in volume per unit volume of a substance resulting from a unit increase in pressure, under isothermic conditions.

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cold front

any non-occluded front that moves in such a way so that colder air replaces warmer air; the leading edge of a relatively cold air mass.

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cold glacier

glacier in which most of the ice is below the pressure melting point; nonetheless, the glacier's surface may be susceptible to melt due to incoming solar radiation, and the ice at the rock/ice interface may be warmed as a result of the natural (geothermal) heat from the earth's surface.

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cold low

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

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cold pole

the location that has the lowest annual mean temperature in its hemisphere.

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collapse scar

that portion of a peatland where the whole or part of a palsa or peat plateau has thawed and collapsed to the level of the surrounding peatland.

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composite wedge

a wedge showing evidence of both primary and secondary filling.

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compression flow

flow that occurs when glacier motion is decelerating down-slope.

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condensation

the physical process by which a vapor becomes a liquid or solid; the opposite of evaporation; in meteorological usage, this term is applied only to transformation from vapor to liquid; any process in which a solid forms directly from its vapor is termed sublimation, as is the reverse process.

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conduction

the transport of energy entirely resulting from the random motions of individual molecules, and not from any concerted group movement; occurs in response to temperature gradients; contrasts with convection, in which energy is transported by molecules moving together in coherent groups.

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congelation ice

an advanced form of new ice that forms as a stable sheet with a smooth bottom surface.

A photograph in natural light of the vertically oriented pores in congelation ice. (Photo courtesy of Ted Maksym, United States Naval Academy.)

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conglomeric cryogenic fabric

a distinct soil micromorphology, resulting from the effects of freezing and thawing processes, in which coarser soil particles form compound arrangements.

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consolidated pack ice

pack ice in which the floes are frozen together; ice cover 10/10ths.

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construction methods in permafrost

special design and construction procedures required when engineering works are undertaken in permafrost areas.

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constructive metamorphism

snow metamorphism that adds molecules to sharpen the comers and edges of an ice crystal.

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continuous permafrost

geographic area in which permafrost occurs everywhere beneath the exposed land surface with the exception of widely scattered sites, such as newly deposited unconsolidated sediments that have just been exposed to the freezing climate; mean annual soil surface temperatures are typically below -5 degrees Celsius (23 degrees Fahrenheit).

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continuous permafrost zone

the major subdivision of a permafrost region in which permafrost occurs everywhere beneath the exposed land surface with the exception of widely scattered sites.

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convection

the transport of energy resulting from the concerted movement of molecules in coherent groups; contrasts with conduction in which energy is transported by the random motions of molecules; atmospheric convection is nearly always turbulent and results in the vertical transport and mixing of atmospheric properties.

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convection cloud

cumuliform cloud which forms in the atmosphere as a result of convection; such clouds are also called clouds of vertical development, a cloud that has its base in the low height range but extends upward into the middle or high altitudes.

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coriolis force

apparent force, due to the rotation of the earth, which acts normal to, and to the right of the velocity of a moving particle in the northern hemisphere, the movement of the particle being considered relative to that of the earth.

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cornice

an overhanging accumulation of ice and wind-blown snow, characteristically found on the edge of a ridge or cliff face.

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snow

crack

any fracture or rift in floating ice not sufficiently wide to be described as a lead.

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creep

a way that snow or ice can move by deforming its internal structure.

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snow

creep of frozen ground

the slow deformation (or time-dependent shear strain) that results from long-term application of a stress too small to produce failure in the frozen material.

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creep strength

the failure strength of a material at a given strain rate or after a given period under deviatoric stress.

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crevasse

open fissure in the glacier surface.

Explorers examine a crevasse on Lyman Glacier in 1916. (Photo courtesy of the United States Forest Service. Archived at the World Data Center for Glaciology, Boulder, CO.)

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crevasse hoar

a kind of hoarfrost; ice crystals that develop by sublimation in glacial crevasses and in other cavities with cooled space and calm, still conditions under which water vapor can accumulate; physical origin is similar to depth hoar.

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crust

a hard snow surface lying upon a softer layer; crust may be formed by sun, rain or wind, and is described as breakable crust or unbreakable crust, depending upon whether it wil break under the weight of a turning skier.

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snow

crust-like cryostructure

the cryostructure of a frozen deposit of angular blocks that are coated with ice, whereas large spaces between the blocks are not filled with ice.

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cryoconite

A deposit of dust and soot, often bound by microbial mats, that is formed on melting glaciers and ice sheets. The deposits are often found in pothole-like pockets on the ice surface.

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