National Snow and Ice Data Center

pancake ice

pieces of new ice approximately circular, up to 10 centimeters (4 inches) thick and 0.03 to 3 meters (0.1 to 9.8 feet) in diameter, with raised edges that form from rubbing against each other; formed from the freezing together of grease ice, slush or shuga, or the reaking up of ice rind or nilas.

(Photo courtesy of the National Oceanic and Atmospheric Administration/Department of Commerce.)

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sea ice

parameter

(1) a term used loosely by many meteorologists for almost any meteorological quantity or element (2) an arbitrary constant or variable appearing in a mathematical expression; changing it can give various outcomes for the phenomena represented.

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partial pressure

in a mixture of gases, each gas has a partial pressure, which is the pressure the gas would have if it occupied that volume alone.

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partially-bonded permafrost

ice-bearing permafrost in which some of the soil particles are not held together by ice.

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passive construction methods in permafrost

special design and construction methods used for engineering works in permafrost areas where preservation of the frozen condition is feasible.

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passive single-phase thermal pile

a foundation pile provided with a single-phase natural convection cooling system to remove heat from the ground.

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passive two-phase thermal pile

a foundation pile provided with a two-phase natural convection cooling system to remove heat from the ground.

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past weather

predominant characteristic of the weather which had existed at an observing station during a given period of time (during the preceding hour or six hours), specified in the international synop code.

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patch

a collection of pack ice, less than 10 kilometers (6.2 miles) across, whose limits can be seen from the masthead.

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sea ice

patterned ground

a general term for any ground surface exhibiting a discernibly ordered, more or less symmetrical, morphological pattern of ground and, where present, vegetation.

A photograph taken from the air reveals patterned ground surrounding thaw lakes in Alaskas Arctic National Wildlife Refuge. Credit: U.S. Fish and Wildlife Service

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peat

a deposit consisting of decayed or partially decayed humified plant remains.

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peat hummock

a hummock consisting of peat.

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peat plateau

a generally flat-topped expanse of peat, elevated above the general surface of a peatland, and containing segregated ice that may or may not extend downward into the underlying mineral soil.

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peatland

peat-covered terrain.

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penitents

the extreme relief of ablation hollows found most often at high altitudes in the tropics; the resulting spikes of snow resemble repentant souls.

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snow

pereletok

a layer of frozen ground which forms as part of the seasonally frozen ground (in areas free of permafrost or with a lowered permafrost table); remains frozen throughout one or several summers, and then thaws.

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perennial snow

snow that persists on the ground year after year.

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snow

periglacial

the conditions, processes and landforms associated with cold, nonglacial environments.

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periglacial phenomena

landforms and soil characteristics produced by periglacial processes.

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periglacial processes

processes associated with frost action in cold, nonglacial environments.

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permacrete

an artificial mixture of frozen soil materials cemented by pore ice, which forms a concrete-like construction material used in cold regions.

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permafrost

layer of soil or rock, at some depth beneath the surface, in which the temperature has been continuously below 0°C for at least several years; it exists where summer heating fails to reach the base of the layer of frozen ground.

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permafrost aggradation

a naturally or artificially caused increase in the thickness and/or areal extent of permafrost.

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permafrost base

the lower boundary surface of permafrost, above which temperatures are perennially below 0 degrees Celsius (cryotic) and below which temperatures are perennially above 0 degrees Celsius (noncryotic).

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permafrost boundary

(1) the geographical boundary between the continuous and discontinuous permafrost zones (2) the margin of a discrete body of permafrost.

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permafrost degradation

a naturally or artificially caused decrease in the thickness and/or areal extent of permafrost.

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permafrost extent

the total geographic area containing some amount of permafrost; typically reported in square kilometers.

permafrost limit

outermost (latitudinal) or lowest (altitudinal) limit of the occurrence of permafrost.

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permafrost region

a region in which the temperature of some or all of the ground below the seasonally freezing and thawing layer remains continuously at or below 0 degrees Celsius for at least two consecutive years.

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permafrost table

the upper boundary surface of permafrost.

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permafrost thickness

the vertical distance between the permafrost table and the permafrost base.

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permafrost zone

a major subdivision of a permafrost region.

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permanent ice zone

a region that is covered with sea ice year-round; most of the sea ice in the permanent ice zone is multiyear ice, but younger ice and open water may still be present; the permanent ice zone is what remains in summer after all melting has occurred (often called the summer minimum extent).

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sea ice

pH

power of hydrogen; a measure of the activity of hydrogen ions in solution, and therefore, its acidity or alkalinity.

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