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ice that is not attached to the shoreline and drifts in response to winds, currents, and other forces; some prefer the generic term drift ice, and reserve pack ice to mean drift ice that is closely packed.
palsaa peaty permafrost mound possessing a core of alternating layers of segregated ice and peat or mineral soil material.
palsa boga poorly-drained lowland underlain by organic-rich sediments, which contains perennially frozen peat bodies (peat plateaux) and, occasionally, palsas.
pancake icepieces 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.

(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.
partial pressurein a mixture of gases, each gas has a partial pressure, which is the pressure the gas would have if it occupied that volume alone.
partially-bonded permafrostice-bearing permafrost in which some of the soil particles are not held together by ice.
passive construction methods in permafrostspecial design and construction methods used for engineering works in permafrost areas where preservation of the frozen condition is feasible.
passive single-phase thermal pilea foundation pile provided with a single-phase natural convection cooling system to remove heat from the ground.
passive two-phase thermal pilea foundation pile provided with a two-phase natural convection cooling system to remove heat from the ground.
past weatherpredominant 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.
patcha collection of pack ice, less than 10 kilometers (6.2 miles) across, whose limits can be seen from the masthead.
patterned grounda general term for any ground surface exhibiting a discernibly ordered, more or less symmetrical, morphological pattern of ground and, where present, vegetation.

a deposit consisting of decayed or partially decayed humified plant remains.
peat hummocka hummock consisting of peat.
peat plateaua 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.
peatlandpeat-covered terrain.
penitentsthe extreme relief of ablation hollows found most often at high altitudes in the tropics; the resulting spikes of snow resemble repentant souls.
pereletoka 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.
perennial snowsnow that persists on the ground year after year.
periglacialthe conditions, processes and landforms associated with cold, nonglacial environments.
periglacial phenomenalandforms and soil characteristics produced by periglacial processes.
periglacial processesprocesses associated with frost action in cold, nonglacial environments.
permacretean artificial mixture of frozen soil materials cemented by pore ice, which forms a concrete-like construction material used in cold regions.
permafrostlayer 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.
permafrost aggradationa naturally or artificially caused increase in the thickness and/or areal extent of permafrost.
permafrost basethe 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).
permafrost boundary(1) the geographical boundary between the continuous and discontinuous permafrost zones (2) the margin of a discrete body of permafrost.
permafrost degradationa naturally or artificially caused decrease in the thickness and/or areal extent of permafrost.
permafrost extentthe total geographic area containing some amount of permafrost; typically reported in square kilometers.
permafrost limitoutermost (latitudinal) or lowest (altitudinal) limit of the occurrence of permafrost.
permafrost regiona 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.
permafrost tablethe upper boundary surface of permafrost.
permafrost thicknessthe vertical distance between the permafrost table and the permafrost base.
permafrost zonea major subdivision of a permafrost region.
permanent ice zonea 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).
pHpower of hydrogen; a measure of the activity of hydrogen ions in solution, and therefore, its acidity or alkalinity.
piedmont glacierlarge ice lobe spread out over surrounding terrain, associated with the terminus of a large mountain valley glacier.

an eskimo term for a perennial frost mound consisting of a core of massive ice with soil and vegetation cover; the size can range from a few meters to tens of meters, in both diameter and height; can be found in continuous and discontinuous permafrost zones.
pingo icemassive ice forming the core of a pingo.
pingo remnanta collapsed pingo.
pingo scara pingo remnant in a contemporary non-permafrost environment.
planetary permafrostpermafrost occurring on other planetary bodies (planets, moons, asteroids).
plastic frozen groundfine-grained soil in which only a portion of the pore water has turned into ice.
Pleistocenepart of the geologic timescale, corresponding to the time period from 1.81 million to 11,550 years before the present.
Poisson's ratiothe absolute value of the ratio between linear strain changes, perpendicular to and in the direction of a given uniaxial stress change.
polar dayin polar regions, the portion of the year when the sun is continuously in the sky; its length changes from twenty hours at the arctic/antarctic circle (latitude 66 degrees, 33 minutes N or S) to 186 days at the north and south poles.
polar explorera person working for a long time at one of the polar observing stations; Russian word is polyarnik.
polar glaciera glacier entirely below freezing, except possibly for a thin layer of melt near the surface during summer or near the bed; polar glaciers are found only in polar regions of the globe or at high altitudes.
polar ice capa high-latitude region covered in ice; not a true ice cap, which are less than 50,000 square kilometers (12.4 million acres) and are always over land; more like an ice sheet; also called polar ice sheet.
polar lowsmall, shallow depression which forms mainly in winter over some high-latitude seas within a polar or arctic air mass; its motion is approximately the same as the air stream in which it is embedded.
polar nightin polar regions, the portion of the year when the sun does not rise above the horizon; its length changes from twenty hours at the arctic/antarctic circle (latitude 66 degrees, 33 minutes N or S) to 179 days at the North and South Poles.
polar regionregions around the North and South Poles, north of the Arctic, or south of the Antarctic Circles, respectively; characterized by polar climate, very cold temperatures, heavy glaciation, and dramatic variations in daylight hours (24 hrs darkness in winter, 24 hrs daylight in summer).
polar vortexlarge-scale cyclonic circulation in the middle and upper troposphere centered generally in the polar regions; it is often called circumpolar vortex.
pole of inaccessibilityin the northern hemisphere, the point in the Arctic Ocean farthest from land; in the southern hemisphere, the point on the Antarctic continent farthest from the Southern Ocean.
polyarnikRussian word for a person working for a long time at one of the polar observing stations.
polycrystala snowflake composed of many individual ice crystals.
polygonliterally means many angled; polygons are closed, multi-sided, roughly equidimensional shapes, bounded by more or less straight sides; some of the sides may be irregular; in cryospheric science, it refers to patterned ground formations.
polygon troughthe narrow depression surrounding a high-centre polygon.
polygonal patterna pattern consisting of numerous multi-sided, roughly equidimensional figures bounded by more or less straight sides.
polygonal peat plateaua peat plateau with ice-wedge polygons.
polynyairregularly shaped areas of persistent open water that are sustained by winds or ocean heat; they often occur near coasts, fast ice, or ice shelves.

ice-bearing permafrost in which few of the soil particles are held together by ice.
pore iceice occurring in the pores of soils and rocks.
pore waterwater occurring in the pores of soils and rocks.
potholea nearly vertical channel in ice that is formed by flowing water; usually found after a relatively flat section of glacier in a region of transverse crevasses; also called a moulin.
powder snowa thin, dry snow surface which is composed of loose, fresh ice crystals.
prairiea treeless grassy plain.
precipitation(1) any of the forms of water particles, whether liquid or solid, that fall from the atmosphere and reach the ground; includes: rain, drizzle, snow, snow grains, snow pellets, diamond dust, hail, and ice pellets; see also acid precipitation (2) accumulated depth of rain, drizzle and the melted water content of frozen forms of precipitation.
precisionthe degree of agreement between independent measurements of a single quantity obtained by applying a specific measurement procedure several times under prescribed conditions.
present weatherweather at a station at the time of observation.
pressurea type of stress characterized by uniformity in all directions; in dynamics, it is that part of the stress tensor that is independent of viscosity and depends only upon the molecular motion appropriate to the local temperature and density; it is the negative of the mean of the three normal stresses, and is, therefore, a scalar quantity expressed in units of force per unit area; in meteorology, commonly used for atmospheric pressure.
pressure icea general term for floating ice which has been squeezed together and in places forced upwards; includes rafted ice, telescoped ice, hummocked ice and ridge ice.
pressure meltingmelting that occurs in ice at temperatures colder than normal melting temperature because of added pressure.
pressure ridgeprocess that occurs when wind, ocean currents, and other forces push sea ice around into piles that rise and form small mountains above the level sea ice surface; ridges are initially thin and transparent with very sharp edges from blocks of ice piling up; also see keels.
pressure tendencythe character and amount of atmospheric pressure change for a three-hour or other specified period ending at the time of observation.
pressure-meltinglowering the melting point of ice by applying pressure.
prime meridianthe meridian (line of longitude) defined to be 0 degrees and passing through the Royal Greenwich Observatory in London; also known as the International Meridian or Greenwich Meridian; the Prime Meridian and the opposite 180th meridian (at 180 degrees longitude) separate the Eastern and Western Hemispheres.
pseudomorphin geology, a mineral compound resulting from a process by which the primary mineral component is replaced by another, although the compound maintains constant appearance and dimensions.
psychrometeran instrument used for measuring the water vapor content of the atmosphere; a type of hygrometer; it consists of two thermometers, one of which (the dry bulb) is an ordinary glass thermometer, while the other (wet bulb) has its bulb covered with a jacket of clean muslin which is saturated with distilled water prior to an observation; when the bulbs are suitably ventilated, they indicate the thermodynamic wet- and dry-bulb temperatures of the atmosphere; one variety is the assman psychrometer (a special form of aspiration psychrometer for which the ventilation is provided by a suction fan).
psychrometric tablestables prepared from psychrometric data and used to obtain vapor pressure, relative humidity, and dew point from wet- and dry-bulb temperatures.
puddlean accumulation of melt water on an ice surface, mainly due to melting snow, but in later stages also to the melting of ice; the initial stage consists of patches of slush.
push morainemoraine built out ahead of an advancing glacier.
