Cryosphere glossary
polygonal peat plateau
a peat plateau with ice-wedge polygons.
polynya
irregularly shaped areas of persistent open water that are sustained by winds or ocean heat; they often occur near coasts, fast ice, or ice shelves.
Image
Satellite view of polynyas (dark areas) near Oates Coast, Antarctica (solid white area at bottom of photo).
NASA
poorly-bonded permafrost
ice-bearing permafrost in which few of the soil particles are held together by ice.
pore ice
ice occurring in the pores of soils and rocks.
pore water
water occurring in the pores of soils and rocks.
post-glacial rebound
Post-glacial rebound (sometimes called continental rebound, isostatic rebound or isostatic adjustment) is the rise of land masses that were depressed by the huge weight of ice sheets during the last ice age.
pothole
a 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 snow
a thin, dry snow surface which is composed of loose, fresh ice crystals.
prairie
a 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.
precision
the degree of agreement between independent measurements of a single quantity obtained by applying a specific measurement procedure several times under prescribed conditions.
present weather
weather at a station at the time of observation.
pressure
a 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 ice
a 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 melting
melting that occurs in ice at temperatures colder than normal melting temperature because of added pressure.
pressure ridge
process 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 tendency
the character and amount of atmospheric pressure change for a three-hour or other specified period ending at the time of observation.
pressure-melting
lowering the melting point of ice by applying pressure.
prime meridian
the 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.
pseudomorph
in 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.