climatology and meteorology

pressure melting

melting that occurs in ice at temperatures colder than normal melting temperature because of added pressure.

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.

present weather

weather at a station at the time of observation.

precision

the degree of agreement between independent measurements of a single quantity obtained by applying a specific measurement procedure several times under prescribed conditions.

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.

polyarnik

Russian word for a person working for a long time at one of the polar observing stations.

polar day

in 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, 34 minutes N or S) to 186 days at the north and south poles.

polar night

in 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, 34 minutes N or S) to 179 days at the North and South Poles.

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.

polar vortex

large-scale cyclonic circulation in the middle and upper troposphere centered generally in the polar regions; it is often called circumpolar vortex.

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