National Snow and Ice Data Center

radiation

(1) emission or transfer of energy in the form of electromagnetic waves (2) the process by which electromagnetic radiation is propagated through free space by virtue of joint undulatory variations in the electric and magnetic fields in space; this concept is to be distinguished from conduction and convection.

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radiosonde

instrument intended to be carried by a balloon up through the atmosphere, equipped with sensors to measure one or several meteorological variables (pressure, temperature, humidity, etc.), and provided with a radio transmitter for sending this information to the observing station.

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radius-dependent metamorphism

snow metamorphism that occurs when there are large differences in convex and concave portions of a crystal.

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snow

rafted ice

deformed sea ice in which one piece has overridden another; also called telescoped ice.

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rafting

a process by which currents or winds push around thin ice so they slide over each other; also called finger rafting.

Nilas showing finger rafting. (Photo courtesy of the Antarctic Sea-Ice Processes and Climate program (ASPeCt).)

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ram

a horizontal underwater projection of ice from an ice front, ice wall, iceberg or floe.

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randkluft

a fissure that separates a moving glacier from its headwall rock; like a bergschrund.

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rawinsonde

radiosonde which is tracked by radar or radio-theodolite to measure the wind aloft.

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reconstituted glacier

a glacier that is reconstructed or reconstituted out of other glacier material; usually formed by seracs falling from a hanging glacier then re-adhering; also called reconstructed glacier, regenerated glacier, or glacier remainie.

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reconstructed glacier

a glacier that is reconstructed or reconstituted out of other glacier material; usually formed by seracs falling from a hanging glacier then re-adhering; also called reconstituted glacier, regenerated glacier, or glacier remainie.

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recurring 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.

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red algae

algae common on temperate glaciers and perennial snow; its red color sometimes prompts people to call it watermelon snow.

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snow

reformatting

Provides the user the ability to convert the data from its native format to a different format.

regelation

motion of an object through ice by melting and freezing that is caused by pressure differences; this process allows a glacier to slide past small obstacles on its bed.

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regenerated glacier

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relative error

The ratio of the absolute error in a measurement to the size of the measurement.

relative humidity

the (dimensionless) ratio of the actual vapor pressure of the air to the saturation vapor pressure; usually expressed as a percent, and can be computed from psychrometric data.

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relative permittivity

the relative permitivity of a soil is the ratio of the permitivity of the soil to the permitivity of a vacuum.

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relict active layer

a layer of ground, now perennially frozen, lying immediately below the modern active layer; its thickness indicates the greater annual depth of thaw that occurred during a previous period.

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relict ice

ice formed in, and remaining from, the geologically recent past.

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relict permafrost

permafrost existing in areas where permafrost can not form under present climatic conditions; reflects past climatic conditions that were colder.

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reprojection

Provides the user the ability to convert the data from its native reference projection to a different reference projection.

residual stress

the effective stress generated in a thawing soil if no volume change is permitted during thaw.

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residual thaw layer

a layer of thawed ground between the seasonally frozen ground and the permafrost table.

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reticulate cryostructure

the cryostructure in which horizontal and vertical ice veins form a three-dimensional, rectangular or square lattice.

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reticulate ice

a network of horizontal and vertical ice veins forming a three-dimensional, often rectangular or square lattice.

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reticulate-blocky cryostructure

the cryostructure in which horizontal and vertical ice veins form a three-dimensional, irregular rectangular lattice.

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retreat

when a mountain glacier's terminus doesn't extend as far downvalley as it previously did; occurs when ablation surpasses accumulation.

Muir Glacier, Glacier Bay National Park and Reserve's White Thunder Ridge as seen on August 13, 1941 (left) and August 31, 2004 (right). (2004 USGS photo courtesy of B. Molnia; 1941 photo courtesy of W. Field. Archived at the Long-Term Change Photograph Pairs Special Collection in the Glacier Photograph Database.)

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retreating glacier

a glacier whose terminus is increasingly retreating upvalley compared to its previous position due to a higher level of ablation compared to accumulation.

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retrogressive thaw slump

a slope failure resulting from thawing of ice-rich permafrost.

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ridge

in meteorology, an elongated area of relatively high atmospheric pressure, almost always associated with and most clearly identified as an area of maximum anticyclonic curvature of wind flow.

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ridge ice

piled ice formed by ridging.

Ridged sea ice. (Photo courtesy of Don Perovich, U.S. Army Cold Regions Research and Engineering Laboratory.)

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ridging

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.

Ridged sea ice. (Photo courtesy of Don Perovich, U.S. Army Cold Regions Research and Engineering Laboratory.)

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rime

a white or milky and opaque granular deposit of ice formed by the rapid freezing of super-cooled water drops as they impinge upon an exposed object; it is denser and harder than hoarfrost, but lighter, softer, and less transparent than glaze.

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