National Snow and Ice Data Center

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seasonal freezing index

the cumulative number of degree-days below 0 degrees Celsius, calculated as the arithmetic sum of all the negative and positive mean daily air temperatures (degrees Celsius) for a specific station during the time period between the highest point in the fall and the lowest point the next spring on the cumulative degree-day time curve.

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seasonal frost

the occurrence of ground temperatures below 0 degrees Celsius for only part of the year; see also active layer.

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seasonal ice zone

an area of ocean that extends from the permanent ice zone to the boundary where winter sea ice extent is at a maximum; here, sea ice is present only part of the year; this zone primarily consists of first-year ice.

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seasonal snow

(1) snow that accumulates during one season (2) snow that lasts for only one season.

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snow

seasonal thawing index

the cumulative number of degree-days above 0 degrees Celsius, calculated as the arithmetic sum of all the positive and negative mean daily air temperatures (degrees Celsius) for a specific station during the time period between the lowest point in the spring and the highest point the next fall on the cumulative degree-day time curve.

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seasonally frozen ground

ground that freezes and thaws annually.

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seasonally frozen layer (SFL)

the active layer in areas without permafrost.

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seasonally thawed ground

ground that thaws and refreezes annually.

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seasonally thawed layer (STL)

the active layer in permafrost areas.

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seasonally-active permafrost

the uppermost layer of the permafrost which undergoes seasonal phase changes due to the lowered thawing temperature and freezing-point depression of its pore water.

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second-year ice

sea ice which has not melted in the first summer of its existence; by the end of the second winter, it attains a thickness of 2 meters (6.6 feet) or more; it stands higher out of the water than first-year ice; summer melting has somewhat smoothed and rounded the hummocks, which accentuation of minor relief by differential melting may have caused others to develop; bare patches and puddles are usually greenish-blue.

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sedimentary ogives

alternating bands of light and dark at the firn limit of a glacier; the light bands are usually young and lightest at the highest level up-glacier, becoming increasingly older and darker as they progress down-glacier.

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segregated ice

ice in discrete layers or ice lenses, formed by ice segregation.

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segregation potential

the ratio of the rate of moisture migration to the temperature gradient in a frozen soil near the 0 degrees Celsius isotherm.

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semipermanent anticyclone

high pressure area largely predominate during a major portion of the year where an anticyclone appears on the mean monthly pressure charts.

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semipermanent depression

slowly moving or motionless cyclone.

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sensible heat

same as enthalpy; the heat absorbed or transmitted by a substance during a change of temperature which is not accompanied by a change of state; used in meteorology in contrast to latent heat.

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sensible heat polynya

a polynya that forms from the upwelling of warm (above-freezing) ocean water from lower depths; these can form in mid-ocean areas, far from coasts or other barriers.

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serac

an isolated block of ice that is formed where the glacier surface is fractured.

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shear strength

in geology, describes the compressive strength (ability to withstand pushing forces) of soils; results from two internal mechanisms: cohesion between soil particles, and friction caused by contact between particles; variable among different soils.

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shield

a screen to shield a rain-gauge from the influence of the wind, or to shield a thermometer against insolation.

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shore lead

a stretch of navigable water between pack ice and the shore.

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short-term strength

the failure strength of a material under a short-term loading (e.g. up to about 10 minutes in a uniaxial compression test).

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shortwave radiation

in meteorology, a term used loosely to distinguish radiation in the visible and near-visible portions of the electromagnetic spectrum (roughly 0.4 to 4.0 microns in wavelength) from longwave (terrestrial) radiation.

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shuga

a form of new ice, composed of spongy, white lumps a few cm across, that tend to form in rough seas; they resemble slushy snow balls.

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

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Siberian high

an area of high pressure which forms over Siberia in winter, and which is particularly apparent on mean charts of sea-level pressure.

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sikussak

very old, thick sea ice that forms in fjords; it often resembles glacial ice, because snow can pile up on the ice over many years.

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single-phase thermosyphon

a passive heat transfer device, filled with either a liquid or a gas, installed to remove heat from the ground.

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sintering

the bonding together of ice crystals.

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sleet

(1) (United States) frozen raindrops that bind on impact with the ground (2) (elsewhere) a mix of rain and snow, a mix of rain and hail, or melting snow.

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slope failure

mass movement of earth material down a slope; includes landslides, mudslides, debris flows, avalanches, etc; speed of movement can be sudden and catastrophic or slow.

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slush

a mixture of snow and grease ice.

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snow

slush zone

common near the snow line on a relatively flat portion of a glacier where melting snow forms slush.

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