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sea surface temperature

temperature of the water film at the sea surface.

sea-level pressure

the atmospheric pressure at mean sea level, either directly measured or, most commonly, empirically determined from the observed station pressure.


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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.

seasonal frost

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

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.

seasonal snow

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

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.

seasonally frozen ground

ground that freezes and thaws annually.

seasonally frozen layer (SFL)

the active layer in areas without permafrost.

seasonally thawed ground

ground that thaws and refreezes annually.

seasonally thawed layer (STL)

the active layer in permafrost areas.

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.

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.

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.

segregated ice

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

segregation potential

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

semipermanent anticyclone

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

semipermanent depression

slowly moving or motionless cyclone.

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.

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.


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

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.


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

shore lead

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

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).

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.


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).)

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.


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.

single-phase thermosyphon

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


the bonding together of ice crystals.


(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.

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.


a mixture of snow and grease ice.

slush zone

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