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the part of a ridge above sea level; like a sail on a sailboat, it catches wind and moves the ice.

saline permafrost

permafrost in which part or all of the total water content is unfrozen because of freezing-point depression due to a high dissolved-solids content of the pore water.


(1) a general property of aqueous solutions caused by the alkali, alkaline earth, and metal salts of strong acids (Cl, SO4 and NO3) that are not hydrolyzed (2) in soil science, the ratio of the weight of salt in a soil sample to the total weight of the sample.

sand wedge

a wedge-shaped body of sand produced by filling of a thermal contraction crack with sand either blown in from above or washed down the walls of the crack.

sand-wedge polygon

a polygon outlined by sand wedges underlying its boundaries.


complex, fragile shapes of snow on top of sea ice that resemble sand dunes; they form parallel to the prevailing wind direction; sastrugi can also form on snow cover over land.
Sastrugi at South Pole Station, Antarctica. (Photo courtesy of Fred Walton, NOAA Corps Collection.)


the condition in which the partial pressure of any fluid constituent (water in the atmospheric air) is equal to its maximum possible partial pressure under the existing environmental conditions, such that any increase in the amount of that constituent will initiate within it a change to a more condensed state; evaporation ceases under such conditions.

saturation vapor pressure (water)

the maximum amount of water vapor necessary to keep moist air in equilibrium with a surface of pure water; this is the maximum water vapor the air can hold for any given combination of temperature and pressure.


(1) a series of marks at regular intervals for the purpose of measuring (scale of an instrument, for example, a thermometer) (2) system of units for measuring ( 3) proportion between the size of something and the map, diagram, etc. which represents it (4) order of magnitude of a phenomenon or of a meteorological parameter.

sea ice

any form of ice found at sea which has originated from the freezing of sea water.

sea ice development stage

A phrase used to classify sea ice for operational purposes using the age of the ice as a proxy for its thickness. Specific terms such as new ice, nilas, young ice, and multiyear ice are used for each stage of sea ice development.

sea ice extent


sea ice maximum extent

the day of the year when the sea ice covers the largest area of the Arctic or Antarctic.

sea ice minimum extent

the day of the year when the sea ice covers the smallest area of the Arctic or Antarctic

sea smoke

evaporation fog formed when water vapor is added to air which is much colder than the vapor's source; most commonly, when very cold air drifts across relatively warm water; also called steam fog.

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.