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summer minimum extent

the permanent ice zone that remains in summer after all melting has occurred.

sun cups

ablation hollows that develop during intense sunshine.


dark spot on the sun, with cooler-than-average temperatures and strong magnetic activity


the condition when a liquid remains in the liquid state even through its temperature is below its freezing point.


cooling of a liquid to a temperature below its freezing point, without causing solidification.


the condition which occurs in the atmosphere when the relative humidity is greater than 100%.

suprapermafrost water

water occurring in unfrozen ground above perennially frozen ground.

surface cryogenic fabric

a distinct soil micromorphology, resulting from the effects of freezing and thawing processes, in which coarser soil particles have vertical or near-vertical orientation.

surface freezing index

the cumulative number of degree-days below 0 degrees Celsius for the surface temperature (of the ground, pavement, etc.) during a given time period.

surface hoar

the deposition (sublimation) of ice crystals on a surface which occurs when the temperature of the surface is colder than the air above and colder than the frost point of that air.


surface observation

a meteorological observation made on the earth's surface, in contrast with an upper-air observation.

surface temperature

the ambient temperature indicated by a thermometer exposed to the air but sheltered from direct solar radiation, or placed in an instrument shelter 1.5 - 2.0 meters (5.0 - 6.6 feet) above ground; also called air temperature.

surface wind

wind blowing near the earth's surface; it is measured, by convention, at a height of 10 meters (33 feet) above ground in an area where the distance between the anemometer and any obstruction is at least 10 times the height of the obstruction.

surging glacier

a glacier that experiences a dramatic increase in flow rate, 10 to 100 times faster than its normal rate; usually surge events last less than one year and occur periodically, between 15 and 100 years.
In 1941, Hole-in-the-Wall Glacier surged, also knocking over trees during its advance. (Photo courtesy of the World Data Center for Glaciology, Boulder, CO. Photo probably taken by W.O. Field.)


a substance dispersed throughout another substance; also called suspended phase.

syngenetic ice

ground ice developed during the formation of syngenetic permafrost.

syngenetic ice wedge

an ice wedge developed during the formation of syngenetic permafrost.

syngenetic permafrost

permafrost that formed through a rise of the permafrost table during the deposition of additional sediment or other earth material on the ground surface.

synoptic analysis

the study of the synoptic observation data plotted on synoptic charts aimed at analysis of the atmospheric disturbances (for example, fronts, cyclones, and anticyclones).

synoptic chart

a weather chart reflecting the state of the atmosphere over a large area at a given moment.

synoptic code

a code approved by the World Meteorological Organization, by which meteorological elements observed at the earth's surface at synoptic times are encoded in groups of five figures and transmitted internationally through the GTS (Global Telecommunications System).

synoptic hour

hour (UTC - Coordinated Universal Time) determined by international agreement at which meteorological observations are made simultaneously throughout the world; the primary synoptic hours are every six hours, commencing at 00:00 UTC.

synoptic meteorology

the study and analysis of synoptic weather information (synoptic charts, synoptic weather observations); thus, it is a study of macro-scale atmospheric processes, as well as weather prediction based on results of synoptic studies.

synoptic weather observation

an observation made at periodic times (usually at 3-hour and 6-hour intervals specified by the World Meteorological Organization) of sky cover, state of the sky, cloud height, atmospheric pressure at sea level, temperature, dew point, wind speed and direction, amount of precipitation, hydrometeors and lithometeors, and special phenomena that prevail at the time of the observation or observed since the previous specified observation.


the scale of the high- and low-pressure systems of the lower atmosphere; dimensions typically range from 1000 to 2500 kilometers (620 to 1550 miles; synoptic-scale circulation).

tabular berg

a flat-topped iceberg that shows horizontal banding; typically form by breaking from an ice shelf.


the open northern part of the boreal forest; consists of open woodland of coniferous trees growing in a rich floor of lichen (mainly reindeer moss or caribou moss), and is generally cold and swampy; lies immediately south of the tundra; in spring, it is often flooded by water from northward flowing rivers, the lower reaches of which are still frozen.


a layer or body of unfrozen ground occurring in a permafrost area due to a local anomaly in thermal, hydrological, hydrogeological, or hydrochemical conditions.


a small mountain lake or pool.

telescoped ice

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


a physical quantity characterizing the mean random motion of molecules in a physical body; in other words, it is a measure of the degree of hotness or coldness of a substance.

temperature profile

the graphic or analytical expression of the variation in ground temperature with depth.

temperature-gradient metamorphism

snow metamorphism that occurs when there are strong differences in temperature between the bottom and top of a snow layer.


the lowest end of a glacier, also called the glacier toe or glacier snout.
Glacier at the head of Canon Fiord, Ellesmere Island, Canada

terrestrial radiation

longwave radiation emitted by the earth, including its atmosphere.

thaw bulb

a zone of thawed ground below or surrounding a man-made structure placed on or in permafrost and maintained at temperatures above 0 degrees Celsius.