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solifluction sheet

a broad deposit of nonsorted, water-saturated, locally derived materials that is moving or has moved downslope.

solifluction terrace

a low step, or bench, with a straight or lobate front, the latter reflecting local differences in the rate of solifluction movement.


the point in time when the vertical rays of the sun are striking either the Tropic of Cancer (23 degrees, 30 minutes N, the summer solstice in the northern hemisphere) or the Tropic of Capricorn (23 degrees, 30 minutes S, the winter solstice in the northern hemisphere); represents the longest or shortest day of the year; in the northern hemisphere, the summer solstice falls on or about 21 June, and the winter solstice on or about 22 December.

sorted circle

a patterned ground form that is equidimensional in several directions, with a dominantly circular outline, and a sorted appearance commonly due to a border of stones surrounding a central area of finer material.

sorted net

a type of patterned ground with cells that are equidimensional in several directions, neither dominantly circular nor polygonal, with a sorted appearance commonly due to borders of stones surrounding central areas of finer material.

sorted polygon

a patterned ground form that is equidimensional in several directions, with a dominantly polygonal outline, and a sorted appearance commonly due to a border of stones surrounding a central area of finer material.

sorted step

a patterned ground feature with a step-like form and a downslope border of stones embanking an area of relatively fine-grained bare ground upslope.

sorted stripe

patterned ground with a striped and sorted appearance, due to parallel strips of stones and intervening strips of finer material, oriented down the steepest available slope.

south pole

90° S latitude; one of the two points where the Earth's axis of rotation meets the Earth's surface (the other being the north pole, diametrically opposite).

specific heat capacity

the amount of heat required to raise the temperature of a unit mass of a substance by one degree.

specific humidity

the mass of water vapor per unit mass of air, including the water vapor (usually expressed as grams of water vapor per kilogram of air).

splay crevasse

a crevasse pattern that forms where ice slowly spreads out sideways; commonly found near a glacier terminus.

sporadic discontinuous permafrost

(1) (North American usage) permafrost underlying 10 - 50% of the exposed land surface (2) (Russian usage) permafrost underlying 5 - 30% of the exposed land surface.

spring equinox

either of the two points of intersection of the sun's apparent annual path and the plane of the earth's equator; in the northern hemisphere, the spring (vernal) equinox falls on or about 21 March, and the autumnal equinox on or about 22 September.

stable air mass

air mass having static stability in its lower layers; it is free from convection, has a low degree of turbulence and may have stratiform clouds or fog, or no clouds.


thick ridges that become grounded during the winter and become part of the fast ice zone; while the rest of the fast ice melts during the summer, a stamukhi remains throughout the summer attached to the ocean bottom.

standard deviation

Statistical measurement of the variation in a distribution: In science, standard deviation serves as measure of the spread of the data, or how likely a data point will fall close to the mean.

static cryosol

a mineral soil showing little or no evidence of cryoturbation, with permafrost within 1 meter (3.3 feet) below the surface.

station pressure

atmospheric pressure observed at a station.

steam fog

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 sea smoke.

steering flow

in meteorology, a basic fluid flow which exerts a strong influence upon the direction of movement of disturbances embedded in it; in the atmosphere, it is usually an air flow in the middle or upper troposphere which govern directions of the disturbances at low levels.

stone earth circle

a type of nonsorted circle developed in gravelly materials.

stone garland

the downslope border of stones along a sorted step, embanking an area of relatively fine-grained bare ground upslope.

stone-banked (solifluction) lobe

a solifluction lobe with a stony front.

stone-banked (solifluction) terrace

a solifluction terrace with a stony front.

strand crack

a fissure at the junction between an inland ice sheet, ice piedmont or ice rise and an ice shelf, the latter being subject to the rise and fall of the tide.


a principal low-level cloud type (cloud genus), predominantly stratiform, in the form of relatively low gray and/or whitish layer, sheet or patch; its elements are often arranged in bands or rolls that lie across the wind; light rain, snow, or sleet may fall from stratocumulus.


the boundary layer between the stratosphere and the mesosphere at about 50 to 55 kilometers (31 to 34 miles).


a layer of the Earth’s atmosphere, between the troposphere and mesosphere, that is stratified in temperature such that cooler layers are closer to the Earth’s surface, and warmer layers are higher up (opposite the pattern of the troposphere near the Earth’s surface); situated between about 10 to 50 kilometers (6 to 31 miles) in altitude above the surface of the moderate latitudes; at the poles, it starts at about 8 km in altitude; composition is basically the same as that of the lower atmosphere, with the addition of ozone.


a principal low-level cloud type (cloud genus) in the form of a low-altitude, light to dark gray cloud layer with a rather uniform base; generally diffuse and dull; this cloud formation has little structure and looks like fog, except that it is above the ground, stratus does not usually produce precipitation, but when it does occur, it is in the form of minute particles, such as drizzle, ice crystals, or fine snow grains.

string fen

a peatland with roughly parallel narrow ridges of peat dominated by fenland vegetation interspersed with slight depressions, many of which contain shallow pools.


a long narrow area of pack ice, about 1 kilometer (0.6 mile) or less in width, usually composed of small fragments detatched from the main mass of ice, and run together under the influence of wind or current.

subglacial permafrost

permafrost beneath a glacier.

subglacial talik

a layer or body of unfrozen ground beneath a glacier in an area with permafrost.


the transition of a substance from the solid phase directly to the vapor phase, or vice versa, without passing through an intermediate liquid phase.

sublimation ice

ice formed by reverse sublimation of water vapour on cold surfaces.