Glossary of Terms: S

Salinity

Concentration of dissolved salts found in a sample of water. Measured as the total amount of dissolved salts in parts per thousand. Seawater has an average salinity of about 34 parts per thousand (ppt).

Salinization

Pedogenic process that concentrates salts at or near the soil surface because evapotranspiration greatly exceeds water inputs from precipitation.

Salt

(1) The mineral sodium chloride.

(2) Compounds that are produced as the result of a metal atom replacing a hydrogen atom in an acid.

Saltation

Transport of sediment initiated by moving air or water where particles move from a resting surface to the transport medium in quick continuous repeated cycles.

Salt Marsh

Coastal wetland ecosystem that is inundated for some period of time by seawater. Plants that exist in this community have special adaptation to survive in the presence of high salinities in their immediate environment. Generally, found poleward of 30° North and South latitude.

Saltwater Intrusion

The invasion of saltwater into freshwater aquifers in coastal and inland areas. This condition can be cause when groundwater, which charges the aquifer, is withdrawn faster than it is recharged by precipitation.

Sample

A sample is a subset group of data selected from a larger population group. Most samples are drawn at random to guaranty equal representation in the data.

Sand

Mineral particle with a size between 0.06 and 2.0 millimeters in diameter. Also see clay and silt.

Sand Dune

A hill or ridge of aeolian sand deposits with a minimum height of less than one meter and a maximum height of about 50 meters. Found in hot deserts and along sandy coastlines.

Sand Sea

A large region of sand and sand dunes in a desert. Common to erg deserts.

Sand Sheet

Deposit of sometimes stratified less well sorted sand that almost resemble dunes. Common in northern Europe. Believed to form when windblown materials settle on areas of patchy snow.

Sandstone

A type of sedimentary rock that contains a large quantity of weathered quartz grains.

Sand Ripples

Another term used for wind ripples.

Sand Wedge

A form of ice wedge that contains accumulations of wind blown sand in long vertical layers. A form of periglacial ground ice.

Santa Ana Wind

A warm, dry chinook like wind that occurs in southern California. Originates from the east off an elevated desert plateau.

Saturated Adiabatic Lapse Rate (SALR)

The rate of decline in the temperature of a rising parcel of air after it has reached saturation. This rate is less than the dry adiabatic lapse rate (9.8° Celsius per 1000 meters) because of the heat energy added to the ascending air parcel from condensation and deposition processes.

Saturation

Atmospheric condition where water is changing its phase to liquid or solid. At saturation, relative humidity is 100 % unless there is a shortage of deposition nuclei or condensation nuclei. Generally, this process is caused by the cooling of the atmosphere.

Saturation Mixing Ratio

Mass of water vapor that a kilogram of dry air can hold at saturation. Measured in grams.

Savanna

A tropical or sub-tropical plant community characterized by trees and shrubs scattered among a cover of grasses, herbs and forbs. The climate of a savanna is tropical with a dry season occurring in the low sun period of the year.

Scale

A specific relative or proportional size or extent of a phenomena as measured through space and/or time.

Scarification

Extensive movements of soil, sediment, and rock material caused by humans.

Scattering (Atmospheric)

Is an atmospheric process where small particles and gas molecules diffuse part of the incoming solar radiation in random directions without any alteration to the wavelength of the electromagnetic energy. Scattering does, however, reduce the amount of incoming radiation reaching the Earth's surface. A significant proportion of scattered shortwave solar radiation is redirected back to space. The amount of scattering that takes place is dependent on two factors: wavelength of the incoming radiation and the size of the scattering particle or gas molecule. In the Earth's atmosphere, the presence of a large number of particles with a size of about 0.5 µm results in shorter wavelengths being preferentially scattered. This factor also causes our sky to look blue because this color corresponds to those wavelengths that are best diffused.

Schist

A medium to coarse grained metamorphic rock with well developed bedding planes derived from the foliated recrystrallization of platy like minerals like mica.

Science

Science is a way of acquiring knowledge. To do science, one must follow a specific universal methodology. The central theme in this methodology is the testing of hypotheses and the ability to make predictions. The overall goal of science is to better understand nature and our Universe.

Scientific Method

The approach science uses to gain knowledge. This method tries to be unbias and neutral. Involves inductive and deductive reasoning, hypothesis testing and falsification, and predictive model testing.

Sclerophyllous Vegetation

Term used to describe drought resistant vegetation common in Mediterranean climates. Some common adaptations present in this type of vegetation include: deep roots, reduced leaf area exposed to the atmosphere, and waxy thick leaves with closing stomata which resist water loss.

Scour

(1) Refers to the erosive power of water.

(2) Abrasive effects of rocks and sediments incorporated in the ice base of a glacier.

Scree

An accumulation of weathered rock fragments at the base of a steep rock slope or cliff.

Sea

(1) A body of saline water found on the Earth's continental surface.

(2) A portion of a ocean that is in close proximity to a continent.

Sea Arch

A coastal landform composed of rock that resembles an arch. These landforms are created when waves erode through a thin headland from both sides.

Sea Breeze

Local thermal circulation pattern found at the interface between land and water. In this circulation system, surface winds blow from water to land during the daytime.

Sea-Floor Spreading

The process of oceanic crust creation and sea-floor movement that occurs at the mid-oceanic ridge.

Sea-Level

The average surface elevation of the world's oceans.

Sea-Level Pressure

Average atmospheric pressure at sea-level. This value is 1013.2 millibars.

Seamount

A volcanic mountain found on an ocean basin that has an origin not related to a mid-oceanic ridge or a tectonic subduction zone.

Sea Smoke

See evaporation fog.

Seasons

Time periods generally based on the changes in the intensity and duration of sunlight as received in the middle and high latitudes. Four seasons are normally recognized: Spring; Summer; Fall; and Winter. The astronomical definition is more precise and suggests the following time periods for the four seasons: Spring - March 22 to June 21; Summer - June 22 to September 22; Fall - September 23 to December 22; and Winter - December 23 to March 21.

Sea Stack

A steep pillar of rock located in the ocean a short distance from the coastline. These landforms are created when waves erode through a thin headland from both sides.

Seaward

Positioned or located away from land but towards an ocean or sea.

Seawater

The mixture of water and various dissolved salts found in the world's oceans and seas.

Secondary Carnivore

See tertiary consumer.

Secondary Consumer

Organisms that occupy the third trophic level in the grazing food chain. These organisms are carnivores. Also known as a primary carnivore.

Secondary Pollutant

Atmospheric pollutants that are created chemically in the atmosphere when primary pollutants and other components of the air react. Also see primary pollutant.

Secondary Substance

Organic chemical produced by a plant that has no direct function in its metabolism. Many of these chemicals are toxic and are believed to be created by the plant to reduce herbivore damage or the negative effects of competition by other plants.

Secondary Succession

Succession on a previously vegetated surface. The soil or substrate on this location contains an active seed bank.

Secondary Wave

See S-wave or shear wave.

Second-Growth Forest

Stand of forest that is the result of secondary succession.

Second Law of Thermodynamics

This law states that heat can never pass spontaneously from a colder to a hotter body. As a result of this fact, natural processes that involve energy transfer must have one direction, and all natural processes are irreversible. This law also predicts that the entropy of an isolated system always increases with time.

Sedge

Grass-like plant that is adapted to grow in moist habitats.

Sediment

Solid material that has been or is being eroded, transported, and deposited. Transport can be due to fluvial, marine, glacial or aeolian agents.

Sedimentary Rock

Rocks formed by the deposition, alteration and/or compression, and lithification of weathered rock debris, chemical precipitates, or organic sediments. Also see clastic vs non-clastic sedimentary rocks.

Sediment Rating Curve

Numerical expression or graphical curve that describes the quantitative relationship between stream discharge and the sediment transported by a particular stream.

Seed

Fertilized ovule of a plant that contains an embryo and food products for germination. Once germinated, the embryo can grow into a mature individual.

Seed Bank

Collection of seeds available for germination in the soil.

Seed Dispersal

Movement of a plant seed away from the parent plant by a passive or active mechanism.

Seepage

(1) The gradual movement of water into the soil layer.

(2) Slow movement of sub-surface water to the surface. This flow is not great enough to call it a spring.

Seepage Lake

A lake that gets its water primarily from the seepage of groundwater.

Segregated Ice

A form of periglacial ground ice that consists of almost pure ice that often exists as an extensive horizontal layer. The ice layer grows because of the active migration of water from around the feature. These features are found just below the active layer.

Seif

(1) A large sand dune that is elongated in the general direction of the dominant winds.

(2) A sand dune formed by winds from multiple directions.

Seismic

Shaking displacement usually caused by an earthquake.

Seismic Wave

Successive wave-type displacement of rock usually caused by an earthquake.

Seismograph

Instrument that measures the energy contained in seismic waves from an earthquake or other type of ground displacement.

Seismology

A branch of science focused on the study of earthquakes and seismic activity.

Self-Regulation

The ability of some systems to maintain a steady state equilibrium through positive and negative feedbacks.

Semi-Diurnal Tide

Tides that have two high and two low waters per tidal period.

Sensible Heat

Heat that can be measured by a thermometer and thus sensed by humans.

Sensible Heat Flux

Process where excess heat energy is transferred into the atmosphere. The process first involves the movement of heat energy from the Earth's surface to the atmosphere by conduction and convection. The heat energy then can move horizontally advection (atmospheric circulation).

Sexual Reproduction

Any process of reproduction that does involve the fusion of gametes.

Shale

Fine grained sedimentary rock composed of lithified clay particles.

Shear Stress

Stress caused by forces operating parallel to each other but in opposite directions.

Shear Wave

A seismic wave that creates wave-like motion perpendicular to the direction of seismic energy propagation. Also called S-wave.

Sheet Flow

See overland flow.

Sheeting

A form of physical weathering of rock where surface sheets of material fracture and exfoliate because of pressure release. Also see exfoliation dome.

Sheetwash

The removal of loose surface materials by overland flow. Process of erosion.

Shield

A large stable area of exposed very old (more than 600 million years) igneous and metamorphic rock found on continents. This rock forms the nucleus of the continents.

Shield Volcano

Volcano created from alternate layers of lava flows. Shield volcanoes are slightly sloping having a gradient between 6 and 12°. Their height can be as high as 9000 meters. The chemistry of the magma of these volcanoes is basaltic.

Shore

The land area bordering a relatively large water body like a lake or ocean.

Shoreline

The line that separates a land surface from a water body. Also see coastline.

Short Wave

A small wave in the polar jet stream and the westerlies that extends from the middle to the upper troposphere. Often associated with the formation of a mid-latitude cyclone at the ground surface. Contrasts with long waves.

Shortwave Radiation

Electromagnetic radiation with a wavelength between 0.1 and 0.7 micrometers (µm). Commonly used to describe the radiation emitted from the sun.

Shrub

A woody plant species that is smaller than a tree. Shrubs usually do not have a trunk.

Sial Layer

The part of the crust that forms the continents and is composed of relatively light, granitic rocks.

Siberian High

High pressure system that develops in winter over northern central Asia.

Sidereal Day

Time it takes to complete one Earth rotation relative to the position of a fixed star. This measurement takes 23 hours, 56 minutes, and 4.09 seconds. Compare with mean solar day.

Silica

Mineral that is composed of silicon dioxide, SiO₂.

Silicate

Group of minerals that have crystal structures based on a silica tetrahedron (SiO₄).

Silicate Magma

Magma that is felsic in composition.

Silcretes

Sedimentary rock created by the chemical precipitation of silica.

Sill

Horizontal planes of igneous rock that run parallel to the grain of the original rock deposits.They form when magma enters and cools in bedding planes found within the crust. Also see intrusive igneous rock.

Silt

Mineral particle with a size between 0.004 and 0.06 millimeters in diameter. Also see clay and sand.

Siltstone

Fine grained sedimentary rock composed of lithified silt particles.

Silurian

Geologic period that occurred roughly 408 to 438 million years ago. During this period, the first plant and insect species appear.

Sima Layer

The part of the crust that forms the ocean basins and lower layers in the crust and is composed of relatively heavy, basaltic rocks.

Sink

(1) Site of the storage of some material.

(2) Another name for sinkhole.

Sinkhole

A pit like hole in found in areas of karst. These features are caused by the weathering of limestone or dolomite by subsurface drainage. Also called a sink or doline.

Sinusoidal Equal-Area Projection

Map projection that represents areas in their true form on a two-dimensional map. Distances are only correct along parallels and central meridian. Shapes become more distorted away from the central meridian and close to the poles.

Slaking

See wetting and drying.

Slate

A fine grained metamorphic rock with well developed bedding planes derived from the slight recrystrallization of shale.

Sleet

See ice pellets.

Sling Psychrometer

Psychrometer that uses a rotating handle and a whirling motion to ventilate its wet-bulb thermometer.

Slip-Face

The lee side of a dune where material accumulates and slides or rolls downslope.

Slope Aspect

Main compass direction (North, North East, East, South East, South, South West, West, and North West) that a slope faces.

Slope Failure

The downslope movement of soil and sediment by processes of mass movement.

Slump

See rotational slip.

Small Circle

A circle on the globe's surface that does not bisect the center of the Earth. Parallels of latitude are examples of small circles.

Smog

Generic term used to describe mixtures of pollutants in the atmosphere. Also see industrial smog and photochemical smog.

Snout

Front end of a glacier. Also called the terminus.

Snow

Type of precipitation that forms in air with temperatures below freezing. Snow forms when water vapor deposits directly as a solid on a deposition nuclei, by passing the liquid state. A snowflake forms first as a very tiny crystal developing on a six-sided hexagonal deposition nuclei. The ice crystal then grows fastest at the six points as these area are more directly exposed to the atmosphere's water vapor. Snow is most common in winter just north of the center of mid-latitude cyclones. As the warm moist air travels around the center of lowest pressure, it overrides colder air located north of the low and is cooled to its saturation temperature, producing rainfall and snow. Snow generally occurs with east winds, since the winds at locations north of a mid-latitude cyclone are from the east.

Snowfield

An area of permanent snow accumulation. Usually at high altitudes or latitudes.

Snow Line

Altitudinal or latitudinal limit separating zones where snow does not melt during the summer season from areas in which it does. Similar to the concept of firm limit except that it is not limited to glaciers.

Snow Melt

Conversion of snow into runoff and groundwater flow with the onset of warmer temperatures.

Snow Pellets

Type of precipitation. Snow pellets are white, spherical grains of ice 2 to 5 millimeters in diameter. They can be distinguished from packed snowflakes since snow pellets are firm enough to bounce when they hit the ground. Snow pellets develop as supercooled droplets freeze on ice crystals. They may fall for a brief period as the precipitation changes from ice pellets to snow.

Soil

Layer of unconsolidated material found at the Earth's surface that has been influenced by the soil forming factors: climate, relief, parent material, time, and organisms. Soil normally consists of weathered mineral particles, dead and living organic matter, air space, and the soil solution.

Soil Colloids

Very small organic and inorganic particles found in a soil. Inorganic colloids are often clay particles. Soil colloids carry a negative electrical charge and are the primary sites for cation exchange. Soil colloids hold large quantities of elements and compounds which are used by plants for nutrition.

Soil Creep

Slow mass movement of soil downslope. Occurs where the stresses on the slope material are too small to create a rapid failure.

Soil Erosion

Transport of soil mineral particles and organic matter by wind, flowing water, or both. Human activities that disturb the soil surface or remove vegetation can enhance this natural process.

Soil Fertility

The ability of a soil to provide nutrients for plant growth.

Soil-Heat Flux

The rate of flow of heat energy into, from, or through the soil.

Soil Horizon

Layer within a soil profile that differs physically, biologically or chemically from layers above and/or below it.

Soil Moisture Recharge

The process of water filling the pore space found in a soil (storage).

Soil Organic Matter

Organic constituents of soil.

Soil Permeability

The rate at which water and air move vertically through a soil.

Soil Porosity

The volume of water that can be held in a soil. Also refers to the ratio of the volume of voids to the total volume of the soil.

Soil Profile

Vertical arrangement of layers or horizons in a soil.

Soil Science

The study of soils from an interdisciplinary perspective.

Soil Solution

Aqueous liquid found within a soil. This liquid normally contains ions released from mineral particles, organic matter or plant roots and leaves.

Soil Structure

General term that describes how mineral and particles organic matter of are organized and clumped together in a soil.

Soil Taxonomy

The classification of a soil in a hierarchical system based on its various properties. Grouping goes from general to specific.

Soil Texture

The relative quantities of the different types and sizes of mineral particles in a soil.

Soil Water

The water found occupying the pore spaces between soil particles.

Solar Altitude

Height of the sun above the horizon from either True North or True South.

Solar Constant

A term used to describe the average quantity of solar insolation received by a horizontal surface at the edge of the Earth's atmosphere. This value is approximately 1370 Watts per square meter.

Solar Day

Time required for the Earth to complete one rotation relative to the sun.

Solar Energy

See insolation.

Solar Noon

Point of time during the day when the sun is aligned with True North and True South.

Solar Radiation

Electromagnetic radiation that originates from the sun. Most of the sun's radiation is emitted at wavelengths between 1.0 and 0.1 microns (µm). Also see insolation, direct solar radiation, and diffused solar radiation.

Solar System

The collection of celestial bodies that orbit around the sun.

Solar Wind

Mass of ionized gas emitted to space by the sun. Plays a role in the formation of auroras.

Solar Year

The time it takes the Earth to make one orbit around the sun. This is approximately 365.2422 days.

Solid

A state of matter where molecules where the mass of the substance does not have the property of flow.

Solifluction

Form of mass movement in environments that experience freeze-thaw action. It is characterized by the slow movement of soil material downslope and the formation of lobe-shaped features. Also see gelifluction.

Solonetzic Soil

Soil order (type) of the Canadian System of Soil Classification. This soil type is associated with grassland habitats where high levels of evapotranspiration cause the accumulation of salts at or near the soil surface. These soils are common in the dry regions of the prairies where evapotranspiration greatly exceeds precipitation input.

Solstice

Dates when the declination of the sun is at 23.5° North or South of the equator. For the Northern Hemisphere this date falls on June 21 or 22 (Summer Solstice). In the Southern Hemisphere the date is December 21 or 22 (Winter Solstice).

Solum

Part of the soil that is capable of supporting life.

Solution

(1) Form of chemical weathering where rocks and minerals are dissolved by water. Materials entering the mixture can alter the chemical nature of the solution and can increase the strength of this weathering agent. For example, the mixing of carbon dioxide and water can form carbonic acid.

(2) The dissolving of a substance into a liquid.

Source Region

Area where air masses originate and come to possess their moisture and temperature characteristics.

Southeast Trade Winds

See trade winds.

Southern Oscillation

Reversal of atmospheric circulation in tropical Pacific Ocean that triggers the development of an El Nino.

South Magnetic Pole

Location in the Southern Hemisphere where the lines of force from Earth's magnetic field are vertical. This point on the Earth gradual changes its position with time.

South Pole

Surface location defined by the intersection of the polar axis with Earth's surface in the Southern Hemisphere. This location has a latitude of 90° South.

Space

(1) A distance, area, or volume.

(2) An infinite three-dimensional area in which objects have relative coordinates to each other.

(3) The region beyond the outer limits of the Earth's atmosphere.

Spatial Analysis

The examination of the spatial pattern of natural and human-made phenomena using numerical analysis and statistics.

Spatial Isolation

Reproductive isolation of two or more populations of a species by distance or physical barriers. Over long periods of time geographic isolation leads to speciation through divergent evolution because of environmental heterogeneity. Also called geographic isolation.

Spatial Tradition

Academic tradition in modern Geography that investigates geographic phenomena from a strictly spatial perspective.

Specialist Species

Species that have a relatively narrow ecological niche. These species may be able to live in only one type of habitat, tolerate only specific environmental conditions, or use only a few types of food.

Speciation

The process by which new species originate through mutations, natural selection, and evolution.

Species

(1) The different kinds of organisms found on the Earth as defined by taxonomic and/or phylogenic classification.

(2) A group of interbreeding organisms that do not ordinarily breed with members of other groups.

Species Association

A particular grouping of species in an area.

Species Diversity

See diversity.

Specific Gravity

The ratio of the mass of a body to the mass of an identical volume of water at a specific temperature.

Specific Heat

Is the heat capacity of a unit mass of a substance or heat needed to raise the temperature of 1 gram (g) of a substance 1 degree Celsius.

Specific Humidity

Measurement of atmospheric humidity. Specific humidity is the mass of water vapor in a given mass of air. Normally expressed in grams of water vapor per kilogram of air at a specific temperature.

Spectrum

Is a graph that describes the quantity of radiation that is emitted from a body at particular wavelengths.

Speed of Light

Velocity of light in a vacuum. This velocity is approximately 3 x 10⁸ meters per second. It takes light from the sun 8 minutes and 20 seconds to reach the Earth.

Spheroidal Weathering

A type of below ground chemical weathering where the corners of jointed rocks become rounded over time. Rock changes from a rectangular to more round shape.

Spit

A long and narrow accumulation of sand and/or gravel that projects into a body of ocean water. These features form as the result of the deposition of sediments by longshore drift.

Spodosols

Soil order (type) of the United States Natural Resources Conservation Service Soil Classification System. A spodosol soil has pronounced layers of illuviation characterized by accumulations of iron and aluminum oxides in the B horizon. These soils form in moist, cool climates.

Sporadic Permafrost

Form of permafrost that exists as small islands of frozen ground in otherwise unfrozen soil and sediments.

SPOT (Centre National d'Etudes Spatiales)

Series of satellites developed by the French Space Agency, with the cooperation with Belgium and Sweden for the purpose of remotely monitoring resources on the Earth. The first SPOT satellite was launched in 1986. See the following website for more information - SPOT Image.

Spring

(1) Season between winter and summer. Astronomically it is the period from the vernal equinox to the summer solstice in the Northern Hemisphere.

(2) A natural flow of water from the sub-surface to the surface. Usually occurs when the water table intersects the Earth's surface.

Spring Tide

Tide that occurs every 14 to 15 days and coincides with the new and full moon. This tide has a large tidal range because the gravitational forces of the moon and sun are complementary to each other. Contrasts with neap tide.

Squall Line

A band of thunderstorm development found ahead of a cold front.

Stability

The capability of a system to tolerate or recover from disturbance or an environmental stress.

Stable Atmosphere

Condition in the atmosphere where isolated air parcels have a tendency to sink. The parcels of air tend to be cooler than the air that surrounds them.

Stable Equilibrium

In a stable equilibrium the system displays tendencies to return to the same equilibrium after disturbance.

Stadial Moraine

See recessional moraine.

Stage

The elevation of the water surface in a stream channel.

Standard Atmospheric Pressure

A pressure of 101.32 kilopascals or 1013.2 millibars.

Standard Deviation

A statistical measure of the dispersion of observation values in a data set. Calculated by determining the square root of the variance.

Star

A large and very massive, self-luminous celestial body of gas that illuminates via the radiation derived from its internal source of energy.

Starch

Complex carbohydrate composed of thousands of glucose units. Main compound that plants use to store their food energy.

State of Matter

Form of matter. Matter can exist in three different forms gas, liquid, and solid.

Static Equilibrium

Static equilibrium occurs where force and reaction are balanced and the properties of the system remain unchanged over time.

Stationary Front

A transition zone in the atmosphere where there is little movement of opposing air masses and winds blow towards the front from opposite directions.

Steady State Equilibrium

In this type of equilibrium the average condition of the system remains unchanged over time.

Steam Fog

See evaporation fog.

Stemflow

Is the process that directs precipitation down plant branches and stems. The redirection of water by this process causes the ground area around the plant's stem to receive additional moisture. The amount of stemflow is determined by leaf shape and stem and branch architecture. In general, deciduous trees have more stemflow than coniferous vegetation.

Stephan-Boltzmann Law

This radiation law suggests the amount of radiation given off by a body is proportional to the 4th power of its temperature as measured in Kelvin units. This law can be expressed by the following simple equation:

E* = sT ⁴

where E* is the amount of radiation emitted by the body in Watts per square meter,

s is a constant equal to 0.0000000567,

and T is the temperature of the body in Kelvins.

Steppe

Russian term for mid-latitude grasslands.

Stoma (pl. Stomata)

Small opening on the surface of a plant that is used for gas exchange.

Storm Surge

Relatively rapid rise in the height of the ocean along a coastline. Often caused by the storm winds pushing water towards land.

Storm Track

The path taken by a storm (thunderstorm, mid-latitude cyclone or hurricane) or the average path taken by storms.

Stoss

Side of a slope that faces the direction of flow of ice, wind, or water. Opposite of lee.

Stratified Drift

A type of glacial drift that has been partially sorted by glaciofluvial meltwater.

Strata

The layers or beds found in sedimentary rock.

Stratigraphy

Subdiscipline of geology that studies sequence, spacing, composition, and spatial distribution of sedimentary deposits and rocks.

Stratocumulus Clouds

Low altitude gray colored cloud composed of water droplets that has a patchy appearance. Each cloud patch consists of a rounded mass. This cloud has a somewhat uniform base and normally covers the entire sky. Between the patches blue sky can be seen. Found in an altitude range from the surface to 3,000 meters.

Stratopause

The stratopause is a relatively thin atmospheric transition layer found between the stratosphere and the mesosphere. The height of this layer is about 50 kilometers above the Earth's surface.

Stratosphere

Atmospheric layer found at an average altitude of 11 to 50 kilometers above the Earth's surface. Within the stratosphere exists the ozone layer. Ozone's absorption of ultraviolet sunlight causes air temperature within the stratosphere to increase with altitude.

Stratovolcano

See composite volcano.

Stratus Clouds

Low altitude gray colored cloud composed of water droplets. This cloud has a uniform base and normally covers the entire sky. It is also quite thick and can obscure the sun. Light precipitation is often found falling from it. Found in an altitude range from the surface to 3,000 meters.

Stream

A long narrow channel of water that flows as a function of gravity and elevation across the Earth's surface. Many streams empty into lakes, seas or oceans.

Stream Bank

Sides of the stream channel.

Stream Bed

Bottom of the stream channel.

Stream Channel

Long trough-like depression that is normally occupied by the water in a stream.

Stream Discharge

A river or stream's rate of flow over a particular period of time. Usually measured by a current meter and expressed in cubic meters per second. Stream discharge depends on the volume and velocity of the flow.

Stream Flow

The flow of water in a river or stream channel.

Stream Gradient

The change in elevation from a stream's headwaters to its mouth expressed in degrees, percentage, or as a distance ratio (rise/run).

Stream Load

Refers to the material or sediment carried by a stream. In normally consists of three components: bed load (pebbles and sand which move along the stream bed without being permanently suspend in the flowing water), suspended load (silts and clays in suspension) and dissolved load (material in solution).

Stream Order

The relative position, or rank, of a stream channel segment in a drainage network.

Stream Long Profile

Vertical and horizontal profile of the stream. Most streams have a profile that is concave shaped.

Striations

Grooves of scratches found in surface rock that are the result of glacial abrasion.

Strike

One of the directional properties of a geologic structure such as a fold or a fault. Strike is the horizontal directional taken by an imaginary line drawn on the plane of the formation. Also see dip.

Strike-Slip Fault

Fault that primarily displays horizontal displacement.

Structural Landform

Is a landform created by massive Earth movements due to plate tectonics. This includes landforms with some of the following geomorphic features: fold mountains, rift valleys, and volcanoes.

Subatomic Particles

Extremely small particles that make up the internal structure of atoms.

Subduction (Tectonic)

Process of plate tectonics where one lithospheric plate is pushed below another into the asthenosphere.

Subduction Zone

Linear area where tectonic subduction takes place.

Sublimation

Process where ice changes into water vapor without first becoming liquid. This process requires approximately 680 calories of heat energy for each gram of water converted.

Submarine Canyon

V-shaped canyons cut into the continental slope to a deep of up to 1200 meters. These features are normally associated with major rivers.

Subpolar Glacier

Glacier in which the ice found from the its surface to base has a temperature as cold as -30° Celsius throughout the year. This is well below the pressure melting point. However, melting does occur in the accumulation zone in the summer. One of the three types of glaciers: cold glacier; temperate glacier; and subpolar glacier.

Subpolar Lows

Surface zone of atmospheric low pressure located at about 60° North and South latitude. These low pressure systems are produced by the frontal lifting of subtropical air masses over polar air.

Subsea Permafrost

Form of permafrost that exists beneath the sea in ocean sediments.

Subsidence

Lowering or sinking of the Earth's surface.

Subsolar Point

The location on the Earth where the sun is directly overhead. Also see declination.

Subtropical High Pressure Zone

Surface zone of atmospheric high pressure located at about 30° North and South latitude. These high pressure systems produced by vertically descending air currents from the Hadley cell.

Subtropical Jet Stream

Relatively fast uniform winds concentrated within the upper atmosphere in a narrow band. The subtropical jet stream exists in the subtropics at an altitude of approximately 13 kilometers. This jet stream flows from west to east and has a speed that is somewhat slower that the polar jet stream. Also see jet stream.

Succession

Directional cumulative change in the types plant species that occupy a given area, through time.

Succulent Vegetation

Group of plants that have the ability to survive in deserts and other dry climates by having no leaves. Instead their branches and stems that are photosynthetic. This adaptation reduces the surface area for evaporation thus reducing the loss of scarce water.

Sugar

Type of carbohydrate chemically based on carbon, oxygen, and hydrogen.

Sulfur Dioxide

A gas produced from volcanic eruptions, ocean spray, organic decomposition and the burning of fossil fuels. Sulfur dioxide is a component in the creation of acid precipitation. This colorless gas has the chemical formula SO₂.

Sulfate Aerosol

Type of solid compound commonly found in the atmosphere. These particles play an important role in reflecting, absorbing, and scattering incoming insolation. The source of these compounds is both natural and human-made. Most of the human-made particles come from the combustion of fossil fuels.

Sulfuric Acid

Acid with the chemical formula H₂SO₄.

Summer

Season between spring and fall. Astronomically it is the period from the summer solstice to the autumnal equinox in the Northern Hemisphere.

Summer Solstice

Date when the declination of the sun is at 23.5° North of the equator. This date is usually June 21 or 22.

Sun

Luminous star around which the Earth and other planets revolve around. The sun emits 63,000,000 Watts per square meter of electromagnetic radiation. The sun has an average distance from the Earth of about 150,000,000 kilometers. The Earth's orbit is not circular but elliptical.

Sunrise

Moment of time when the sun's edge first appears above the Earth's horizon.

Sunset

Moment of time when the sun's edge completely disappears below the Earth's horizon.

Sunspot

Dark colored region on the sun that represents an area of cooler temperatures and extremely high magnetic fields.

Supercooled Water

Cooling of water below 0° Celsius without freezing. Common in clouds where there is a deficiency of condensation nuclei.

Super-Saturation

Atmospheric condition where saturation occurs at a relative humidity greater than 100 % because of a shortage of deposition or condensation nuclei.

Surface Heat Flux

Process where excess heat energy is transferred into the ground.

Surface Creep

The sliding and rolling movement of soil particles on the Earth's surface because of wind. Eolian process of soil particle movement.

Surface Tension

Tension of a liquid's surface. Due to the forces of attraction between molecules.

Surface Wave

Type of seismic wave that travels across the Earth's surface. These earthquake generated waves cause the Earth's surface to roll or sway like waves on the ocean.

Surge

A large, destructive ocean wave caused by very low atmospheric pressure and strong winds. Hurricanes often cause a surge of the ocean surface.

Suspended Load

Portion of the stream load that is carried almost permanently suspended in flowing water.

Suspension

Erosional movement of sediment continually held in the transport medium of air, water or ice.

Sustainable Development

Forms of economic growth and other human activities that meet the requirements of the present without jeopardizing the ability of future generations of individuals to meet their own needs.

Swash

A thin sheet of water that moves up the beach face after a wave of water breaks on the shore.

S-Wave

A seismic wave that moves material it encounters perpendicular to its direction of travel. This type of seismic wave causes shear stress in the material it moves through. Also called a secondary wave or a shear wave.

Swell

A relatively smooth ocean wave that travels some distance from the area of its generation.

Symbiotic

Mutual relationship between two organisms which is necessary for either to survive.

Symbiotic Mutualism

Mutualistic interaction where the species interact physically and their relationship is biologically essential for survival.

Syncline

A fold in rock layers that forms a trough-like bend.

Synoptic Scale

Scale of geographic coverage used on daily weather maps to describe large scale atmospheric phenomenon (for example, mid-latitude cyclone, air masses, fronts, and hurricanes).

System

A system is a set of interrelated components working together towards some kind of process.

System Attribute

A system attribute is the perceived characteristic of a system element. For example, number, size, color, volume, and temperature may be some of the perceived characteristics of clouds in the atmospheric system.

System Boundary

Outer edge of system. Zone between one system and another system.

System Element

System elements are the kinds of things or substances composing the system. They may be atoms or molecules, or larger bodies of matter-sand grains, rain drops, plants, or cows.

System Relationship

Is the association that exist between the elements and attributes of a system based on cause and effect.

System State

Current value of a system's elements, attributes, and/or relationships.