S - U

S

Saturation vapor pressure The maximum amount of water vapor necessary to keep moist air in equilibrium with a surface of pure water or ice. It represents the maximum amount of water vapor that the air can hold at any given temperature and pressure. (See Equilibrium vapor pressure.)

Sea level pressure The atmospheric pressure at mean sea level. 
Simulation The highly abstract forms of real systems which are totally mathematical and computerised and are hyothetical in nature.

Smog Originally smog meant a mixture of smoke and fog. Today, smog means air that has restricted visibility due to pollution, or pollution formed in the presence of sunlight-photochemical smog.

Solstice Either of the two times of the year when the sun is the greatest distance from the celestial equator, occurring about June 22 and December 22. See winter solstice and summer solstice. 
Species A group of living organisms having similar structure, function and behaviour with a common ancestory and share a common gene pool.

Specific heat The ratio of the heat absorbed (or released) by the unit mass of the system to the corresponding temperature rise (or fall).

Specific humidity The ratio of the mass of water vapor in a given parcel to the total mass of air in the parcel.

Spontaneous nucleation (freezing) The freezing of pure water without the benefit of any nuclei.
Standing Crop It is the amount of living material present in different trophic levels or in a component population. This term is applicable to both plants as well as animals.
Standing State The amount of inorganic substances like P, C, N, S, H etc. present at any given time in an ecosystem is known as Standing state or Standing Quality.

Steppe One of the two types of dry climate. A marginal and more humid variant of the desert that separates it from bordering humid climates. Steppe also refers to the short-grass vegetation associated with this semiarid climate.

Storm surge An abnormal rise of the sea along a shore. Primarily due to the winds of a storm, especially a hurricane.

Stratocumulus A low cloud, predominantly stratiform with low, lumpy, rounded masses, often with blue sky between them.

Stratopause The boundary between the stratosphere and the mesosphere.

Stratosphere The layer of the atmosphere above the troposphere and below the mesosphere (between 10 km and 50 km), generally characterized by an increase in temperature with height.

Stratus A low, gray cloud layer with a rather uniform base whose precipitation is most commonly drizzle.

Sublimation The process whereby ice changes directly into water vapor without melting. In meteorology, sublimation can also mean the transformation of water vapor into ice. (See Deposition.)

Subsidence The slow sinking of air, usually associated wit high-pressure areas.

Subsidence inversion A temperature inversion produced by the adiabatic warming of a layer of sinking air.

Summer solstice Approximately June 22 in the Northern Hemisphere when the sun is highest in the sky and directly overhead at latitude 23.5º N, the Tropic of Cancer.

Supersaturated air A condition that occurs in the atmosphere when the relative humidity is greater that 100 percent. 
System A system is defined as a holistic unit made up of a no interdependent and interlinked subcomponents which operate by receiving certain input and giving some output by utilising the input for some transformations.
1. Open system- An Aquarium
2. Closed system- Dark caves
Systems Analysis Steps- 1. the physical observations are converted in to logical statements.
2. the characters of a real system are deducted from the from the properties of the model.
3.  Future interactions are controlled by utilising the parameters of the model. 
System Ecology Application or principles and methods of system approach for studies in ecology".
System Theory This theory propounds that every object or organism has two environments i.e. input and output which are inseparable from the organism.
 

T

Temperature inversion An extremely stable air layer in which temperature increases with altitude, the inverse of the usual temperature profile in the troposphere.

Thermosphere The atmospheric layer above the mesosphere. It extends from 90 km to outer space.

Trade winds The winds that occupy most of the tropics and blow from the subtropical highs to the equatorial low. 
Trophic Level The various steps through which food energy passes in an ecosystem is known as trophic level.
or
A functional grouping of organisms based on similar mode of nutrition. 

Troposphere The layer of the atmosphere extending from the earth's surface up to the tropopause (about 10 km above the ground).

Turbulence Any irregular or disturbed flow in the atmosphere that produces gusts and eddies.