Earth system science(1)

An integrated approach to the study of the Earth that stresses investigations of the interactions among the Earth's components in order to explain Earth dynamics. evolution. and global change.

Earth system(1)

The Earth regarded as a unified system of interacting components. including geosphere (land). atmosphere (air). hydrosphere (water and ice). and biosphere (life).


The amount that the earth's revolution deviates from a circular path. the variation of an ellipse from a circle. where a circle has an eccentricity of 0.


A small volume of air (or any fluid) that behaves differently from the larger flow in which it exists.

Effective emissivity(6)

A correction factor. dependent on the radiational characteristics of the earth-atmosphere system. that permits application of black body radiation laws to the earth-atmosphere system

El Ni�o(2)

The appearance of unusually warm waters in the eastern Pacific. termed the 'Christ child.' because of the time of year it effects the South American coastline.

Electromagnetic radiation(1)

Energy propagated as time-varying electric and magnetic fields. These two fields are inextricably linked as a single entity since time-varying electric fields produce time-varying magnetic fields and vice versa. Light and radar are examples of electromagnetic radiation differing only in their wavelengths (or frequency). Electric and magnetic fields propagate through space at the speed of light.


The fractional amount of radiation emitted by a given object or substance in comparison to the amount emitted by a perfect emitter.


The rate at which a black body radiates energy across all wave-lengths.

Energy budget(1)

A quantitative description of the energy exchange for a physical or ecological system. The budget includes terms for radiation. conduction. convection. latent heat. and for sources and sinks of energy.

Enhanced Greenhouse Effect(5)

The increase in the natural greenhouse effect resulting from increases in atmospheric concentrations of GHGs due to emissions from human activities.


The mixing of environmental air into a preexisting air current or cloud so that the environmental air becomes part of the current or cloud.

Environmental lapse rate(6)

The rate of decrease of temperature with elevation. It is most often measured with a radiosonde.

Equilibrium vapor pressure(6)

The necessary vapor pressure around liquid water that allows the water to remain in equilibrium with its environment. Also called saturation vapor pressure.


The time when the sun crosses the plane of the earth's equator occurring about March 21 and September 22.

Evaporation fog(6)

Fog produced when sufficient water vapor is added to the air by evaporation. The two common types are steam fog. which forms when cold air moves over warm water. and frontal fog. which forms as warm raindrops evaporate in a cool air mass.


The physical process by which a liquid or solid is changed to a gas. the opposite of condensation.


The sum of evaporation and plant transpiration. Potential evapotranspiration is the amount of water that could be evaporated or transpired at a given temperature and humidity. if there was plenty of water available. Actual evapotranspiration can not be any greater than precipitation. and will usually be less because some water will run off in rivers and flow to the oceans. If potential evapotranspiration is greater than actual precipitation. then soils are extremely dry during at least a major part of the year.

Excessive Heat Outlook(3)

This CPC product. a combination of temperature and humidity over a certain number of days. is designed to provide an indication of areas of the country where people and animals may need to take precautions against the heat during May to November.


The outermost portion of the atmosphere.


In meteorology. the area north of the Tropic of Cancer and the area south of the Tropic of Capricorn. In other words. the area outside the tropics


Temperature scale designed by the German scientist Gabriel Fahrenheit in 1709. based upon water freezing at 32�F and water boiling at 212�F under standard atmospheric pressure. Compare with centigrade.

Fall Freeze date(6)

The date of occurrence in the fall of the first minimum at or below a temperature threshold.

Fall streaks(6)

Falling ice crystals that evaporate before reaching the ground.


the measure of the flow of some quantity per unit area per unit time.


See Chinook.


A cloud with its base at the earth's surface. It reduces visibility to below 1 km.

Forced convection(6)

On a small scale. a form of mechanical stirring taking place when twisting eddies of air are able to mix.

Forcing Mechanism(4)

A process that alters the energy balance of the climate system. i.e. changes the relative balance between incoming solar radiation and outgoing infrared radiation from Earth. Such mechanisms include changes in solar irradiance. volcanic eruptions. and enhancement of the natural greenhouse effect by emission of carbon dioxide. See radiation. infrared radiation. radiative forcing.


A weather forecast. or prediction. is an estimation based on special knowledge of the future state of the atmosphere with respect to temperature. precipitation. and wind. Weather forecasts are now routinely provided for up to 14 days in advance and outlooks for seasonal and longer timescales. (Synonymous with predictions and outlooks).

Free convection(6)

Convection triggered by intense solar heating of the earth's surface.

Freeze free season(6)

The number of days between the last spring freeze date and the first fall freeze date.


A condition occurring over a widespread area when the surface air temperature remains below freezing for a sufficient time to damage certain agricultural crops. A freeze most often occurs as cold air is advected into a region. causing freezing conditions to exist in a deep layer of surface air. Also called advection frost.

Freezing rain and freezing drizzle(6)

Rain or drizzle that falls in liquid form and then freezes upon striking a cold object or ground. Both can produce a coating of ice on objects which is called glaze.


The transition zone between two distinct air masses.

Frontal fog(6)

See Evaporation fog.

Frost (also called hoarfrost)(6)

A covering of ice produced by deposition (sublimation) on exposed surfaces when the air temperature falls below the frost point (the dew point is below freezing).

Frost point(6)

See Dew point.

Frozen dew(6)

The transformation of liquid dew into tiny beads of ice when the air temperature drops below freezing.

Funnel cloud(6)

A rotating conelike cloud that extends down-ward from the base of a thunderstorm. When it reaches the surface it is called a tornado.

Gaia hypothesis(1)

The hypothesis that the Earth's atmosphere. biosphere. and its living organisms behave as a single system striving to maintain a stability that is conductive to the existence of life.

General Circulation Model (GCM)(1)

A global. three-dimensional computer model of the climate system which can be used to simulate human-induced climate change. GCMs are highly complex and they represent the effects of such factors as reflective and absorptive properties of atmospheric water vapor. greenhouse gas concentrations. clouds. annual and daily solar heating. ocean temperatures and ice boundaries. The most recent GCMs include global representations of the atmosphere. oceans. and land surface.

Geologic time scale(2)

Relative time scale based onstratigraphic position and correlation. and many different types of chronologic evidence. Geologic time is broken down into eons. eras. periods and epochs.

Geostrophic wind(6)

A theoretical horizontal wind blowing in a straight path. parallel to the isobars or contours. at a constant speed. The geostrophic wind results when the Coriolis force exactly balances the horizontal pressure gradient force.

Glaciated cloud(6)

A cloud or portion of a cloud where only ice crystals exist.


The conversion of all the supercooled liquid water in a cloud into ice crystals. thus reducing the growth rate of ice crystals and hail.


River of ice that under pressure can deform and flow plastically.


A coating of ice on objects formed when supercooled rain freezes on contact. A storm that produces glaze is called an icing storm.

Global carbon budget(1)

The balance of the exchanges (incomes and losses) of carbon between the carbon reservoirs or between one specific loop (e.g.. atmosphere biosphere) of the carbon cycle. An examination of the carbon budget of a pool or reservoir can provide information about whether the pool or reservoir is functioning as a source or sink for CO2.

Global climate change(6)

The long-term fluctuations in temperature. precipitation. wind. and all other aspects of the Earth's climate. External processes. such as solar-irradiance variations. variations of the Earth's orbital parameters (eccentricity. precession. and inclination). lithosphere motions. and volcanic activity. are factors in climatic variation. Internal variations of the climate system also produce fluctuations of sufficient magnitude and variability to explain observed climate change through the feedback processes interrelating the components of the climate system.
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Americans’ health, security and economic wellbeing are tied to climate and weather. Every day, we see communities grappling with environmental challenges due to unusual or extreme events related to climate and weather. In 2011, the United States experienced a record high number (14) of climate- and weather-related disasters where overall costs reached or exceeded $1 billion. Combined, these events claimed 670 lives, caused more than 6,000 injuries, and cost $55 billion in damages. Businesses, policy leaders, resource managers and citizens are increasingly asking for information to help them address such challenges.