En-Ez

 

ENAM

Acronym for European North Atlantic Margin, a series of projects to quantify and model large-scale sedimentary processes and fluxes in the named area. See the ENAM Web site.

 

enclave

A low-lying region that is free of ice during a glacial stage. Constrast with nunatak.

 

energy balance model

A simple class of climate models (abbreviated as EBM) that focuses on the required balance between incoming and outgoing radiation at the top of the atmosphere. EBMs are solely thermodynamic and include no dynamics or moisture processes and as such calculate only one dependent variable, the temperature. Nonetheless, the temperature fields calculated using 2-D EBMs agree well with both observations and fields calculated using more complex general circulation model. See Crowley and North (1991) and North et al. (1981).

 

ENPCW

See Eastern North Pacific Central Water.

 

ENRICH

Acronym for the European Network for Research in Global Change, the objective of which is to pursue a major coherent European contribution to international actions on global change research. See the ENRICH Web site.

 

ensemble

The collection of all possible realizations of a stochastic process.

 

ENSO

See El Nino/Southern Oscillation.

 

enstrophy

This is defined as half of the area-mean vorticity squared in a fluid, mathematically expressed by

where A is the area over which the calculation is being made and the vorticity. The relation between vorticity and enstrophy is similar to that between velocity and kinetic energy, and the enstrophy budget is used in the study of large-scale motions in the ocean and atmosphere as an alternative to the more cumbersome vorticity budget. See Wiin-Nielsen and Chen (1993).

 

enthalpy

The heat content per unit mass of a substance measured as the internal energy plus the product of its volume and pressure. In the atmosphere this is the sum of the sensible heat, latent heat and superheat of the vapor above the saturation or dew-point temperature.

 

entity cloud

An abstraction used in the parameterization of clouds in large-scale numerical models. This is the physical entity consisting of a part of the condensate and occupying a certain volume of air that is often only a fraction of a grid volume. See Sundqvist (1993).

 

entrainment interfacial layer

The sharp transition zone between the planetary boundary layer and the free atmosphere in the interfacial region between cloud and no-cloud in the atmosphere. The EIL can evince a temperature change of C over less than 5 m. The has also been called the entrainment zone (EZ). See Kraus and Businger (1994).

 

entrainment zone

Another name for the entrainment interfacial layer.

 

Environmental Research Laboratory

A division of the NESDIS branch of NOAA whose mission is to conduct an integrated program of fundamental research, related technology development, and services to improve understanding and prediction of the geophysical environment consisting of the oceans and inland waters, lower and upper atmosphere, the space environment, and the Earth. More information can be found at the ERL Web site.

 

Eocene

The second of five epochs in the Tertiary period, lasting from 57.8 to 36.6 Ma. It is preceded by the Paleocene epoch and followed by the Oligocene epoch.

 

EOF

Acronym for empirical orthogonal function.

 

eolian

See aeolian.

 

eon

Nothing yet.

 

EOS

Acronym for Earth Observing System, the suite of satellite sensors to be launched and managed by NASA under the Mission to Planet Earth Program in support of the U.S. Interagency Global Change Research Program (GCRP). This network of polar-orbiting and low-inclination satellites will provide global observations of the land surface, biosphere, solid Earth, atmospheres and oceans for a minimum of 15 years. See the EOS Web site, especially the EOS Reference Handbook.

 

EOSAP

Acronym for EOS Amazon Project.

 

EOSDIS

Acronym for Earth Observing System Data and Information System, the NASA infrastructure of seven DAACs which receive, process, archive, manage and distribute EOS data products among EOS investigators.

 

EOSIS

Acronym for the Earth Observing System Interdisciplinary Science project, a NASA project to improve diagnosis of global changes through the understanding of the coupled ocean-atmosphere system. The objectives are to improve existing and develop new methodologies for estimating global ocean-atmosphere fluxes in momentum, energy, water and carbon dioxide, to study the changes in the transport and storage of heat, water, and greehouse gases by the ocean in response to surface forcing, and to understand the energy and hydrologic balances of the atmosphere and their relation with ocean surface fluxes. See the EOSIS Web site.

 

EOSP

Abbreviation for Earth Observing Scanning Polarimeter, an EOS instrument planned for the AM2 and AM3 satellite platforms. It is a cross track scanning polarimeter which globally maps radiance and linear polarization of reflected and scattered sunlight for 12 spectral bands from 0.41 to 2.25 micrometers. It will provide global aerosol distribution and cloud properties such as optical thickness and phase.

 

EOSSMS

Abbreviation for EOS Space Measurement System.

 

EOWIC

Acronym for Earth Observation World Information Centre.

 

epibenthos

See benthos.

 

EPICA

Acronym for European Project for Ice Coring in Antarctica.

 

EPOCS

Acronym for the NOAA Equatorial Pacific Ocean Climate Studies program. The goal of EPOCS was to obtain the requisite knowledge of the underlying physical and thermodynamic processes in the equatorial Pacific to enable the anticipation, planning, and alleviation of adverse social and economic impacts due to short-term climate variations.

 

EPOP

Acronym for European Polar Orbiting Platform.

 

equable climates

This refers to hypothesized past warm climates lacking in extreme variations, although the viability of the concept has been called into question in light of recent modeling results concerning supercontinents. See Crowley and North (1991) section 11.2.7 and the references therein.

 

equation of mass continuity

An equation stating that because the mass of a fluid parcel is constant, the density must decrease/increase if the flow diverges/converges. This is mathematically expressed by

where is the fluid density and v the vector velocity. See Dutton (1986).

 

equatorial beta plane

An approximation for oceanic and atmospheric motions near the equator where the substitutions sin and cos are made into the governing equations of motion. In this approximation, beta is a constant given by

where is the rotation rate of the earth and r its radius, and f is given by

where is distance northward from the equator. See Hendershott (1981), p. 304 and Gill (1982), p. 434.

 

Equatorial Countercurrent

In physical oceanography, a subsurface eastward flow that is about 100-200 m thick and 200-300 km wide. It is centered approximately on the equator, and its core lies just beneath the base of the mixed layer in the top of the equatorial thermocline. Such a current is found in all three oceans, although it appears to be a seasonal phenomenon in the Indian Ocean. See Leetmaa et al. (1981).

 

equatorial radius of deformation

A form of the Rossby radius of deformation applicable to wave motions near and at the equator. It is defined as

where c is the gravity wave speed, i.e. where H is the depth (or equivalent depth). This radius is about 2000 km (c = 200 m/s) for barotropic waves in the ocean, making it marginally applicable for use with the equatorial beta plane concept. The approximation is much more valid for the case of baroclinic waves where, for typical atmosphere (20-80 m/s) and ocean (0.5-3.0 m/s) values of c, the equatorial deformation radius is, respectively, 650-1300 km and 100-250 km.

 

equatorial trough

A region of lower pressure located between the subtropical highs on each side of the equator. Within this zone the trade wind airstreams from either hemisphere meet causing ascending motion and large amounts of precipitation. It constitutes the equatorward, ascending portions of the Hadley mean meridional circulation cells of both hemispheres. Energetically this results in an import of water vapor concentrated in the trade wind layer and an export of geopotential energy and sensible heat in th eupper troposphere. This results in a net atmospheric heat export from the trough zone to the higher latitudes. This region, commonly called the doldrums, is centered near S in January and N in July. Its migration between these extremes influences the seasonal distribution of cloudiness and rainfall and the formation of tropical storms, and its annual mean position is known as the meteorological equator.

 

Equatorial Undercurrent

In physical oceanography, a subsurface eastward flow centered approximately on the equator whose core lies just beneath the base of the mixed layer in the top of the equatorial thermocline. The flow generally ranges from 100-200 m thick and 200-300 km wide. Such a current is found in all three oceans, although it appears to be a seasonal phenomenon in the Indian Ocean. In the Atlantic its core is around 100 m deep with speeds exceeding 1.2 m/s and transports up to 15 Sv. It alternates between extreme positions 90 km on either side of the Equator on a 2-3 week time scale with speed and transport fluctuating between the previous figures and 0.6 m/s and 4 Sv. In the Pacific it has a width of 400 km, a thickness of only 200 m, and typical velocities of 1.5 m/s, with the core depth ranging from 200m in the west to 40 m in the east. The details are much more complicated and less well known for the Indian Ocean, although it appears to be present primarily during the northeast monsoon.

The dynamical explanation for a an undercurrent has an appealing qualitative explanation, i.e. fluid converging towards the equator conserves absolute vorticity. As a result, relative vorticity has to increase to make up for the vanishing of planetary vorticity there, with this providing a source of eastward momentum to drive the undercurrent. The balance of forces at the equator reduces to

where p is the pressure (baroclinic), x the coordinate along the equator, the momentum diffusion coefficient, z the vertical coordinate, and u the along equator velocity component. This is a linear equation, and although the addition of nonlinearities has brought model results and observations into closer concordance, it is thought that they are not essential for maintaining the undercurrent and serve only to modify the linear dynamics. The unsteady flow represented by the dynamics of equatorial waves has also been postulated as an explanation for the observe time-varying characteristics of the undercurrent. See Philander (1973), Philander (1980), Leetmaa et al. (1981) and Tomczak and Godfrey (1994).

 

equatorially trapped gravity wave

 

equatorially trapped Kelvin wave

An equatorially trapped wave similar in character to coastally trapped Kelvin waves. The motion is unidirectional and parallel to the equator everywhere, and in each vertical plane parallel to the equator the motion is the same as for a nonrotating fluid. A required geostrophic balance between the east-west velocity and the north-south pressure gradient leads to solutions that decay away from either side of the equator on a length scale called the equatorial radius of deformation. These dispersionless waves propagate eastward at the same speed as they would in a nonrotating fluid, with the dispersion relation being . The magnitude of c for the first baroclinic mode for typical ocean values is around 2.8 m/s, which would take a Kelvin wave across the Pacific in about 2 months. See Gill (1982).

 

equatorially trapped Poincare wave

See equatorially trapped gravity wave.

 

equatorially trapped Rossby wave

 

equatorially trapped wave

A wave that is confined to propagate on and near the equator due to the local waveguide properties. The waveguide is caused by the vanishing of at the equator. This means that the conditions for geostrophic balance theoretically fail there, although practically any wave motion having a finite expanse across the equator will feel the Coriolis force on either side. This will serve to turn that motion back towards the equator on either side, thus serving as a trap or a waveguide for motions there. See Gill (1982).

 

equilibration time

The time it takes for a system to re-equilibrate after being subject to a perturbation. This is usually expressed in terms of an e-folding time. Some typical equilibration times are: the atmosphere, 11 days; the ocean mixed layer, 7-8 years; the deep ocean, 300-1000 years; mountain glaciers, 300 years; ice sheets, 3000 years; the Earth's mantle, 30 million years.

 

equilibrium tide

The hypothetical tide which would exist if the ocean responded instantly to the tide producing forces and formed an equilibrium surface. The effects of friction, inertia, and the irregular distribution of land masses are ignored.

 

equinox

One of the two days in a year (presently about March 21 and Sept. 23) when there are exactly 12 hours of day and 12 hours of night at all points on the Earth. The two points on the celestial sphere where the ecliptic intersects the celestial equator. At the vernal equinox the Sun crosses the celestial equator from south to the north, and at the autumnal equinox from north to south, with the former being the zero point in celestial coordinate systems.

 

equivalent barotropic

An atmospheric state in which the temperature gradients are such that the isotherms are parallel to the isobars.

 

equivalent carbon dioxide concentration

For a given amount of a greenhouse gas, the amount of carbon dioxide that would provide an equivalent forcing.

 

equivalent depth

When the solution of a differential equation set (e.g. the equations of motion for a baroclinic atmosphere or ocean) is approximated using the normal mode technique, each of the independent normal or baroclinic mode solutions obtained behaves equivalently to a homogeneous system with a depth that is called the equivalent depth. See Gill (1982).

 

equivalent potential temperature

In meteorology, the equivalent temperature of an air sample when it is brought adiabatically to a pressure of 1000 mb. It is a conservative property for both dry and saturated adiabatic processes.

 

equivalent temperature

The temperature that a sample of moist air would attain if all of the water vapor were condensed and the latent heat released to raise the temperature of the sample, i.e. the temperature arrived at isobarically when all the vapor in a sample is condensed. It is given by

where e is the mixing ratio, L is the appropriate latent heat, the specific heat at constant pressure, and p the atmospheric pressure.

 

ERBE

Acronym for the Earth Radiation Budget Experiment, the first multiple-satellite radiation budget experiment, which included a medium-inclination orbiter to measure diurnal variations and used a scene-dependent inversion scheme. See Barkstrom (1984) and the ERBE Web site for more details.

 

erg

The unit of work or energy in the cgs system of units. It is the work done by a force of 1 dyne in moving its point of application 1 cm in the direction of the force. Some equivalences are: 1 erg = 10 joules = 10 watt sec.

 

ergodic hypothesis

The assumption that a process is statistically stationary, and therefore ensemble averaging is equivalent to averaging over time. See Kagan (1995).

 

ERICA

Acronym for the Experiment on Rapidly Intensifying Cyclones Over the Atlantic project, a study to determine physical mechanisms and proceses which lead to explosive wintertime storms developing over the Atlantic Ocean. This is a follow-up to the GALE experiment. See the ERICA Web site.

 

ERIN

Acronym for the Australian Environmental Resources Information Network. See the ERIN Web site.

 

ERL

Acronym for the Environmental Research Laboratory.

 

ERM

Acronym for Exact Repeat Mission, a GEOSAT mission to accurately measure and calculate sea level deviations from the geoid. See Cheney et al. (1986).

 

EROS

Acronym for Earth Resources Observations System.

 

error of representativeness

The spatial spectrum of the atmosphere or ocean shows variance at all scales, with generally less variance at smaller scales. The observation network, however, has a finite spacing between observation stations. If a network has an average spacing of, say, L between stations, then samples with scales much greater or smaller will be sample, respectively, very well or very poorly by the network. For instance, a network with 1000 km spacing will not see a tornado or thunderstorm with a 10 km characteristic length scale if it is between stations, but will see it if it overlies a station and, in addition, will misrepresent it as a larger scale motion. This is occasionally known as aliasing. See Daley (1991).

 

ERS

Acronym for the Earth Resources Satellite.

 

Ertel potential vorticity

A rigorous formulation of potential vorticity for any compressible, thermodynamically active, inviscid fluid in adiabatic flow. The Ertel potential vorticity is defined by

where S is some conservative thermodynamic property of the fluid (the potential temperature, e.g.), is the angular velocity of the coordinate system, is the density, and V the velocity of the fluid relative to the coordinate system. See Muller (1995).

 

Ertel's theorem

A theorem stating that in an incompressible Boussinesq fluid that is homogeneous and inviscid a quantity called the potential vorticity is conserved. See Hide (1978).

 

ESA

Abbreviation for European Space Agency. See the ESA Web site for further information.

 

ESD

Abbreviation for the NASA/GSFC's Earth Science Directorate, whose mission is to provide leadership in achieving improved observations and understanding of global Earth systems and trends through the development and effective utilization of space technologies. See the ESD Web site for further information.

 

ESF

Abbreviation for European Science Foundation. See the ESF Web site.

 

ESPCW

See Eastern South Pacific Central Water.

 

ESRIN

Acronym for European Space Research Institute, an establishment of ESA. Its main activities are centered on the acquisition, archiving and dissemination of data from Earth Observation missions, in particular ERS-1. See the ESRIN Web site for further information.

 

ESS

Abbreviation for the Earth and Space Science project, an effort to employ advanced computers to further understanding of and ability to predict the dynamically interacting physical, chemical, and biological processes that drive these systems. It is an integral component of the NASA HPCC program, and more information can be found at the ESS Web site.

 

ESSC

Abbreviation for the Earth System Science Center, a research institute at Penn State that coordinates research related to the global water cycle, biogeochemical cycles, Earth system history, and human impacts on the Earth system. See the ESSC Web site.

 

ESSE

Abbreviation for Earth System Science Education, a project that links faculty at over 20 universities with one another and with NASA scientists to accelerate the development of undergraduate curricula in earth system science. The project objectives were to establish such a national academic forum and also to expand the interdisciplinary interests and number of future scientists who elect to pursue earth science research professionally. See the ESSE Web site.

 

estuarine Richardson number

A form of the Richardson number that gauges the relative effects of stratification and mixing in estuaries. It is given by

where is the RMS tidal velocity, W the channel width, the difference in density between river and ocean water, the average density, g gravitational acceleration and the fresh water discharge rate. If R is large the estuary will be strongly stratified the flow dominated by density currents, and if it is small the estuary will be well mixed and density effects can probably be neglected. There is also a modified version of this in which is replaced by the shear velocity to include the effect of varying bottom friction. See Fischer et al. (1979).

 

estuary

A semi-enclosed body of water having a free connection with the open sea and within which sea water is measurably diluted with fresh water derived from land drainage. The term has traditionally been applied to the lower reaches of rivers into which sea water intrudes and mixes with fresh water as well as to bays, inlets, gulfs and sounds into which several rivers might empty and in which the mixing of fresh and salt water occurs.

Distinctions between estuaries are usually made based on the prevailing physical oceanographic conditions (principally the salinity distribution) which are governed by the geometry of the estuary, the magnitude of fresh water flow into the estuary, and the magnitude and extent of the tidal motion. The four principal categories into which estuaries are divided using these criteria are well mixed, stratified, arrested salt wedge and fjord entrainment estuaries, although a single estuary can vary seasonally from one type to another. See Officer (1976).

 

etesian

A Greek term for winds that blow at times in summer (May to September) from a direction ranging from northeast to northwest in the eastern Mediterranean. In Turkey these winds are known as ``meltemi''.

 

ETOPO5

A five-minute resolution database of land elevations and ocean depths. The National Geophysical Data Center (NGDC) has an interactive online ETOPO5 database with which portions of the database can be selected and downloaded.

 

ETP

Abbreviaton for eastern tropical Pacific.

 

EU

Abbreviation for Eurasian Oscillation.

 

eukaryotic

Descriptive of organisms with cells having a distinct nucleus. This includes all protists, fungi, plants and animals.

 

Euler equations

More later.

 

Eulerian mean circulation

In oceanography, the time-averaged flow field in a fixed coordinate system. This can be remarkably different from the synoptic mean circulation. See Schmitz and McCartney (1993).

 

Eulerian velocity

That velocity which would be measured by a current meter at a fixed point. Compare and contrast to Lagrangian velocity and .

 

EUMETSAT

Abbreviation for European Meteorological Satellite Organization, an intergovernmental agency which provides operational meteorological data for its member states.

 

euphotic zone

In the ocean, the sunlit layer consisting of the upper 100 m or so in which most of the primary productivity takes place. The depth varies geographically and seasonally and can range from a few meters in turbid waters near the shore to 120 m in the Sargasso Sea. It is a zone with sharp gradients in illumination, temperature and salinity, and is the upper of three vertical zones that comprise the pelagic part of the ocean, the other two being the middle mesopelagic and the lower bathypelagic zones. It is also known as the photic zone.

 

Eurafrican Mediterranean Water

In physical oceanography, a water mass that leaves the Strait of Gibraltar with a temperature of about 13.5 deg. C and a salinity of 37.8 but is transformed by mixing to a temperature and salinity of 11-12 deg. C and 36.0-36.2 within 250 km. From there it spreads isopycnally across the ocean, mixing gradually with the water above and below.

 

eustatic

Descriptive of global sea level variations due to absolute changes in the quantity of seawater, the most recent significant examples of which have been caused by the waxing and waning of continental ice sheets during glaciation cycles.

 

eutrophic

A situation in which the increased availability of nutrients such as nitrate and phosphate (e.g. from the use of agricultural fertilizers and the combustion of fossil fuels) stimulates the growth of plants such that the oxygen content is depleted and carbon sequestered. It is hypothesized that this might serve as a negative feedback to an increase in atmospheric CO2.

 

evaporative cooling

A phenomenon wherein the evaporation of water from saturated air (when, for example, it mixes with drier air) cools the air due to the absorption of latent heat.

 

evaporite

A water-soluble mineral (such as halite, gypsum, or anhydrite), or a rock composed of such minerals, precipitated out of saline water bodies such as salt lakes.

 

evapotranspiration

Evaporation plus the water discharged into the atmosphere by plant transpiration, i.e. the removal of water from the surface to the air with an accompanying change in phase from the liquid to the vapor form.

 

evolutionary biology

More later.

 

exitance

The irradiance from below a unit area, below being relative to the direction of the original radiation source.

 

Exner function

The Exner function is given by

where p is the atmospheric pressure, a reference pressure, and the ratio of the specific heats of a perfect gas. It is used in studies of compressible adiabatic flow.

 

exosphere

The outermost layer of the atmosphere. It has no clear outer boundary but merges imperceptibly with interstellar space, and its lower boundary is almost as indistinct at an altitude of about 370 miles between the exosphere and the ionosphere. It is mainly composed of hydrogen and helium, with a small quantity of molecular oxygen up to around 370 miles. Helium gradually vanishes with increasing altitude to about 1,500 miles, after which the exosphere is almost entirely comprised of hydrogen.

 

explicit scheme

In numerical modeling, an integration algorithm that temporally advances an approximate solution via discrete steps using only information from previous time steps. These are computationally simpler than implicit schemes but require shorter time stepping intervals. See Kowalik and Murty (1993).

 

export flux

See biological pump.

 

export production

In biological oceanography, the loss rate of organic carbon (and nitrogen) from the surface ocean layer to the ocean interior.

 

EXPRESSO

Acronym for the Experiment for Regional Sources and Sinks of Oxidants, a component of GTCP implemented to quantify fluxes of numerous chemical species over a range of spatial scales from the individual leaf, branch, and soil surface up to landscape and regional scales. See the EXPRESSO Web site.

 

extensive parameter

A determining parameter of a system that is proportional to the size and mass of the system, e.g. volume, internal energy, enthalpy and entropy, as opposed to an intensive parameter.

 

extinction event

A general name given to any of the several mass extinctions of taxa found in the data record of Earth history.

 

extreme events

In the context of climate change, extreme events are infrequent meteorological events that surpass a certain threshold. Observations indicate no compelling evidence that extreme weather events or climate variability has increased globally in the 20th century, although the available data is poor and intermittent in many cases and therefore the analyses aren't comprehensive. There is some evidence for regional changes in extremes and climate variability, although some points to greater and some to lower variability. There is no clear picture from the data as yet.

The present generation of GCMs lack the resolution needed to accurately model these synoptic and short time scale events, and the integrations are also usually too short in duration to permit statistical analysis of local weather extremes. However, using other lines of evidence such as physical reasoning, inferring extreme events from larger patterns like mid-latitude storm tracks, and results from the occasional high resolution model experiment, some tentative assessments can be made. Small changes in either the mean climate or its variability may produce relatively large changes in the frequency of extreme events, with a change in the variability having a stronger effect than a comparable change in the mean. A general warming trend can tend to increase extreme high temperatures as well as decrease the number of winter days with extreme low temperatures. Daily temperature variability may decrease with increased CO2 in some regions, with increased precipitation variability over a few areas. Lastly, some results suggest that a warmer climate will lead to an increase in precipitation intensity and therefore more extreme events, with more frequent and severe drought periods seen in some cases. See Houghton and Filho (1995).