Ea-Em

 

EAC

Abbreviation for East Australian Current.

 

Early Medieval Warm epoch

See Little Climatic Optimum.

 

EARSeL

Acronym for the European Association of Remote Sensing Laboratories. See the EARSeL Web site.

 

earth tide

To be completed.

 

EASOE

Acronym for the European Arctic Stratospheric Ozone Experiment, the aim of which was to take measurements of key chemical species that would provide information to explain the observed northern hemisphere ozone loss. See the EASOE Web site.

 

East Arabian Sea Water

See Bay of Bengal Water.

 

East Auckland Current

The continuation of the East Australian Current east of New Zealand. It forms and is part of an anticyclonic eddy near 37 deg. S off of East Cape. This eddy is found in the same location throughout the years and as such is thought to be topographically controlled. The further extension of this current has a bimodal nature that changes seasonally. During the summer most of its transport continues along the New Zealand coast all the way to Chatham Rise as the East Cape Current. In the winter part of it separates from the shelf and continues as a zonal flow into the open ocean, forming a temperature front near 29 deg. S that is distinguishable from another shallow front near 25 deg. S called the Tropical Front, the northern limit of eastward flow in the subtropical gyre. See Tomczak and Godfrey (1994).

 

East Australian Current

The western boundary current of the southern hemisphere in the Pacific Ocean. It is the weakest of the world's boundary currents, carrying about 15 Sv in the annual mean near 30 deg. N, yet is also associated with strong current instabilities. The relative weakness is due mostly to the flow through the Australasian Mediterranean Sea and the instabilities probably result from the current following the coast and then suddenly separating somewhere near 34 deg. S to follow the east coast of New Zealand (where it is known as the East Auckland Current). It is stronger and reaches further inshore during the summer, with flow speeds reaching 1 m/s during the summer, and the maximum transport has been estimated at around 30 Sv (although the intermittent nature of the current makes such estimates somewhat suspect).

The path it follows from Australia to New Zealand is called the Tasman Front, which separates the warmer waters of the Coral Sea from the colder waters of the Tasman Sea. This front develops meanders which travel westward, impinge upon the Australian coast, and ultimately separate from the current and form eddies. About 3 eddies are spawned per year (with 4-8 existing at any one time in recognizable form) with most being anticyclonic or warm core eddies since the meander closest to the coast always extends to the south. The meandering and eddy-shedding behavior of the current combined with its weak flow sometimes make it difficult to even distinguish it as a current, and the location of the Tasman Front can be meaningfully defined only in statistical terms. See Tomczak and Godfrey (1994).

 

East China Sea

More later.

 

East Greenland Current

More later.

 

East Indian Current

A seasonal and northward flowing current found in the western part of the Bay of Bengal from about January until October. The weak and variable currents found early in the year strengthen with the Northeast Monsoon, exceeding 0.5 m/s by March and ranging from 0.7-1.0 m/s through May and June. This current flows counter to the wind, apparently as an extension of the North Equatorial Current, although a convincing dynamical explanation has yet to be offered. The northward flow gradually weakens with the advent of the Southwest Monsoon, with the currents to the north and close to the shelf beginning to reverse in September. By late October, the East Indian Current has completely reversed into the East Indian Winter Jet. See Tomczak and Godfrey (1994).

 

East Indian Winter Jet

A seasonal southwestward flowing western boundary current found in the western Bay of Bengal from late October through around late December. It features velocities consistently above 1 m/s as it flows southwestward, eventually turning west and following topographic contours as it passes Sri Lanka and feeds all its waters into the Arabian Sea. In late December its northern part fades, eventually to become the East Indian Current, and the southern part merges with the developing North Equatorial Current.

 

East Korea Current

See Tsushima Current.

 

East Siberian Sea

One of the seas found on the Siberian shelf in the Arctic Mediterranean Sea. It is located between the Laptev Sea to the west and the Chuckchi Sea to the east, and adjoins the Arctic Ocean proper to the north.

 

Eastern North Pacific Central Water

In physical oceanography, a water mass formed in the region of the surface salinity maximum just south of 30 deg. N where salinities greater than 35 are found year round. This is reflected in the portion of ENPCW above 17 deg. C, which has salinities higher than those of all other water masses in the vicinity. It is fresher than both WNPCW and NPEW at temperatures below 17 deg. C, and saltier in the upper thermocline waters warmer than this. It is bounded to the west from WNPCW at about 170 deg. E, and to the south from NPEW at about 12-14 deg. N. See Tomczak and Godfrey (1994), p. 165.

 

Eastern South Pacific Central Water

In physical oceanography, a water mass formed between 150-180 deg. W (by processes not yet well understood) and separated from the WSPCW by a gradual transition zone from 145-100 deg. W., from which it is distinguished as being fresher at all T-S values. It is bound to the north by SPEW, from which it is also distinguished by being fresher at all T-S points, to the south by the STC, and to the east by a not yet well understood area having salinities as low as 34.1 east of 90 deg. W. See Tomczak and Godfrey (1994), p. 164.

 

EAW

Abbreviation for East Arabian Sea Water.

 

EAZO

Abbreviation for Energetically Active Zones of the Ocean.

 

EBBR

Abbreviation for Energy Balance Bowen Ratio, a measurement system used in the ARM program. It is a ground-based system using in situ sensors to estimate the vertical fluxes of sensible and latent heat at the local surface. The flux estimates are made from measurements of net radiation, soil heat flow, and the vertical gradients of temperature and relative humidity via the Bowen ratio energy balance technique. See the EBBR Web site.

 

EBC

Abbreviation for Eastern Boundary Current.

 

EBM

See energy balance model.

 

eccentricity

This describes the variations in the ellipticity of the earth's orbit around the sun, which varies between near circularity and an ellipticity of about 0.06 at a main period of 413,000 years. The eccentricity is one of three chief components of the Milankovitch theory, the other two being obliquity and precession.

 

ECCN

Abbreviation for the European Climate Computer Network, a proposal to link the four dedicated climate computer centers in Europe, i.e. the Hadley Center in Bracknell, Meteo-France in Toulouse, the IPSL in Paris, and the DKRZ in Hamburg, to a common facility offering access to supercomputer resources as well as a hierarchy of climate models, diagnostic software and analysis procedures to all climate researchers in Europe. For more details see the ECCN Web site.

 

ECHAM

Abbreviation for European Center for Medium Range Weather Forecasts modified in HAMburg model, an atmospheric circulation model series developed and used at the DKRZ. They are low-resolution versions of the numerical weather forecasting model developed at ECMWF, modified for climate applications. The modifications include introducing cloud water as a prognostic variable, the inclusion of a diurnal cycle, parameterization of sub-grid scale processes such as radiation, cloud formation, precipitation, convection and turbulent mixing, and the inclusion of runoff into the ocean via a simple surface hydrology model.

 

ECHO

Acronym for a global coupled ocean-atmosphere circulation model developed and used at the DKRZ. It consists of a version of ECHAM coupled with a version of HOPE.

 

echo ranging

More later.

 

echo sounder

More later.

 

ECLIPS

Acronym for the Experimental Cloud Lidar Pilot Study. See Platt and co authors (1994).

 

eclipse year

The interval of time between two successive passages of the Sun through the same node of the Moon's orbit. It is equal to 346.62003 days.

 

ecliptic

The great circle in which the plane containing the centers of the Earth and the Sun cuts the celestial sphere.

 

ECMWF

Abbreviation for European Centre for Medium-Range Weather Forecasts, an international organization whose objectives are to develop numerical methods for medium-range weather forecasting, prepare medium-range weather forecasts for distributions to the meteorological services of the member states on a regular basis, perform research directed towards improving forecasts, and collecting and storing appropriate meteorological data. See the ECMWF Web site.

 

ecogeographical rule

A rule that summarizes observations about how warm-blooded species vary in a regular way with climate.

 

ecological efficiency

In marine ecology, the amount of energy extracted from a given trophic level divided by that supplied to the same trophic level. This is the product of two other coefficients, the ecotrophic efficiency and the growth efficiency. See Barnes and Hughes (1988).

 

ecological race

See ecotype.

 

ecology

More later.

 

ecosystem

All the individuals, species and populations in a spatially defined area, the interactions among them, and those between the organisms and the abiotic environment. See Heywood (1995).

 

ecotrophic efficiency

In marine ecology, the proportion of the annual production of a trophic level taken by consumers. This is one of two factors comprising the ecological efficiency. See Barnes and Hughes (1988).

 

ecotype

A genetically distinct local population of a species made up of individuals with similar environmental tolerances and that are specialized to meet local environmental conditions. These populations show minor changes in morphology and/or physiology but are still able to interbreed, although they have to potential to develop in a new species. This is also called an ecological race. See Collinson (1988).

 

ECSN

Abbreviation for the European Climate Support Network. See the ECSN Web site.

 

ECT

Abbreviation for equatorial cold tongue, a tongue of relatively cold water between the NWT and the SWT at the eastern boundary of the WPWP. It is located on the equator and disappears during an El Nino event. See Ho et al. (1995).

 

ectotrine

A biologically active substance whose presence in minute quantities can control marine productivity. Laboratory experiments have demonstrated that many substances excreted by lower forms of marine life can either promote or inhibit growth, although there is no direct evidence that they are important under natural conditions. The most extensively investigated growth promoting compounds are vitamin B12, B1 (thiamine) and biotin. See Riley and Chester (1971).

 

EDC

Abbreviation for EROS Data Center, a data management, systems development, and research field center of the USGS's National Mapping Division. It was established in the early 70s to receive, process and distribute data from NASA Landsat satellites and holds the world's largest collection of space and aircraft acquired imagery of the Earth. EDC also develops and oeprates advanced systems for receiving, processing, distributing, and applying land related Earth science, mapping, and other other geographic data and information. See the EDC Web site.

 

eddy heat flux

In physical oceanography, the total meridional heat transport due to mesoscale eddies. This has also been used to refer to the correlation of time-dependent fluctuations of velocity and temperature across a section, which is not indicative of the total heat transport due to eddies. Eddies can also induce a thermally driven, overturning cell in subtropical gyres that is analogous to the Ferrel cell in the atmosphere. This cell contributes to the time-averaged transport and its contribution may be as large as that of the time-dependent correlations. See Cox (1985).

 

eddy-induced transport velocity

An additional velocity which must be added to the large-scale velocity to properly advect large-scale tracers in numerical circulation models. This is due to the effective transport velocity not being equivalent to the Langrangian-mean velocity when the diffusivity is not spatially homogeneous. See Gent et al. (1995).

 

eddy viscosity

A coefficient used to achieve closure in the Reynolds equations for turbulent flow. The assumption is made that the Reynolds stresses are related to the velocity gradients of the flow by a viscosity analogous to the molecular viscosity, i.e. a turbulent or eddy viscosity. The utility of the analogy is strained by the fact that while the molecular viscosity is a property of the fluid, the eddy viscosity is a property of the flow. As such the specification of the eddy viscosity has more than a little of the air of the ad hoc about it since it is usually found via a trial-and-error procedure wherein it is varied until a numerically simulated flow reasonably replicates a known flow. The value thus obtained diagnostically is then used for prognostic simulations, a procedure that is questionable due to the abovementioned fact of the eddy viscosity being a property of the flow rather than the fluid. That is, if the flow is remarkably different, then the eddy viscosity may also be remarkably different.

In the ocean eddy viscosity values range typically from 10 to 10**5 m2/s in the horizontal and from 10**-5 to 10**-1 m2/s in the vertical, with both values more often found towards the higher ends of their ranges.

 

edge wave

To be completed.

 

EDQNM

Abbreviation for Eddy Damped Quasi-Normal Markovian, a subfilter closure model applied in spectral wavenumber space rather than physical space which considers interactions between resolved and subfilter wavenumbers by considering the statistics of their possible interactions. The EDQNM achieves closure by modeling the 4th spectral moments. The is one of several closure techniques used when applying large eddy simulation model. See Mason (1994).

 

EEP

Abbreviation for eastern equatorial Pacific.

 

EESC

Abbreviation for Earth and Environmental Sciences Center, a division of PNL whose mission is to solve society's environmental and earth resources problems through interdisciplinary work founded on developing research capabilities maintained as a national resource by the DOE. See the EESC Web site.

 

effective scattering cross-section

The ratio of backward scattering intensity to density of irradiation flux. See Kagan (1995).

 

effective rainfall

The proportion of precipitation that is not evaporated and is therefore available for various uses. It is defined as precipitation less evaporation and normally computed monthly or annually.

 

effective transport velocity

The sum of the large-scale velocity and the eddy-induced transport velocity. This is velocity at which tracers are advected in large-scale circulation models. See Gent et al. (1995).

 

e-folding time

The time it takes a system to reduce an imposed displacement to a factor of 1/e of the displaced value. This is a common way of expressing the equilibration time of a system. The e-folding concept is often applied to distances as well as times.

 

EGCM

Abbreviation for Eddy-resolving General Circulation Model.

 

EHF

Abbreviation for extremely high frequency, an electromagnetic spectrum waveband ranging from 30 to 300 GHz.

 

EIL

Abbreviation for entrainment interfacial layer.

 

einstein

A unit equal to 6.022 x quanta, or one mole of photons.

 

EKE

Abbreviation for eddy kinetic energy.

 

Ekman current meter

A mechanical current meter that comprises a propeller with a mechanism to record the number of revolutions, a compass and a recorder with which to record the direction, and a vane that orients the instrument so the propellor faces the current. It is mounted on a free-swinging vertical axis suspended from a wire and has a weight attached below. The balanced propellor, with from four to eight blades, rotates inside a protective ring. The position of a lever controls the propeller. In down position the propellor is stopped and the instrument is lowered, after which reaching the desired depth a weight called a messenger is dropped to move the lever into the middle position which allows the propeller to turn freely. When the measurement has been taken another weight is dropped to push the level to its highest position at which the propeller is again stopped.

The propeller revolutions are counted via a simple mechanism that gears down the revolutions and counts them on an indicator dial. The direction is indicated by a device connected to the directional vane that drops a small metal ball about every 100 revolutions. The ball falls into one of thirty-six compartments in the bottom of the compass box that indicate direction in increments of 10 deg. If the direction changes while the measurement is being performed the balls will drop into separate compartments and a weighted mean is taken to determine the average current direction.

This is a simple and reliable instrument whose main disadvantage is that is must be hauled up to be read and reset after each measurement. Ekman solved this problem by designed a repeating current meter which could take up to forty-seven measurements before needing to be hauled up and reset. This device used a more complicated system of dropping small numbered metal balls at regular intervals to record the separate measurements. See Sverdrup et al. (1942).

 

Ekman repeating current meter

See Ekman current meter.

 

Ekman dynamics

In oceanography, the process of surface wind stress driving a relatively shallow upper ocean flow that transports water to the left/right and the southern/northern hemisphere.

 

Ekman layer

To be completed.

 

Ekman number

In oceanography, a dimensionless number expressing the ratio of frictional (or viscous) to Coriolis forces. It can be expressed as

where is the kinematic viscosity, D a vertical length scale, and f the Coriolis parameter. A small Ekman number can be interpreted as the condition that frictional forces are sufficiently weak such that the natural decay time due to viscous dissipation in the Ekman layer is large compared to a rotation period, i.e. that the spin-down is dominated by rotational rather than frictional processes. See Kraus and Businger (1994) (p. 31) and () (p. 180).

 

Ekman pumping

In oceanography, a process that is the result of a combination of Ekman dynamics and horizontal variations in the wind stress. The resulting convergence and divergence of the surface flow will force vertical water motion called Ekman pumping or suction, respectively.

 

El Nino/Southern Oscillation

El Nino refers to a massive warming off the coastal waters of Peru and Ecuador and the Southern Oscillation to the related atmospheric component of this phenomenon, often abbreviated as ENSO. The ocean warming covers a band from 10 deg. N to 10 deg. S and extends more than 90 deg. of longitude. Typically, the warming starts late in the boreal spring or summer and builds to a peak at the end of the year, with the event usually over by the following summer. It is a quasi-periodic phenomenon with global consequences in the form of flooding, droughts, and other phenomena. See Cane (1986), Enfield (1989), Neelin et al. (1994), Philander (1990), and Philander and Rasmusson (1985).

 

ELDORA

The Electra Doppler Radar is an airborne Doppler weather radar instrument designed to provide high-resolution measurements of the air motion and rainfall characteristics of very large storms that are frequently too large or too remote to be adequately observed by ground-based radars. It is commonly known as ELDORA in the United States and as ASTRAIA (Analyese Stereoscopic par Impulsions Aeroporte) in France, and more fully known as ELDORA/ASTRAIA. See Hildebrand et al. (1996).

 

elevation angle

See local elevation angle.

 

Elster

The Scandinavian name given to the Kansan glacial period.

 

EMAC

Acronym for the European Multi-Sensor Airborne Campaign. See the EMAC Web site.

 

emagram

In meteorology, a diagram of the temperature (T) versus the natural log of the pressure (ln p). The energy available for vertical convection is calculated by measuring the areas between the prevailing lapse rate and the adiabatics followed by and ascending parcel on an emagram. See Byers (1944).

 

EMEX

Acronym for Equatorial Mesoscale EXperiment, an experiment conducted over the tropical oceanic area north of Australia in Jan.-Feb. 1987. It explored the vertical air motions and other kinematic properties of tropical mesocale convective-cloud systems by direct aircraft penetration. The objectives of EMEX were to document, as intensively and directly as possible, the vertical profile of vertical velocity and other kinematic structures over the ocean near the equator with the most up-to-date instrumentation available and to investigate the physical mechanisms responsible for the convective and stratiform components of the observed cloud systems. See Webster and Houze Jr. (1991).

 

emissivity

The ratio of the emittance from a body to that of a black body emitter at the same temperature, i.e. the degree to which a real body approaches a black body radiator.

 

emittance

The rate at which radiation is emitted from a unit area.

 

empirical orthogonal function

EOF analysis provides a convenient method for studying the spatial and temporal variability of long time series of data over large areas. It splits the temporal variance of the data into orthogonal spatial patterns called empirical eigenvectors. A set of orthogonal spatial modes can be identified such that, when ordered, each successive eigenvector explains the maximum amount possible of the remaining variance in the data, and each eigenvector pattern is associated with a series of time coefficients that describe the time evolution of the particular spatial mode. The modes are orthogonal, which means that any two modes are uncorrelated in space and time and, as such, no one mode is related to any other. See Peixoto and Oort (1992) and Preisendorfer (1988).

 

EMW

See Eurafrican Mediterranean Water.