Ea-Em

EAC

Abbreviation for East Australian Current.

EAC

Abbreviation for East Arabian Current.

EAE

Abbreviation for Eastern Atlantic Experiment.

EASAP

Abbreviation for East Asian Seas Action Program.

East Africa Coast Current

See Somali Current.

East Arabian Current

A strong northeastward flowing current along the Saudi Arabian coast. It is part of the monsoonal circulation in the area and as such exists from about April through October, being fully established by mid-May with velocities ranging form 0.5-0.8 m/s. It is also part of a strong coastal upwelling system during those months when it flows strongest.

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$^\circ$ 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$^\circ$ S that is distinguishable from another shallow front near 25$^\circ$ 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$^\circ$ 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$^\circ$ 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.

The pronounced seasonal cycle is described by Ridgway and Godfrey (1997):

Maps of the annual-frequency component of the surface and depth-integrated steric heights ( h and P) show the development and progression of the EAC flow regime through a complete seasonal cycle. The EAC has a strong seasonal cycle from 25°S to 45°S, with strongest southward flow in austral summer. The seasonal cycle in surface flow over the continental shelf is documented by two independent methods, geostrophically, using cross shelf sea level gradients derived from coastal tide gauge data and steric heights at the continental shelf edge, and directly from merchant ship observations. The two estimates are in good agreement. The seasonal cycle in the EAC is more pronounced than in other mid-latitude western boundary currents for which data are available. At 28°S, the strength of the total Tasman Sea transport (southward flow) varies between a minimum transport of 7 Sv in winter (July) to a maximum of 16 Sv in summer. The semiannual frequency components of h and P is important near 30°S near the EAC outflow, but not elsewhere. The seasonal cycle of the EAC is not due to strong seasonal variations in Tasman Sea wind stress curl east of the region of interest. Seasonally reversing zonal flows occur offshore north of 25°S, which are apparently locally forced by reversing wind stress curls; but if these flows were fed from the south by the EAC current system, the EAC would have to be weaker in summer, not stronger. The Leeuwin Current Extension along Australia's west and south coasts may pass up the east coast of Australia, providing an important contribution to the enhanced southward flow of the EAC in summer. The vigorous anticyclonic eddies of the EAC also show a marked seasonal cycle and this is probably an important part of the mechanism for the strong seasonal cycle of the EAC south of 25°S. The location of the strongest anticyclonic eddy in the EAC moves steadily southward throughout the summer season, and the phase of the coastal EAC appears also to move southward contrary to the expectations of linear theory, and to the hypothesis that the Leeuwin Current Extension is the major cause of the seasonal cycle.

See Ridgway and Godfrey (1997) and Tomczak and Godfrey (1994).

East Cape Current

See East Auckland Current.

East China Sea

See Tomczak and Godfrey (1994), Guan (1994), Hu (1994), Jilan (1998) and Katoh et al. (2000).

East Coast Ocean Forecast System (ECOFS)

A cooperative program among NOS, NCEP, GFDL, and AOS to develop a system capable of producing useful nowcast and forecast information for the east coastal region of the United States. See the ECOFS Web site.

East Greenland Current

More later. See Foldvik et al. (1988) and Woodgate et al. (1999).

East Greenland Ice Stream

See Wadhams (1986).

East Greenland Polar Front

See Johannessen (1986).

East Icelandic Current

See Swift (1986).

East Icelandic Water

A water mass found in the area of the Iceland-Faroe Ridge. See Hansen and Osterhus (2000).

East India Coastal Current

See Shankar et al. (1996).

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 Sea

A semi-enclosed, marginal sea surrounded by Korea, Japan and Russia. See Preller and Hogan (1998).

[http://key.kordi.re.kr/home/pores.htm]

East Siberian Sea

One of the seas found on the Siberian shelf in the Arctic Mediterranean Sea. The western boundary passes from the meridian at the northern tip of Kotelny Island along the continental shoal margin (79$^\circ$ N, 139$^\circ$ E) to the northern end (Anisiy Cape), then along the western shore floolwing the eastern boundary of the Laptev Sea. The northern boundary passes by the edge of the continental shoal from 76$^\circ$ N, 180$^\circ$ E, then along the eastern boundary along meridion 180$^\circ$ up to Wrangel Island, then along the northwestern shore to Blossom Cape, and then down to Yaken Cape on the mainland. The southern boundary passes along the mainland coast from Yakan Cape to Svyatoy Nos Cape. It adjoins the Laptev Sea to the west, the Chuckchi Sea to the east and the Arctic Ocean proper to the north. The largest span is about 640 nautical miles, and the largest width about 506 nautical miles. The bathymetry is very level and comparatively shallow compared with the other marginal seas of the Arctic Basin. The prevailing depths of the western and central regions are 10-20 m, and 30-40 m in the eastern region.

The first scientific data from this sea was collected on the 1922-1924 expedition of the Maud and published by Sverdrup (1929). This remained the only accessible data until the military vessels USS Barton and USCGS Northwind surveyed the area in 1962 and 1966. The first U.S. research vessel to enter the East Siberian Sea was the RV Alpha Helix in 1995. It deployed surface drifters in the ice-free summer shelf waters and conducted hydrographic surveys to investigate the influence of the Kolyma River on the shelf circulation.

The freshwater input of the Kolyma River is of prime hydrographic significance to the East Siberian Shelf Sea. The annual discharges vary from below 2000 ${m^3}{s^{-1}}$ to nearly 5000 ${m^3}{s^{-1}}$, with the 1936-1996 mean about 3160 ${m^3}{s^{-1}}$. The discharge is highly seasonal with more than 90% occurring between June and September, increasing from a May average of less than 1000 ${m^3}{s^{-1}}$ to a June average of more than 10,000 ${m^3}{s^{-1}}$ (with the average monthly discharge during the winter from November through April less than 500 ${m^3}{s^{-1}}$). The Lena River to the west also contributes fresh water, with a peak discharge that can exceed 100,000 ${m^3}{s^{-1}}$ in June.

The waters of the East Siberian Sea are fresh and cold, with surface temperatures varying between 0$^\circ$ and 2$^\circ$C and bottom temperatures near the freezing point. Large horizontal salinity (although not temperature) gradients are found at depth. The shelf waters are generally colder, saltier, and thus denser than the offshore waters. The salinities range from almost 0 near the Kolyma River mouth to a maximum of 33. The three most significant water masses are resident shelf waters, freshwater from river discharges, and freshwater from seasonal ice melt.

The buoyancy forcing due to the freshwater input would be expected to result in an eastward bound buoyancy-driven flow coastal current, but the drifters in a 1995 survey (Münchow et al. (1999)) indicated a 50-day mean westward flow reaching 0.1 $m{s^{-1}}$. The river waters were found to be predominant only in the immediate vicinity of the Kolyma Delta. The observed circulation was postulated to be due to some as yet unknown combination of:

• a line source of buoyancy caused by the melt water left by an ice edge that retreated 100 km in less than two weeks;
• large-scale barotropic and/or baroclinic pressure gradients imposed from the Laptev Sea in the west through Laptev Strait; and
• decadal-scale scale climate oscillations (i.e. atmospheric pressure anomalies) that induce alternating cyclonic and anticyclonic circulation regimes.

See Sverdrup (1929), Pavlov (1998), Münchow et al. (1999) and Münchow et al. (1999).

East Spitsbergen Current

See Pfirman et al. (1994).

East Wind Drift

The westward flowing current close to the Antarctic continent driven by the polar easterlies.

Eastern Atlantic Experiment (EAE)

A 1996-1997 experiment that was one of the three main components forming the MAGE component of ACSOE. EAE was an extensive study of the speciation of sulphur and nitrogen in both clean and moderately polluted atmospheres, and involved the measurement of DMS and other gases in the ocean and the calculation of fluxes into the atmosphere, combined with the measurement of the speciation of sulphur and nitrogen in both gas and size-fractionated aerosol phases. The objectives were:

• to quantify the input of DMS into a parcel of air;
• to examine the oxidation of DMS and its reaction with nitrogen species with time;
• to investigate the formation of new particles that result from these transformations; and
• to discriminate between natural and anthropogenic fractions of sulphur and nitrogen using isotopic measurements.

[http://www.uea.ac.uk/~acsoe/easta.htm]

eastern boundary current

See Wooster and Reid (1963).

Eastern Equatorial Pacific (EEP)

See Wyrtki (1966).

Eastern Mediterranean Deep Water (EMDW)

A water mass found in the Mediterranean Sea. EMDW extends from the overlying Levantine Intermediate Water (LIW) to the bottom, although the layer of EMDW between 700 m and 1600 m is considered transitional since it is modified by LIW. This layer has been called Transitional Mediterranean Water (TMW). The Adriatic Sea is considered the source of cold and less saline EMDW, which is formed in the winter in the Ionian Sea by the mixing of deep and cold Adriatic water (that enters the Ionian via Otranto Strait) with transformed LIW and, to a lesser extent, by mixing with deep Cretan waters. The core values of the EMDW are remarkably invariant through the basin with $\theta <$ 13.4$^\circ$ C, T = 13.6$^\circ$ C, S = 38.7, and $\sigma_\theta \ge$ 29.17 kg m$^{-3}$. See POEM Group (1992), Roether et al. (1996), Malanotte-Rizzoli et al. (1997), Stergiou et al. (1997) and Theocharis et al. (1999).

Eastern North Atlantic Water (ENAW)

A water mass defined by Harvey (1982) and () to describe water found west of Ireland and Iberia. The ENAW definition can be subsumed into the broader definition of North Atlantic Subpolar Mode Water, and thus can be seen as a variety of the latter. See Read (2001).

Eastern North Atlantic Central Water (ENACW)

See Poole and Tomczak (1999).

Eastern North Pacific Central Water (ENPCW)

In physical oceanography, a water mass formed in the region of the surface salinity maximum just south of 30$^\circ$ N where salinities greater than 35 are found year round. This is reflected in the portion of ENPCW above 17$^\circ$ 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$^\circ$ C, and saltier in the upper thermocline waters warmer than this. It is bounded to the west from WNPCW at about 170$^\circ$ E, and to the south from NPEW at about 12-14$^\circ$ N. See Tomczak and Godfrey (1994), p. 165.

Eastern South Atlantic Central Water (ESACW)

See Poole and Tomczak (1999).

Eastern South Pacific Central Water

In physical oceanography, a water mass formed between 150-180$^\circ$ W (by processes not yet well understood) and separated from the WSPCW by a gradual transition zone from 145-100$^\circ$ 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$^\circ$ W. See Tomczak and Godfrey (1994), p. 164.

EASTROPAC

Acronym for Eastern Tropical Pacific, a research project.

EASW

Abbreviation for East Arabian Sea Water.

EATSS

Acronym for European Atlantic Time and Space Series study, a proposed program for establishing coordination of European research activities along the historically studied 20$^\circ$W meridian from 20 to 60$^\circ$N. EATTS will be sponsored under the auspices of SOMARE.

[http://www.pml.ac.uk/amt/somare/workshop%201/WS1-Report.htm]

EAZO

Abbreviation for Energetically Active Zones of the Ocean.

ebb current

The tidal current existing during any time the height of the tide is decreasing. These generally flow in a seaward direction. This has been erroneously called ebb tide.

ebb interval

The interval between the transit of the moon over a meridian and the time of strength of ebb of the following tide.

ebb strength

See strength of ebb.

ebb tide

See falling tide.

EBC

Abbreviation for eastern boundary current.

ECCO

Acronym for Estimating the Circulation and Climate of the Ocean, a consortium consisting of MIT, JPL and SIO formed under the NOPP and funded by NSF, NASA and ONR. The consortium intends to bring ocean state estimation from its current experimental status to that of a practical and quasi-operational tool for studying large-scale ocean dynamics, designing observational strategies, and examining the ocean's role in climate variability. The central goal is the production and evaluatino of continuing 3-D estimates of the global state of the ocean, and the main task is to bring together a global GCM with existing global data streams to obtain the best possible estimate of the time-evolving ocean circulation and related uncertainties.

[http://www.ecco.ucsd.edu/]

echograph

A recording echo sounder.

echo sounder

An instrument used to determine ocean depth by measuring the time needed for a sound wave to travel from the ship to the ocean floor and return. The first reliable acoustical sounding machine was built by A. Behm in 1919, who called it an echo sounder. An echo sounder consists of three main components: the sound transmitter, the sound receiver, and a device to measure time. See Dietrich (1963).

Eckart, Carl (1902-1973)

See Munk and Preisendorfer (1988).

[http://scilib.ucsd.edu/sio/archives/siohstry/eckart-biog.html]

ECLAT

Acronym for Etudes Climatiques dans l'Atlantique Tropical, a multidisciplinary program designed to become the French contribution of CLIVAR in the tropical Atlantic. The PIRATA program will be part of ECLAT. See the ECLAT Web site.

ECOANTAR

A research cruise carried out on the R/V Hesperides from Jan. 2 to Feb. 1, 1994 in the eastern basin of the Bransfield Strait. A total of 130 hydrographic stations were occupied, and 180 surface to bottom profiles collected. See López et al. (1999).

ECOMARGE

A program to study shelf edge exchange processes in the Gulf of Lions. See Monaco et al. (1990).

eddy correlation technique

A method for estimating the ocean surface wind stress wherein the directional components of the near-surface turbulent stress covariance in the atmospheric boundary layer are measured. The vertical stress is defined as:

$$\tau (z)\,=\,-\rho\,\overline{\mathbf{u}w}$$

where $\mathbf{u}$ is the horizontal vector velocity and $w$ the vertical velocity component. In terms of its scalar components, the magnitude of the wind stress is given by:

$$\tau\,=\,\rho\, {{\left[ {{\left(\overline{uw}\right)}^2}\,+\, {{\left(\overline{vw}\right)}^2} \right]}^{1/2}}$$

and its angle to the mean wind is:

$$\theta\,=\,{\tan^{-1}} \left( {{\overline{vw}} \over {\overline{uw}}} \right)$$

where $u$ and $v$ are the horizontal velocity components. The overbar represents the mean value over a suitable averaging interval. The data must be measured over sufficiently large time and space scales to capture all scales of variability, a task that inevitably presents logistical difficulties.

eddy conduction

See eddy heat flux.

eddy conduction coefficient

See eddy conductivity.

eddy conductivity

The exchange coefficient for the transfer of heat by eddies in turbulent flow, i.e. eddy heat flux. This is also called the eddy conduction coefficient.

eddy diffusivity

eddy heat conduction

See eddy heat flux.

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. This is also called eddy conduction or eddy heat conduction. 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. This is defined in isopycnal coordinates as:

$${\mathbf{u}^*}\,=\, { {\widetilde{{{z'}_\rho}\mathbf{u}'}} \over {\tilde{z}_\rho} }$$

where $\mathbf{u}$ is the horizontal velocity, $z_\rho$ the isopycnal thickness, and the tilde represents an average along an isopycnal surface. This quantity is important since average tracer quantitues are advected by not just the Eulerian mean velocity $\mathbf{\tilde{u}}$ but by the total transport velocity given by:

$$\mathbf{\hat{u}}\,=\,\mathbf{\tilde{u}}\,+\,\mathbf{u^*}$$

This velocity is a turbulence correlation and therefore must be specified by some type of turbulence theory or parameterized. One attempt at the latter defines it as:

$$\mathbf{u^*}\,=\,-{1\over{\tilde{z}_\rho}} {\partial_\rho}(\kappa{\nabla_\rho}\tilde{z}$$

where $\nabla_\rho$ is the horizontal gradient in isopycnal coordinates and $\kappa$ is a scalar diffusivity coefficient. This is also known as the bolus velocity. See Gent et al. (1995) and Dukowicz and Greatbatch (1999).

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

A wave which travels parallel to a coastline with crests normal to the coastline. The height of the wave diminishes rapidly offshore.

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.

effective scattering cross-section

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

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.

EHUX

Acronym for the European Emiliania huxleyi program, a comprehensive experimental and modeling program focused on the calcium carbonate and organic carbon productivity and ocean carbon flux induced by E. huxleyi in the Northeast Atlantic region. It is a component of and complementary to the GEM program. This project aims to characterize the nonlinear nature of the biological involvement in ocean chemistry and the coupling of the fluxes of particulate organic carbon (POC) and particulate inorganic carbon (PIC).

The fundamental objective is the improve understanding of the processes involved in the growth, distribution and role of E. huxleyi in the oceanic carbon cycle. The specific aims include the morphological and genetic characterization of clones from different areas and elucidation of the life cycle; characterization of PIC, POC, biomarker and CO$_2$ productivity as a function of cellular and molecular organization and life cycle stages; parallel mesocosm experiments; quantification of these processes in natural blooms at different stages of development and development of carbon budgets for well defined spring bloom conditions; and the development of descriptive and predictive models. See the EHUX Web site and Harris (1996).

EIC

Abbreviation for Equatorial Intermediate Current.

18$^\circ$ Water

A variety of Subtropical Mode Water (STMW) that forms in the western subtropical gyre of the North Atlantic Ocean, i.e. the area known as the Sargasso Sea. This has also been called Sargasso Sea Water (SSW). See Worthington (1959) and Talley and McCartney (1982b).

EIL

Abbreviation for entrainment interfacial layer.

EIMWT

Abbreviation for Echo Integration-Midwater Trawl.

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$^\circ$. 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. See Price and Sundermeyer (1999).

Ekman number

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

$$Ek\,=\,{\nu\over{{D^2}f}}$$

where $\nu$ 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 Pedlosky (1982) (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.

Eliassen-Palm flux

A concept originally developed as a diagnostic tool for studying the interaction between eddies and the zonal-mean flow in the atmosphere. The Eliassen-Palm flux vector is used to represent eddy momentum and heat transport in such a way that the total eddy-inducing forcing is the divergence of the Eliassen-Palm flux. It can also be used to provide information about wave activity for quasigeostrophic flows, with this application relying on the equality between the divergence of the flux and the eddy potential vorticity flux under the quasigeostrophic approximation. See Lee and Leach (1996).

ELISA

Acronym for Eddies and Leddies Interdisciplinary Study off Algeria, a MAST-3/MATER program and companion to the ALGERS project. ELISA was an interdisciplinary project to investigate the Western Mediterranean Sea, looking at the role of the Algerian Basin through the detailed study of the Algerian Current. The field work took place between July 1997 and July 1998 and involved 44 scientists from 8 countries. The objectives were to study:

• the general circulation of the water masses, i.e. MAW, LIW and WMDW;
• the Algerian eddies origin, structure and trajectories;
• the biological activity associated with the mesoscale dynamic phenomena; and
• the role of the mesoscale dynamics on the biological functioning of the Algerian Basin.

[http://www.com.univ-mrs.fr/LOB/ELISA/]

El Niño

A term originally applied as a description of an annual weak warm current running southward along the coast of Peru and Ecuador during the Christmas holiday, i.e. the Spanish word for ``the boy Christ-child'' is Niño.a The name El Nño eventually became associated with unusually large warmings that occur every few years and effect large changes on the local, regional, and even global climate. It gradually became known that the coastal warming was part of a much larger warming of the upper waters of the Pacific extending as far as the international date line. There is an associated atmospheric phenomenon called the Southern Oscillation, with the combined changes in atmosphere and ocean termed El Niño/Southern Oscillation or ENSO, with El Niño properly referring the warm phase of ENSO. A typical El Niño event begins in the nothern spring or sometimes summer, peaks from November to January in SSTs, and ends the following summer. The opposite phase is similarly called La Niña, i.e. Spanish for ``the girl,'' and features a basinwide cooling in the tropical Pacific. The entire system is called El Niño in many if not most popular accounts.

More quantitative definitions have been proposed for classification purposes. Although none is recognized as official, several objective methods have proved useful. Most involve calculating the deviation from average of temperatures in rectangular regions in the tropical Pacific, with the averaging period, baseline temperatures, qualifying deviation, and specific region varying from definition to definition. The defined averaging regions include: Niño 3 (5$^\circ$N-5$^\circ$S, 90$^\circ$-150$^\circ$W); Niño 3.4 (5$^\circ$N-5$^\circ$S, 120$^\circ$-170$^\circ$W); and Niño 3.5 (5$^\circ$N-10$^\circ$S, 120$^\circ$-180$^\circ$W). A typical calculation would find periods during which 5 month running means of monthly SST anomalies in a given area are +0.4$^\circ$C or more for at least six consecutive months. According to Trenberth (1997), applying this particular procedure to Niño 3.4 picks out most historically prominent El Niño events. See Cane (1986), Enfield (1989), Neelin et al. (1994), Neelin et al. (1998), Philander (1990), Philander and Rasmusson (1985) and Stockdale et al. (1998).

El Niño/Southern Oscillation

See El Niño.

ElbeEstuary

See Kuhl (1972).

electromagnetic fields

See Tyler et al. (1997).

EMDW

Abbreviation for Eastern Mediterranean Deep Water.

EMEX

1. 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). 2. Acronym for Equatorial Monsoon Experiment.

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 normal mode (ENM)

Basis functions that have both the statistical properties of empirical orthogonal functions (EOFs) and the dynamical properties of normal modes, although the orthogonal products used to define orthogonality are related to conserved wave activities such as pseudomomentum or pseudoenergy. These are obtained in a manner similar to EOFs by the diagonalization of a general hermitian problem but with the use of a quadratic form instead of the Euclidean norm, with the quadratic form being a global invariant of the linearized equations about a basic state. ENMs are a diagnostic tool for studying wave behavior and wave interactions, and can also be used as predictors in a long-range forecasting system. They typically beat EOF-based forecasts at long lead times but have slightly poorer scores at short lead times since ENMs are less efficient for data compression than EOFs. See Brunet and Vautard (1996).

empirical orthogonal function (EOF)

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.